Date: Thu, 16 Jun 2011 21:19:26 +0900
Subject: Earthquake (97)
From: Genn Saji
I. I. Recapping on the water purification system
The testing of the third stage, the co-precipitation stage manufactured by AREVA, started later yesterday afternoon for seven hours. The results demonstrated that the DF of 17,000 to 18,000 in cesium. It is amazing, since I thought co-deposition in the salty water is not feasible. The second stage with the US Kurion’s molecular sieve sorption process has already demonstrated the DF of around 3000. Being encouraged by these successful results, the final integrated test is currently underway, starting around 0:00 AM of June 16 to be continued to 17. Currently, one standby pump is being used, since a minuscule leakage was observed in one pump. Since the tests are being performed with low level contaminated water, which is harder to remove radioactive species due to the higher salt ratios, it is anticipated that the integrated DF can be higher in both stages for the highly contaminated water. If successful, the water purification system may start commissioning as early as tomorrow. However, one thing I am still concerned is DF for strontium. The first stage was for oil separation as well as strontium removal. Due to the difficulty of radiological assessment of strontium, the sampling results will become available later I hope.
Although the system worked well as a process for decontamination of highly activated water, the real issue will be whether the system can be kept operation without remote maintenance. In my understanding, the contact dose rate of the water is as high as 1000 mSv. When the radioactive cesium is absorbed in the molecular sieve material, it should become highly radioactive. It is reported that the sorption materials should be exchanged every day by using a tong with a long handle. How much of worker dose will be from the maintenance activity is the most serious issue. Perhaps it may become necessary to choose either one of these two stages, Kurion’s or AREVA’s, in consideration of worker doses. In a reprocessing facility, for example, the dose rate is in an order that calls for some kind of remote maintenance provisions, I believe. With no time to provide such, it is likely going to become a real issue.
The processed water is planned to be stored in the tank yard being constructed. If the final radioactive concentration of the treated water achieved lower than the drinking water criteria, it may be able to be discharge into the sea, although this will involve much of political issues. Perhaps an independent verification might be needed to confirm the TEPCO’s claim for activation radiological assessment, if the environmental release is acceptable for the local community.
II. Recapping on air coolers for 1F1-4 spent fuel pools
After successful installation of the air cooler to1F2 SFP on June 1, TEPCO is planning to install a similar system to 1F3. Through their inspection by human entry as explained in Earthquke (92), they judged that it is not impossible to do this operation. The installation will start as early as on June 17. Similar planning is also projected for 1F1 and 1F4. In the former, the atmosphere of the Reactor Building is currently being filter cleaned. For 1F4, due to bending of the apparently Spent Fuel Pool Cooling and Purification piping, no planning has been released yet. I think the pipe should be OK considering the ductility of this grade of stainless steel, even it is bent. Just test by using a model pipe and see how bad it can be. We have to be concerned with worker dose budget distribution, instead of conservatism in the accident management.
Please visit http://www.tepco.co.jp/en/news/110311/index-e.html and see the video taken on June 9.
Result of radiation dose survey at reactor building of Unit 3 in Fukushima Daiichi Nuclear Power Station(ZIP 52.7MB)
(videoed on June 9, 2011)
III. Recapping on accumulation of “radioactive” sludge and ashes
I introduced this issue in Earthquake (95). Today a new guideline for disposal of “radioactive” sludge and ashe was released by the National Center of Counter Measures for Nuclear Disasters. For incineration of sludge, furnaces should have filtration to prevent releasing radioactivity. The sludge and ash should be kept in a shielded facility when the activity is higher than 100,000 Bq/kg. The way for ultimate disposal is being investigated. The lower activation wastes can be disposed in the municipal disposal facility with dose to the individual of the nearby residents will not receive more than 10 microSv/y, when the activity level exceed 8000 Bq/kg but less than 100,000 Bq/kg. For very low activation wastes, lower than 8,000 Bq/kg, can be used for land fill purposes, not for residence purposes, after water proofing.
IV. Recapping on removing contamination from 1F2 reactor building
The filtration system has been in operation since June 11. The aerosol concentration decreased by a factor of 10 for radioactive iodine and 4 for cesium. Since the contamination level is low, TEPCO intends to open the truck entrance door to improve ventilation.
V. Recapping on (3) Crippled “feed and bleed” operation
in Earthquake (95): Recapping on three months after the earthquake
On this issue, I received a comment from one of my colleagues and realized that I did not explain this issue well, resulting in some misunderstandings. Therefore let me add further explanation. First of all, the Fukushima Daiichi 1F1 unit has an unique design, even different from 1F2-4. Obviously this difference resulted in somewhat different accident sequence. On of the largest difference is in its “Shutdown Cooling System”, instead of the “Isolation Cooling System” used in 1F2-4. Attached please find an English translation of the corresponding illustration released by METI in:
(in Japanese, www.meti.go.jp/earthquake/nuclear/backdrop/pdf/04-accident.pdf ).
The “shutdown cooling system” is sometimes called “shutdown condenser” which takes the steam directly from the reactor pressure vessel, cooled through the heat exchanger as shown in the top illustration. It is necessary for the condenser to be fed with cooling water from the Reactor Component Cooling Water, from where the heat is released to the ultimate heat sink.
For water injection into the reactor vessel, as shown in the bottom illustration, there is a diesel-driven pump, which can take water from the filtered water tank and inject the water directly into the reactor pressure vessel. If this system worked even after arrival of the tsunami, this should have provided essential water for the “feed and bleed” operation.
To confirm this, I reviewed the list of major events of 1F1 during March 11 to 12. Let me extract some of the key issues below:
14:46 Seismic trip
14:52 14:52 Automatic IC start
15:03 IC stopped, manually re-started several times
15:07 PCV spray pump started started to cool suppression chamber (means water injection from S/P to the RPV?)
15:37 Station blackout
21:19 Preparing the diesel-driven fire fighting pump (D/D FP) to feed water to IC (indicating the shell side?)
21:35 Supplying water from D/D FP to IC
22:00 Reactor water level +550 from the top of the effective fuel (TAF) (this level agrees with my estimation)
00:30 Feeding water to the IC (shell side) through the fire fighting system
02:30 RPV water level TAF +1,300 (A) and TAF + 550 (B)
05:46 Pure water injection started by a fire engine
06:30 Completed injection of 2,000 liters through D/D FP line into Reactor Spray System (CS)
07:55 RPV water level TAF-100 to 200 (A) and TAF-100 to 200
07:55 Completed injection of 3,000 liter through FP line
08:30 Completed injection of 5,000 liter through FP line
09:15 Completed injection of 6,000 liter through FP line
09:15 Venting started
09:40 Completed injection of 21,000 liter through FP line
12:55 RPV water level TAF ミ1700 (A) and TAF-1500 (B)
14:53 Completed injection of 8,000 liter through FP line
15:36 Hydrogen explosion
19:04 Sea water injection (w/o boron) started
In all together, I presumed that the reactor core was in the water, even just at the bottom, until around 13:00 on March 12. During this time “feed and bleed” decay heat removal was maintained through Automatic Release and Safety Valves. The water injection was terminated for about 6 hours, until the sea water injection was started at 19:04. During this time, the fuels can be overheated. However, it is AFTER experiencing the hydrogen explosion. Therefore, I believe the root case of the hydrogen generation is more through radiolytic decomposition of water, instead of zirconium-steam reaction.
However, since 1F1 process computer went dead upon the station blackout and no data could have been recovered, the event sequence is much uncertain. In addition, there is a possibility that the RPV level gauges may not be showing the real values, due to a possible “internal hydrogen explosion”. I believe the “internal hydrogen explosion” occurred at around 23:00 of March 11, showing a high dose rates inside of the turbine hall.
Well, let me stop here today,
(Previous e-mail sent at 10:11 PM on June 15 as Earthquake (96))
I. Recovery of the secondary containment system for 1F1
This was announced yesterday but I was waiting for TEPCO to upload the illustrations. It is a kind of Fukushima version of the infamous Chernobyl “sarcophagus” and is called “cover” this time in Japan. Here it is. Please visit http://www.tepco.co.jp/en/news/110311/index-e.html and download http://www.tepco.co.jp/en/news/110311/images/110614_18.jpg as well as http://www.tepco.co.jp/en/news/110311/images/110614_22.jpg (You may be interested in other pictures as well, however, please be cautious in trying to open the first three large zip WMV files, since my computers, both Mac as well as Windows XP, froze by some reason. )
The cover is constructed with a light steel frame structure, 54 meters tall, covered with thin (1 mm thick) vinyl coated polyester sheets, such as used in construction of “Astrodome”. The construction will be performed by two shielded crawler cranes, with a capacity of 750 tons, without having assistance of workers for fitting prefabricated frames together. It was designed by taking a practice of traditional Japanese wooden houses, without using nails. The parts will be preassembled into 62 pieces at Onahama and shipped to the site by barges. It is scheduled to be completed by later September. Following 1F1, similar covers will also be constructed on top of 1F2 and 1F3.
II. “Designated evacuation promoting” spots
So far the national government has designated “scheduled (and organized)” evacuation zone, including Namie-machi and Iidate-mura, to reduce the radiation risks within accumulated radiation doses below 20 mSv/y. This concept was to prevent collapse the local communities by asking to evacuate the entire residents with the municipal districts. However, several regions also showed more than 20mSv benchmark around this zone, in particular Date-shi. In view of this situation, the national government has issued a new guideline to cover these spots by newly introducing the “designated evacuation promoting spots”. When such spots with the first year dose exceeding 20 mSv, first an investigation will be made to find whether the high dose rates can be reduced by cleaning diches or rain gutters, then estimate the exposure by hearing the life pattern of the residents. If evacuation is found necessary, the local government should be placed under Law of Rescue from Disasters and provide necessary assistance such as finding new lodgings and covered by the Nuclear Liability Law.
This is practical, if the local government can provide necessary administrative assistance. However, by consulting with the US DOER/NNEA dose maps, there hare many other spotty areas with the accumulated dose over 20 mSv/y level. Such a area can be identified beforehand. The government should be proactive to make these surveys by using these information.
III. Recapping on remediation of school grounds
On this issue, I have recapped in Earthquake (51), (58), (71) and (77) in the past. It was reported today that Fukushima Prefecture decided to decontaminate school buildings and strip the contaminated surface soil from all 193 school facilities, including day nurseries, kindergartens, grade schools, high schools and, this time, child care center after leaving school. They have to respond to the growing concern of the parents with the children. In connection with this, there is also a growing concern for internal exposure of young children living in Fukushima. Deep behind this, the resignation of Professor Kosaka, who was hand picked by the Prime Minister as a Special Counselor for the Center of Countermeasure for Nuclear Disasters, who appealed that the dose limit to the children should be much less than 20 mSv/y, typically 5 mSv/y.
On this issue, I doubt such measure is necessary, although the radiation exposure should be kept as low as reasonably achievable. The most significant exposure to the young children is from the radioactive iodine, the thyroid dose. According to the UNSCEAR 2008, Annex D, Health Effects Due to the Chernobyl Accident, more than 6000 cases of thyroid cancer cases observed among people who were children or adolescent at the time of the accident (by 2005, 15 cases were proven fatal). This effect was induced by the I-131 contaminated milk through meadow -> cow -> milk -> human food cycle, for which prompt countermeasures were lacking, resulted in large doses to the members of the public. Fortunately, at the time of Fukushima Daiichi accident, restriction of milk was made quickly. It is very unlikely that the thyroid cancer cases will be induced this time.
Well, let me stop here tonight!
(Previous e-mail sent at 0:42 AM on June 15 as Earthquake (95))
I. Recapping on the water purification system
After fixing all the problems encountered in the last few days, TEPCO started the pre-commissioning test by using a low level contaminated sea water. The test was started at 3:45 AM on June 14, to confirm the capacity of the second stage zeolile sorption stage, manufactured by the US Kurion, Inc. http://www.kurion.com/
The test was suspended at 2:00 PM today to check the DF achieved by this stage. Amazingly it worked! The DF for Cs-134 was 2700 and 3300 for Cs137. The highly contaminated water can mow be reduced to VLA waste water, so that the discharged water can be stored in the tank yard being constructed. The testing for the third stage, AREVA’s co-deposition process, will be started tomorrow. By shortening the original testing schedule one day, TEPCO intends to start commissioning on June 17, two days behind this critical schedule.
II. Accumulation of “radioactive” sludge and ashes
It is reported by NHK that a significant concentration of radioactivity is being detected in sludge and ashes from the municipal sewage treatment facilities. The radioactive sludge and ashes were detected in 16 of total 22 prefectures. The highest came from City of Fukushima, detecting 447 kBq/kg, followed with 55 kBq in Tokyo, 42.8 kBq in Maebashi and 26 kBq/kg in Utsunomiya.
The national government is asking to burn and store the sludge with contamination higher than 100 kBq/kg, until further guideline can be issued. Those prefectures detected radioactivity ranges widely, from Hokkaido to Osaka. Before the accident, frying ash was mixed with cement, however, cement companies refuse to accept when radiation contaminated, resulting is building up stored inventories as much as 50 tons a day.
III. Increased number of radiation workers exceeding 250 mSv.
Because of delay in assessing internal exposure measurement by using the whole body counters, those workers exceeding the limit of 250 mSv are increasing. Because of radiation health concern, the Ministry of Welfare and Labor is requesting TEPCO not to assign recovery work for workers whose internal doses exceed 100 mSv.
IV. Recapping on three months after the earthquake.
Since yesterday, I started to overview on why it is taking so much of time to put the Fukushima Daiichi under control, how to accelerate the recovery work and how we should be able to ameliorate the consequences. By looking into these points, I noticed that there are some very serious issues I have overlooked.
For example “station blackout.” In my understanding, the “station blackout” implies a total loss of emergency diesel generators, with battery power available as long as it lasts. However, I was shocked to find, in a METI report (in Japanese, www.meti.go.jp/earthquake/nuclear/backdrop/pdf/04-accident.pdf ), the following statement:
“At 15:37, due to the effect of tsunami, two 1F1 diesel generators stopped through flooding the pumps or electric panels of the emergency power buses, resulting in the “station blackout” situation. Similarly, the 1F2 also went into the “station blackout” situation, preventing power sharing between these two units.” It is questionable that the 6.9 kv emergency bus metal clad switch gears were flooded, since they are located on the ground level, according to the PSAR of 1F1-4. However, batteries could have been flooded, since it is also reported that they are installed on the basement of the turbine hall. In any case, if battery power was lost upon arrival of the tsunami in 1F1, it is impossible to control even the switch gears. This is not a “station blackout”, better to be called a “total loss of battery powers”. If that is the case, we have never looked into this kind of impossible situation.
In compared with this situation, all four units of Fukushima Daini did not experience the station blackout, since one transmission line was kept working. They were all brought to the cold shutdown state on March 14 for 2F1 and 2F2, on March 12 for 2F3 and March 15 for 2F4, after replacing submerged electric motors and installing temporary power using survived panels in the worst one. Also in 1F5 and 1F6, one diesel generator survived, since it was located in a higher location and was not flooded through the tsunami. All these plants were brought down to the cold shutdown state on March 20 for both 1F5 and 1F6.
Let me continue further.
(3) Crippled “feed and bleed” operation
In 1F1, with “total loss of battery power,” only remaining active capability for cooling the reactor core should have been “bleed” cooling by releasing steam through Release and Safety Valves. Their “release” function is lost without the battery power, however, its “safety valve” function should have worked at the set points of 78.0 kg/cm2-g (2 valves) and 78.7 (2 valves), releasing steam from the reactor pressure vessel into the Suppression Pool water. The “bleed” cooling is very efficient, while sacrificing the water level inside the reactor pressure vessel. A “back of an envelope” calculation showing the decrease in the water level versus time has already been presented as attached, indicating the cooling function of the reactor core should have survived for several hours. As a matter of fact, a RPV level gauge indicates the loss of water level at 6 AM on March 12. During this time, TEPCO operators were struggling to supply water to Emergency Condenser (IC) to the shell side, however, it appears that they were misled by being educated on importance of “cooling” function. The most effective cooling function should have been through “feed” water to the reactor pressure vessel. However, this was impossible without the battery power. At 5:46 AM on March 12, water injection was recovered by using a fire engine and successfully kept the core partially in the water. At 12:56 on March 12, the water level was ミ1700 mm (narrow range A) and ミ1500 mm (B). Therefore, in my assessment, it is likely that the reactor fuels maintained the “self-standing” capability at least until the hydrogen explosion occurred at 15:36 on March 12. At 19:04, sea water injection was started on March 12. The fuels may have been overheated without having steam supplied for about 6 hours. There is a possibility that hydrogen gas was generated through zirconium-steam reaction during this time period. Also, the hydrogen can be supplied by radiolytic decomposition of water.
Well, let me stop here tonight,
Date: Tue, 14 Jun 2011 00:31:59 +0900
Subject: Earthquake (94)
From: Genn Saji
I. Recapping on three months after the earthquake.
On this subject, I briefly introduced Japanese media reports in Earthquake (92). On this occasion, most news media issued a series of special feature of the consequence of the Higashi-Nihon (Eastern Japan) Great Earthquake series.
One issue I could not find at all was why it is taking so much of time to put the Fukushima Daiichi under control, how to accelerate the recovery work and how we should be able to ameliorate the consequences. Although these issues are too large to cover every aspects of the consequences, let me start overview some of the significant points, starting today.
(1) Totally unprepared for the “loss of ultimate heat sink (UHS)”
Because of the decay heat, it is indispensable to secure a heat removal pass from the nuclear fuels to the final heat sink, which is sometimes called the ultimate heat sink. The site selected for a nuclear installation should have a reliable long term heat sink that can remove energy generated in the plant after shutdown, both immediately after shutdown and over the longer term. Due to the tsunami, the Component Cooling Sea Water Pumps were all wiped out, cutting off the heat pass to the UHS. The pumps were located at +4.0 m above the average sea level, uncovered. The tsunami with the maximum height of 14-15 meters, submerged the pump below 10 to 11 meters of the tsunami water. Similarly, in Fukushima Daini, the pumps were located at nearly the same elevation, however, the pumps and final heat exchangers were protected with a water proof building.
The offsite power was recovered by 10 PM of March 11 for Fukushima Daini. The Fukushima Daini recovered decay heat removal capability on March 14 , after re-starting the pumps, and successfully brought all plants down to the cold shutdown state by March 15. This indicates that the Fukushima Daini survived from the loss of UHS for around 3 days.
During this period, there are no reports such as a series of hydrogen explosion as occurred in Fukushima Daiichi, although “abnormal increase in the containment pressure” was reported for 2F1 at 5:35 PM, as well as “loss of reactor cooling capability” announced at 6:49 PM, both of March 11, since TEPCO could not confirm availability of the sea water pumps. The 2F1-4 plants were all successfully cooled by injecting the suppression pool water by the Reactor Isolation Cooling System as designed. Compared with these successful experiences, the behavior of 1F1-4 is very strange. Why such difference occurred is a subject of further study, however, recovery of the sea water pumps brought the plants into a cold shutdown state within a day or so. This successful experience is being followed at Fukushima Daiichi for recovering its cooling capability, through installing alternative air coolers for the reactor containment vessel as well as spent fuel pools.
(2) Totally unprepared for “station blackout”
The tsunami wiped out all of the diesel powers which had successfully started upon “loss of off-cite power”. The reactors were automatically shutdown through the seismic trip signals. With the arrival of tsunami, Fukushima Daiichi lost all of the diesel power, resulting in a “station blackout” situation. Due to failure of all transmission lines by the earthquake, the off-site power was not available, until March 22, unlike in the case of Fukushima Daini. Although TEPCO appealed to rush 62 emergency power supply vehicles, only one of them worked due to differences of voltages. On top of that, the 1F1 and 1F2 batteries were installed at the basement and submerged under the tsunami water. Due to the station blackout combined with loss of DC power soon after the tsunami at 1F1 and 1F2, the operator control was severely restricted, since it was necessary to dispatch temporary batteries. In other words, 1F1 and 1F2 became out of control. The water injection function was lost, by losing the High Pressure Water Injection System in 1F1. Because of this, when comparing the timing of the large release events as recorded in the environmental monitoring data, there are several events that do not match any operator actions starting March 12, after the first hydrogen explosion.
II. Detection of strontium in sea- as well as underground water
In the last two days, TEPCO started to release concentration of Sr-89 and Sr-90 in sea water as well as in underground water sampled on 16 May. This delay is because it takes at least 3 weeks for the assessment of these beta-emitters. In general, release of these “intermediate” species is much higher in the down stream of leakages from the containment vessel, compared with leakages in the form of aerosol later deposited on the ground. It is because of the decontamination effects of the pool water of the containment vessel. Therefore, more attention is necessary for sea water contamination in the case of strontium. Using these data, the updated release fraction summary table is attached. Here I noticed a serious issue, an immobility of strontium compared with cesium, the latter seems to be more easily dispersed. In the attached update, please compare the release rate of strontium computed on April 18 (Table 3/4) and May 16 (Table 4/4). In the latter, the release rate of Sr-89 and 90 as computed with ratios to Cs-137, after making the core inventory correction, increased by an order of magnitude in one month. This should indicate that the strontium isotopes may not disperse so easily as compared with cesium. The strontium should contribute more persistently in marine food chain. Therefore, more attention should be paid for strontium.
III. Sea water decontamination unit started operation
Today, TEPCO announced that the zeolite loaded decontamination unit, for cleaning of 60 tons of sea water per hour, was started in service. However, its decontamination capacity was disappointingly low, with only 20-30%, much less than the projected goal of 60-70% reduction in cesium concentration. TEPCO is planning to add another filter layer to remove potential oil contamination.
IV. Recapping on troubles fixed in the water purification system
Although the mechanical troubles are all fixed, the pre-functional test has not been initiated yet. This test will use low level contaminated water to obtain data of DF in each stage. As of midnight of June 14, the test has not started yet. With daily increase in the volume of the highly contaminated water, the situation is very critical. It is reported that the highly contaminated water may start overflowing from the pit as early as on June 20.
Well, let me stop here tonight,
(Previous e-mail sent at 11:01PM on June 12 as Earthquake (93))
I. Troubles fixed in the water purification system
Another issue was identified but fixed later today in the critically awaited water purification system. The manufacturer of the system fixed as many as 48 leaking valves, flanges as well as some error in the computer system. However, they found that the sea water flow of one of the 4 loops of the “zeolite” sorption system, with a total capacity of 50 tons per hour, appears to be plugged, since only 0.5 tons was found flowing through. With one loop not available, the capacity will be down to 75%. However, early this evening, this trouble disappeared also, the trouble identified due to a new and sticky valve.
This stage was supplied by US Kurion, Inc. http://www.kurion.com/
The company says that more than 100 tons of its unique patent-pending Ion Specific Media (ISM) is available to assist in the cleanup of contaminated liquid from the Fukushima I Nuclear Power Plant. The ISM base material, now exclusively distributed by Kurion, was successfully used to cleanup liquids from the Three Mile Island (TMI) nuclear plant accident. They further says that the use of salt water for emergency cooling at Fukushima “blinds” conventional organic ion exchange resins used for decontamination. “Because Kurion’s inorganic Ion Specific Media works as a molecular sieve and adsorbent versus the ionic exchange process with resins, its extraordinary performance as an isotope sorbent in aqueous solutions is not negatively impacted by salt water and other common interferents. Lastly, it had to be “vitrification-friendly” in the sense that it could withstand the melting process without degradation and associated isotope/off-gas releases; attributes not possible with ion exchange resins.
Well. Everyone is waiting for this system to be effective, with fingers crossed.
II. Recapping on the 1F4 pool water studies
On this issue, I have been doing some scoping radiation chemistry calculations looking for possible clue in the hydrogen explosion. I am very much encouraged to find that there are some specialists started to look into this issue from a point of view of radiation chemistry. Especially Dr. Sergey A. Kabakchi of Kurchatov Institute of Atomic Energy, has a wide experience of calculations of consequences of influence of the radiation on aqueous systems in normal and emergencies. For further studies, he requested me to compile a set of plant data. This motivated me to look further into the root cause of the anomalous hydrogen generation and release, very closely related with boiling. Attached please find my compilation of the 1F4 spent fuel pool data for scoping calculation purposes. By developing this data, I came to the following accident scenario.
(1) The “station blackout” induced termination of water circulation, cooling as well as purification of pool water.
(2) The spent fuels resulted in natural convection heat removal mode with the pool water flowing from the bottom at a reduced flow rate, determined by the decay heat and heat balance. The dissolved oxygen (DO) was supplied from the natural convection flow. The concentration of DO should have been determined at the surface of pool water exposed to air atmosphere. The hydrogen generation, through radiolytic decomposition of water, continues but was relatively suppressed due to reverse oxidative radical reactions.
(3) The temperature of the pool water started to increase. With the reduced flow rate, nucleate boiling should have started by using the dissolved hydrogen as nucleus. The steam bubbles are started to be released, when the pool water temperature reached somewhere around 70-90 degreeC.
(4) With initiation of boiling, the flow rate through the fuel assemblies drastically went down, due to very high boiling heat transfer rate. More than an order of magnitude reduction is predicted compared with a single phase natural convection.
(5) With decreased flow rate, the DO concentration goes down, reducing the reverse oxidative reaction channels. This resulted in larger hydrogen generation rates.
(6) The steam bubbles also striped hydrogen gas accumulated in the bulk of pool water and released to the Spent Fuel Handling Room.
(7) The steam was condensed in the wall and hydrogen gas was gradually accumulated.
Although more detailed thermo-hydraulic natural convection assessment is desirable, it is anticipated to be much difficult to find exact data, since we were paying not much attention to the radiolysis in the spent fuel pools and there are not sufficient instrumentation data available for further scientific studies, I am afraid.
Well, let me stop here,
(Previous e-mail sent at 0:50 AM on June 12 as Earthquake (92))
I. Three months after the earthquake.
On this occasion, most news media issued a series of special feature of the consequence of the Higashi-Nihon (Eastern Japan) Great Earthquake series. All pointed out that the recovery activities are very slow. Most of them pointed out that delay in disposal of tsunami debris is one of the biggest obstacle for recovery operation. In addition, 91,000 people are still in refuges. Although 28,700 temporary housings have been completed, only 17,000 of them are occupied. For evacuated people, some of the temporary housings are located in inconvenient places, nor necessary social infrastructure has not been recovered yet. For example, as many as 57, 900 houses are not provided with the city water service yet. More serious issue is nearly a half of the evacuated people became pessimistic for returning to where they have been living.
From this point of view, there is no prospect in sight in the planning for recovery and resettlement of the evacuated zones.
In the “emergency preparedness” zone, there are 153 industrial facilities, in which no one has prospect for re-opening. Everything depends on when the damaged plants became under control. From this point of view, increased number of workers are getting out of condition due to working in air tight radiation protection suits in hot weather, such as due to dehydration. The improvement of working environment is becoming an urgent issue and some rest areas have been constructed. They are now provided with a pack of refrigerant. During the hot season, there will be a rest hours in the hottest afternoon hours.
The total volume of the highly contaminated water continues to be increasing. The pre-functional test of the new water purification system has not been started yet, due to miniscule leakages at the zeolite sorption stage. The leaky valves and flanges have been ameliorated by putting sealing compounds around the joints. This can be seen in the updated set of photos uploaded by TEPCO: http://www.tepco.co.jp/en/news/110311/index-e.html please visit “Coupling Parts of Inlet and Outlet of Cesium Adsorption Tower (pictured on June 9, 2011)”
http://www.tepco.co.jp/en/news/110311/images/110611_02.jpg shows a side view of this facility.
II. Recapping on removing contamination from 1F2 reactor building
In 1F2, the moisture level is as high as 99.9%. Combined with the high dose rate, the worker entry is greatly restricted. In view of this, TEPCO has started to decontaminate the room air by employing the heated filtering system used in entering into 1F1 by improving to add heaters. For that the double doors from the turbine building has been opened at 12:39 on June 11. After a few days of operation, they plan to open the truck entrance door, facilitating the natural draft ventilation. By opening the door, some contamination may also leak out to the environment. By exchanging the room air by natural ventilation, TEPCO hopes to allow the worker entrance.
TEPCO uploaded a series of photos in their website: http://www.tepco.co.jp/en/news/110311/index-e.html
This is the first time that a set of relatively clear photos became available inside of this building. The photos were shown in *pictured through vinyl which covers the camera on June 11, 2011”.
http://www.tepco.co.jp/en/news/110311/images/110611_08.jpg shows the temporary intake air duct for filtering air.
http://www.tepco.co.jp/en/news/110311/images/110611_09.jpg shows the air cleaning units installed inside of the turbine building.
http://www.tepco.co.jp/en/news/110311/images/110611_10.jpg shows temporary air duct laid down
http://www.tepco.co.jp/en/news/110311/images/110611_11.jpg shows the air cleaning units installed inside of the turbine building
In Unit 2, the air cooler has been installed and working for the spent fuel pool.
III. Recapping on inspection of 1F3 reactor building.
Also, http://www.tepco.co.jp/en/news/110311/images/110611_001e.pdf is showing a map of radiation level data taken along the route of the inspection, http://www.tepco.co.jp/en/news/110311/images/110611_06.jpg is showing that the dose rate was higher near the large machine hatch. http://www.tepco.co.jp/en/news/110311/images/110611_07.jpg shows that the water treatment skid may not be accessible for workers for piping.
IV. Recapping on inspection of 1F4 reactor building.
A set of photos taken by entering into the 1F4 is also uploaded in the TEPCO website. The “4th Floor of Unit 4 Reactor Building (pictured on June 10, 2011) Pictured at South Side on 4th floor of Unit 4 Reactor Building”
http://www.tepco.co.jp/en/news/110311/images/110611_04.jpg is showing that a part of the piping of Spent Fuel Cooling and Cleaning System is bent, perhaps may not be usable for installation of the air cooling system.
http://www.tepco.co.jp/en/news/110311/images/110611_05.jpg, “4th Floor of Unit 4 Reactor Building (pictured on June 10, 2011) Pictured at South Side on 4th floor of Unit 4 Reactor Building” is showing severity of the hydrogen explosion in this building.
Well let me stop here.
Date: Sat, 11 Jun 2011 00:22:02 +0900
Subject: Earthquake (91)
From: Genn Saji
I. Disposal of the contaminated tsunami debris
Yesterday, I touched on the anticipated difficulties for ultimate disposal of highly radioactive wastes to be released from the new water purification system. In parallel with this, a huge amount of tsunami debris is left in the shore line of the Fukushima Prefecture. Currently the contaminated debris have been moved to 117 temporary depositories, where radiation levels are being monitored. So far two of them with minor contamination were allowed to be disposed by using ordinary incineration facilities. The Ministry of Environment (ENV) is investigating possible radiation effect of disposing these by constructing a special waste incineration facility, where exhaust filters will collect flying asses. Through this process radioactive ashes will be generated, for which an ultimate disposal facility will become necessary. ENV sounded to the Fukushima Prefecture Government, however, the Governor responded with a flat rejection, by saying that nuclear energy policy should need more in-depth thought. Now it is increasingly becoming a political issue how to dispose the Fukushima Daiichi waste in the near future as well as those left within the 30 and 20 km zones. The debris within these zones have been left untouched, preventing recovery from the tsunami damages. The approach made by ENV was also poor. The way they explained to the Fukushima Prefecture does not convey that the Government is thinking of true welfare of the affected people. The most critical issues should be how to ameliorate land, for future resettlement, within the “scheduled (and organized)” evacuation zone, “emergency preparedness” zone as well as the 20 km “vigilance (off limit)” zone. Where such studies are being made in the Government is not visible for the affected people.
II. Recapping on two TEPCO operators found received excessive internal radiation exposure
On this issue, I introduced in Earthquke (80) . (81) and (84). Further detailed inspection now concluded the accumulated doses as below.
identification approximated age accumulated doses (mSv)
MaleA >30 678
MaleB >40 643
Approximately 80% of their doses are reported to be due to internal exposure through inhalation pathway. If we assume a tissue weighing factor of 0.05, an estimated thyroid absorption dose should be around 12 Gy, since the external doses were 74/89 mSv. In the UNSCEAR 2000, there is no risk factor estimated for adults from the data obtained through the Chernobyl accident. If we use the risk for children 0-18 years old, the excess absolute risk for the thyroid dose group of >2 Gy was 2.4/(10000 PY Gy). Since this risk factor is obtained by the epidemiological study and may not be appropriate to apply to this situation. Although it is reported that there will be no health effect, I think they need to be kept under medical monitoring, since 12 Gy of thyroid dose is at a high level, although no thyroid cancer was reported among adults at the time of the Chernobyl accident. It is reported one additional worker may have received high internal doses.
III. Recovery of the off-site environmental monitoring station.
Before the accident, the environmental monitoring around the Fukushima Daiichi and Daiini has been surrounded by 23 monitoring stations. Because of the tsunami, all of them went down except for just one. Fukushima prefecture successfully restored 8 of them, by entering into Nuclear Energy Center, which is located within the “emergency preparedness” region. All of the monitoring data have been processed by a computer system located in this center. They crew will try to recover remaining 11, although last 4 have been devastated by the tsunami.
IV. Recapping on water purification system completed
TEPCO announced today that the pre-commissioning test is being delayed since they discovered small water leaks from valves and joints from as many as 10 locations. The test was conducted by using sea water. These troubles will be repaired tomorrow and may be able to go into the test very soon.
Well, let me stop here. Today I went out to pickup my 29 months old grand daughter from her day nursery and a bit exhausted since she insisted to play tag for more than an hour at a park near by. I cannot cope with her vitality.
(Previous e-mail sent at 10:53 PM on June 10 as Earthquake (90))
I. Water purification system completed
TEPCO announced today that installation of the highly waited water purification systm was completed and ready for pre-service test. The system is constructed at the Centarized Waste Processing Facility. TEPCO plana to test the system for a week, for the targeted commissioning date of June 15. Although the most recent photos has not been released yet, an outline of the system has been posted in the TEPCO’s website as attached. http://www.tepco.co.jp/en/news/110311/images/110604_outline.pdf
The system has a capacity of 1200 tons a day hoping to achieve a DF of 1000 to 10000. As can be seen from the attached outline, the first stage is for removing oily inclusion, followed with a zeolite sorption stage for cesium and iodine and the third stage is co-precipitation for removal of cesium and strontium and then comes a reverse osmosis stage to finally distillation stage. The sorption material will be supplied by the US Clion Co. Many people are crossing their hands that the system works as intended. However, there are many unresolved questions whether the system works as intended. The first issue is in the high salt concentration came from the sea water injection, as well as sea water left behind the tsunami. In March, many chemists in Japan looked for zeolite which may show high DF in the salt water, only to confirm the DF of 10 at most. Also a group of Russian scientists tested layered hydrazinium titanate (LHT-9), which also showed no much better than zeolite in sea water, even though it showed sorption capabilities in wider nuclear species. As a matter of fact, TEPCO is going to use a zeolite water purification system to reduce the activation of the sea water by 60 to 80 % for Cs-137.
Also it has not been reported that the AREVA’s co-precipitation process works in the salt water. Professor Ohta of Kanazawa University has also developed a much better chemical, although it is not reported whether it works in the sea water. ( http://jp.wsj.com/japanrealtime/ )
The situation of accumulation of contaminated water continues to be urgent in all of the Fukushima. TEPCO is requesting for a permission of releasing 3000 m3 of sea water left behind by the tsunami from Fukushima Daini. They plan to release slightly contaminated water, after decontaminating it to the level specified by the nuclear safety criteria. They plan to used a temporary decontamination facility with a capacity of 30 tons?an hour. ?However, Mr. Tsutsui, Vice Minister of Agriculture, Forestry and Fishery (MAFF), flatly refused to accept by saying it will induce hearsay damage.
Even when everything turned out to be successful, the waste disposal should also a problem, Currently as much as 105,000 m3 of the highly contaminated water is estimated and the total volume of the contaminated water may reach 200 thousands tons. As much as 500 tons of water is injected into the reactors. In the beaker tests, the liquor to the sorption material ratio was around 100. This indicates that as much as a few thousand tons of contaminated sorption materials can be generated. The resultant waste disposal issues must be investigated from now on. Since cesium is a volatile species, the waste gas generated from the ceramic process may not be feasible. Perhaps one of the most practical solution is just bury into a layer of bentonite (cray), after putting the sorption materials in metallic containers, in the medium depth of soil. It is anticipated to be a big political problem to find a waste disposal site. I envision to request to Fukushima prefecture to accept construction of such a disposal site in the already highly contaminated zone in Fukushima to dispose all other surface soils in that area eventually needs to be disposed.
II. Inspection of 1F3 reactor building.
After completing removal of debris around 1F3, 11 TEPCO team went inside of the reactor building first time after the hydrogen detonation for about 20 minutes. They measured doses as well as inspected the status of piping which they plan to use for injection of nitrogen gas into the containment vessel. TEPCO plans to install air cooler to cool down the reactor vessel.
III. Detection of strontium beyond 30 km region.
NEXT announced that a small amount of strontium was found at 11 sampling points 60 km from the Fukushima Daiichi, although strontium has been detected within the 30 km region. The surface contamination level is approximately 1/1000 of Cs-137. The release fraction of strontium is much less than the case of Chernobyl accident, where approximately 80 PBq of Sr-89 was released together with 74-85 PBq of Cs-137, according to UNSCEAR 2000, Annex J: Exposure and effects of the Chernobyl accident. Apparently, this large difference comes from the difference in release mechanism between these two accidents. The strontium release from the Fukushima Daiichi is due to the release of the contaminated steam from the containment vessel, after being decontaminated by the suppression pool water. Whereas in the Chernobyl accident, a significant portion of the reactor materials were discharged directly through steam explosion. I do not think this observation support the early melt through scenario as being concluded by TEPCO in their recent analyses.
Let me add one episode. When studying the land contamination sampling data containing strontium, I noticed a local hot spot of Ag-110m (half time is 250 days). It appears that some fuel particles may exist in these sample, since strontium as well as silver is the “intermediate” species, some very small amount of fuel materials may have been released together with the contaminated steam.
Well, let me stop here,
(Previous e-mail sent at 00:13 AM on June 9 as Earthquake (89))
I. IAEA Ministerial Conference
On June 7, NISA posted the following report for the IAEA Ministerial Conference to be held on their website
Report of Japanese Government to the IAEA Ministerial Conference on Nuclear Safety - The Accident at TEPCO's Fukushima Nuclear Power Stations - http://www.kantei.go.jp/foreign/kan/topics/2 01106/iaea_houkokusho_e.html
This document is an English translation of the Japanese version. Unfortunate4ly, the translation seems to have not been completed as of this morning. Therefore, some of the later additions, such as the section of “meltdown” analyses, contained only a summary section in the English version. By quickly glancing through the document, this document is for the ministerial meeting and is not for specialists. It is written by the bureaucrats of the relevant ministries, headed by Mr. HOSONO, Gowashi, Assistant to the Prime Minister. It is reported that he requested the ministries to rewrite many times, to reflect the direction provided by the Prime Minister. It also contains 28 lessons learned, which has been immediately used to order, by MEXT, to all of the power companies to report how they will try to implement by June 14. Although most of the lessons learned are reasonable, however, many of them are not easy to implement in the current nuclear reactors in Japan. For example, independence of layout for reactors are requested, however, this may imply that the half of the current fleets should not be able to be operational. Although the Prime Minister has been saying that, except for the Hamaoka NPPs, all other fleets should be kept in operation, the local residence is reacting “not to allow unsafe NPPs”, making local government in a difficult situation in permitting them to restart. Currently many NPPs are in the scheduled shutdown to be prepared for summer peak electric power demands. However, they have not been able to restart in the wake of the anxiety of the local residents.
In view of the nature of this report, the contents may not be satisfactory for specialist people, nor it contains detailed engineering data necessary for independent verification. Perhaps your should wait for the Prime Minister proposed international nuclear safety specialists meeting to be held later next year.
Let me stop here.
Date: Tue, 07 Jun 2011 23:28:47 +0900
Subject: Earthquake (88)
From: Genn Saji
I. Comments on recapping on the 1F4 water radiolysis studies by Prof. Bartels
Professor David Bartels, Notre Dame Radiation Lab and is one of the authors of the data for radiation chemical studies (AECL 153-127160-450-001), commented by saying “Your calculation of H2 produced by radiolysis is just wrong, if you are assuming pure water with ca. 1e-4M dissolved O2 as the starting point. Something is very wrong with your solution of the steady state concentration. It makes no sense that there would be a sudden jump at 40-50C....We do need to account for H2O2 decomposition on the surfaces.ロ・he dissolved O2 is probably too high, once the pool gets close to boiling. We have omitted dissolved CO2 which could change things a bit, as well as other impurities. And there is certainly a gradient of the radiation field. But I think the most important thing is the boiling. Once boiling is possible, probably on the surface of the fuel rods, there is a mechanism for the H2 (and O2) to separate into the gas phase bubbles, which destroys the steady-state as calculated above. This was nicely demonstrated by the recent experiment of Katsumura-san.
He provided me a set of calculation results, by solving with a Gear integrator. I have been checking my computer tool to benchmark with his results. There are some difference in the temperature dependence between these two and I am investigating the cause of the difference. However, his comments are useful to explain the difficulties in applying the radiation chemical methodologies for the spent fuel situation. That is the extremely long time scale necessary for computation by incorporating the natural convection. In the infamous NC model I have used, the ‘residence time,” a duration of the water entered from the bottom of the fuel assembly to the top, ranges from 1000 second to 10000 seconds. During that time the water is keep being irradiated. The initial dissolved oxygen, for example, can be burn out before reaching to the exit of the fuel assemblies. When such a situation occurs, the reverse reaction so far preventing hydrogen generation can be lost, resulting in an high hydrogen release rate. Considering the burn up, I think the QSSA (quasi steady state approximation) should also be a feasible approach, since the time dependency can be expressed by the resident time. However, disadvantage is in the need of more rigorous material balances.
The computer code solved a set of reaction kinetics system with a wide variety of characteristic times varying as large as ten orders of magnitude, with the concentration variation often 20 orders of magnitude difference.
II. Update of the hydrogen generation by NISA.
NISA people seem to be occupied in preparing presentations for the coming IAEA Ministerial-level meeting soon to be held during June 20-24. For last several weeks, many of the previous NISA releases are being updated. This include the amount of hydrogen generation along their melt down scenario.
Unit Hydrogen Generation (kg)
1F3 750 + 100
Also, a few days ago, it was reported that the severe explosion in 1F3 was due to hydrogen detonation, whereas deflagration for 1F1 and uncertain whether it was a hydrogen explosion in 1F2.
III. Special Committee for investigation of nuclear disaster
The first meeting was held today by the Special Committee for investigation of nuclear disaster, which was convened by the prime minister. They will investigate the Fukushima Daiichi accident digging deep into the causes of this accident not only from a technical point of view, but also the societal background. The chairman of this committee is Youtaro Hatakemura, Professor Emeritus of Tokyo University. He is a famous person by proposing “sippaigaku” (failure-cology) in his data base of lessons learned from failure experiences. In their first meeting, they decided to consider the Fukushima Daiichi as an “organizational accident” as proposed by James Reason, 1997. Managing the Risks of Organizational Accident, Ashgate Publishing Limited. They plan to complete an intermediate report by the end of this year, to be followed with the final report after controlling this accident. The prime minister himself will be the subject of their inquiry. They also investigate the Japanese regulatory system from the time it was formulated. The committee members consist of specialists of diverse arena, including former supreme court justice, IAEA ambassador, writer, radiation safety specialists, etc.
Well, let me stop here tonight.
(Previous e-mail sent at 2:27 AM on June t as Earthquake (87))
I. Recapping on the 1F4 water radiolysis studies
The trial calculation (III) attached two days ago seems to have attracted an interest and I received a few questions and comments. In order to respond to these, attached please find an update. The largest point in update is to restrict the dissolved hydrogen concentration not to exceed the solubility limit. This is equivalent to increase concentration of DO as well as oxidative radicals that enhance reverse reaction for hydrogen generation. As anticipated, it resulted in a significant reduction of hydrogen generation. At this stage, effect of boiling is not clear. It should be a higher priority issue.
II. NISA released their meltdown calculation
Today, NISA released their calculation to estimate the initiating time of melt down. The results are summarized below.
Unit Approximate time of RPV failure
1F1 8 PM of March 11
1F2 10:50 PM of March 14
1F3 10:10 PM of March 14
It is reported that these results will be presented at the coming IAEA ministerial level meeting.
Their results are certainly conservative, by totally ignoring the effect of “feed and bleed” operation, for that purpose ECCS is integrated into the plant, including Pressure Release and Safety Valves, Isolation Cooling System and High/Low Pressure Injection System. Even under the “station blackout”, most of them worked as designed, using the battery power, although heat removal was not possible due to the “loss of ultimate heat sink.”
III. Planing to remove moisture from 1F2 reactor building
In 1F2, the moisture level is as high as 99.9%. Combined with the high dose rate, the worker entry is greatly restricted. The air sampling has shown the following activity concentrations (Bq/cm3): I-131=4.2E-02; Cs-134=5.8E-02, and Cs-137=5.6E-02. In view of this, TEPCO plans to remove moisture by employing the filtering system used in entering into 1F1. Honestly speaking, I do not understand whether the filters are any good for removing moistures. If we assume the total volume of the building as large as 2E+05 m3, the total amount of moisture need to be removed is as large as 10 tons. What they need will be huge dehumidifiers. However, I suspect that the moisture should be coming from cracks in the primary pressure boundary or containment vessel. Without stopping the leak source, it should be very difficult to improve the working environment.
IV. Removal of debris around 1F3
TEPCO has been removing the highly contaminated debris scattered around 1F3. So far they removed debris to fill 250 containers, employing remote controlled power shovels. However, there still remain some hot debris with a dose rate of around 1 Sv/h. Removal of hot spots are still necessary to improve the working environment.
V. Off-site center did not function
The off-site center was supposed to become a control tower of global accident management, however, it failed to function due to the earthquake damage, loss of power, in sufficient air cleaning capability, failure of communication network, etc.
Well, let me stop here.
(Previous e-mail sent at 9:02 PM on June 5 as Earthquake (86))
I. Recapping on installation of a new pressure gauge
I introduced this issue in Earthquake (83). One of the most troublesome issues is that, due to the “station blackout”, the central control panels went out when battery power was exhausted around the midnight of March 11. Although the control room operators struggled to make some of the essential instrumentation and control channels recovered by calling for dispatching auto batteries, however, many of the instrumentation showed questionable readings, especially those using Burdon pressure elements, such as pressure gauges, differential pressure level gauges as well as differential pressure flow gauges. Many of these gauges are using three-fold redundant common instrumentation pipes. In particular the top level pipes provide the reference pressure of the reactor vessel. In all of 1F1-3, there occurred events where the reactor pressure readings suddenly dropped and after that all of the readings started to show strange results. Since these event induced these events simultaneously in each unit, I have been suspecting that “internal hydrogen explosions” occurred as preceded by the Hamaoka Unit 1 hydrogen explosion/pipe rupture accident as introduced in Earthquake (69) by an one page summary in English. Without this failure, sufficient amount of water injection could have been possible, resulting in a cold shutdown state much earlier, I believe.
prevent buckling due to cool down inducing vacuum.
II. Plutonium first detected offsite
It was reported today that a trace amount of plutonium was detected at Ookuma-cho, 1.7 km from the Fukushima Daiichi, detected the first time off-site. The amount detected was 0.78 Bq/kg of soil for Pu-239+240. Although the concentration is at the same level as being detected in the Japanese territory due to the fallout from nuclear weapon tests performed in the past by other countries, it was concluded to be released from the Fukushima accident, since the isotopic composition was different.
III. Recapping on the continued threat of leakage of rain water into the buildings
I introduce this issue repeatedly, the last one in Earthquake (81). Due to the continued water injection, as much as 500 tons of water volume is continue to increase, not including the rainwater nor the underground water. The TEPCO was predicting that the trench water may overflow as early as in June 20. In view of this urgency, TEPCO decided to increase the storage capacity of the water-proofed Centralized Waste Processing Facility by 1500 tons. Since June 4, TEPCO re-started to pump the highly contaminated water at a rate of 24 tons an hour. This operation is reported to be successful in preventing further increase of the 1F2 water level in the basement as well as its trench.
Well, let me stop here today.
Date: Sat, 04 Jun 2011 22:27:25 +0900
Subject: Earthquake (85)
From: Genn Saji
I. Recapping on the 1F4 water radiolysis studies
Being motivated by the Prof. Y. Katsumura’s rapid experimental test (as introduced in Earthquake (80)), I could complete a detailed water radiolysis assessment to find the root cause of hydrogen generation as attached. The assessment was performed by integrating a simple natural circulation flow through the spent fuels in the 1F4 SFP water. The estimation of the flow rates through the spent fuels became necessary to compute a residence time of irradiation of the pool water when going through the fuel assemblies. Since the residence time of the reactor water during the full power is in a order of one second or so, this flow rate should be much lower, proportion to the decay heat ratio which is only P/Po = 3.4E-04 at the time of the 1F4 accident. As a matter of fact, the flow velocity calculated from this model is around this value.
The results are shocking for me. There exists a “quasi equilibrium state” below 50 degreeC, where the dissolved hydrogen (DH) is less than the solubility limit of the hydrogen gas in the water. Above this, the DH concentration becomes higher than the solubility limit and should start hydrogen gas release from the spent fuel. When this information is converted to the hydrogen release rate, as much as several thousand STD-m3/day of hydrogen gas can be easily generated when the pool temperature is over 80 degreeC.
The lessons learned through this exercise can be summarized as below:
1. Due to the “station blackout”, the circulation of the SFP water was terminated. The resultant long residence time of water inside the spent fuels, through natural circulation, induced a rapid removal of oxidative radicals, resulting in termination of the reverse reactions so far restricting the hydrogen generation.
2. When the DH concentration exceeded the solubility limit, a substantial hydrogen stared to be released.
3. The increase in the pool water temperature induced higher natural circulation flow, resulting in higher rate of hydrogen gas transfer from the irradiated region.
4. With a rise in the temperature of SFP water, the DH is released to the Fuel Exchange Room with steam bubbles. The steam was condensed in the wall of the room, separating the hydrogen gas.
According to this modeling study, it is essential to keep the SFP temperature below 50 degreeC, under which a “quasi equilibrium condition” can be maintained to prevent extraneous hydrogen gas generation. This threshold value may change depending on the decay heat level. The plant operator should have this kind of results to be prepared for severe accidents.
This calculation should be benchmarked by other institutions independently, since errors are easy to slip in, due to complexity of the chemical kinetics equations and rate constants. I believe this is a pretty good topic for an international benchmark exercise, in view of the safety implication of the SFP in an event of “station blackout.” Also, some test should be performed to confirm this mechanism, including the flow velocity of water in the spent fuels.
It should be fare to add that the current TEPCO position is that the 1F4 hydrogen explosion is due to in-flow of hydrogen transported through a common ventilation duct due to venting. One of the biggest difficulties of this hypothesis is in the fact that there is no way to estimate an amount of hydrogen gas generation as well as transport of the gas through the common ventilation duct. However, TEPCO withdrew this claim today, since one of the double valves should have been fail closed upon loss of DC power.
II. High dose rate steams found by “PackBot” inspection
A video taken by “PackBot” is posted in Confirmation of steam situation at a reactor building of Fukushima Daiichi Nuclear Power Plant Unit 1 (ZIP 5.55MB) of http://www.tepco.co.jp/en/news/110311/index-e.html . The steam is leaking from a penetration of piping through the floor level. It is reported that the dose rate around this penetration is as high as 3000-4000 mSv/h. By consulting with the PSAR, the location is where pipes from the suppression pool are led to ECCS. I further intensified my suspicion that there should be a pipe damage in this pipe, due probably to the “internal hydrogen explosion,” although TEPCO is relating this to their meltdown scenario.
III. Outline of contaminated water processing facility
Please visit http://www.tepco.co.jp/en/news/110311/index-e.html to download Fukushima Daiichi Nuclear Power Station Outline of water processing facilities (PDF 70.1KB)
Also today, transportation started for additional tanks for storage of contaminated water. The “Tamada” Industries manufactured 170 tanks of 120 m3 capacity and 200 with 100 m3 capacity, totaling to 40,000 m3. The basic sizes for 120/100 tons tanks are: height 3.7/3.4 m, length 15.1/13.5 m and weight 15/13 tons. They are steel tanks with the wall thickness of 9 mm, covered with re-enforced plastic linings of 1 mm inside, 1.8 mm outside.
Well, let me stop here today.
(Previous e-mail sent at 00:06 AM on June 4 as Earthquake (84) (Earthquake (83) should have been (84))
I. Strategy for storage of the contaminated water
According to the TEPCO’s recent estimation, the overview of the highly contaminated water is as summarized below.
1F1 16,200 tons
Centralized Waste Treatment Facility 13,3300 (transferred mainly from 1F2)
Total 105.100 (with a total activation of 7.2 PBq)
Currently the new onsite water treatment facility is scheduled to become partially available on June 15. Without this, the water may overflow as early as in June 20. With this facility, TEPCO plans to decontaminate the water to a mid to low level waste water and store them in the tank yard being constructed. (Although definition of the waste management levels is not disclosed,according to the reprocessing practice, MA/LA correspond to 10/0.18 TBq per m3, indicating that TEPCO seems to be anticipating a modest DF.) In addition, TEPCO plans to construct an underground emergency tank for HA water storage, targeted to be completed in August. They are working hard to increase a margin urgently needed. One action was to transfer the water in the basement of 1F3 turbine hall to its condenser well of the turbine.
II. Recapping on Two TEPCO operators found received excessive internal radiation exposure
On this issue, I introduced in Earthquke (80) and (81). Further detailed assessment revealed that the their 50 year life span accumulated thyroid doses may reach 210-580 mSv for the worker at the age in 30th, 200-510 mSv for the worker at the age in 40th. These internal doses should be added on top of the external exposure of 74/89 mSv. Although their thyroid doses are high, however, considering their age, the health effect should be very small, comparing with the case of the Chernobyl accident, where much higher thyroid doses were accumulated through pasture -> cow -> milk -> infants food chain. In addition, the thyroid of the Japanese people are generally saturated with stable iodine, through our habit of taking a lot of sea food. There are practically no iodine deficiency case in Japan.
However, there is an increased concern that internal exposure measurements have not been performed for thousands of workers, due to the limited availability of whole body counters. Only 1400 workers have gone through this examination.
Well, let me stop here today.
(Previous e-mail sent at 11:43 PM on June 2 as Earthquake (83))
I. Recapping on the continued threat of leakage of rain water into the buildings
With arrival of the rainy season, the effect of rain water as well as underground water is becoming continued threat to all units. Today TEPCO introduced the tank yards for 1F5 and 6. Please visit Fukushima Daiichi Nuclear Power Station Temporary storage tank (for the purpose of low level radioactive materials in Unit 5 and 6) installation status
Place: Storage Area (North Side) http://www.tepco.co.jp/en/news/110311/index-e.html
In 1F3, TEPCO is trying to pump the highly contaminated water to its steam condenser well, which can store as much as 2000 tons of water.
II. Installation of new pressure measurement instrument
Recognizing the insufficient reliability of 1F1 pressure gauges, a set of new pressure gauge is being installed. I believe this is a prudent operation, since most of the pressure gauges are showing strange readings, including differential pressure level gauges as well as the different pressure flow meters. I am suspecting an occurrence of the “internal hydrogen explosion”, since there are 8 cases in TEPCO that gauges are broken by sudden high pressure and temperature during normal operation. In the cause of the accident, since there were no water circulation, there could have been more chances for hydrogen accumulation and separation from water, leading to the hydrogen explosion. In all of the reactor pressure vessels, there were events when the pressure suddenly drops followed with strange readings after. These incidents have been known inside TEPCO and reported in Japanese in the following addresses:
These investigations were reported in the light of the Hamaoka Unit 1 hydrogen explosion/pipe rupture accident, which occurred at a part of ECCS piping, as introduced in Earthquake (70). I am suspecting that similar events have occurred one after another during March 11-16, resulting in the“spontaneous venting.”
Also in 1F1 turbine hall, the water level of the highly contaminated water slightly decreased, probably leaking into other area of the turbine hall. Currently no sign of leakage into the underground water has been suspected.
III. Prevention of leakage of highly contaminated water into the sea
Today TEPCO reported to NISA that they have investigated whether there can be another contaminated water leakages such as occurred from 1F2 in April and 1F3 in May. According to their study, the most vulnerable leakage passes are through “trenches” which lead cable to the pumps and screen facilities from the basement of turbine halls. There are total of five of them as well as 39 “pits.” They are currently pouring concrete in the pits one by one. They are also trying to fill cracks in the concrete walls facing the sea. These operations should be completed by the end of this month.
IV. Recapping on water supply lines recovered for all of 1F1-4 spent fuel pools
After start operation of the air cooled decay heat removal system in 1F2, the temperature dropped down to 39 degrees, 10 degreeC lower in a day, achieving the one month goal of cooling down in just two days. Similar operations are being planned in other plants and should be ready by early next month.
Well, let me stop here today.
Date: Wed, 01 Jun 2011 22:21:19 +0900
Subject: Earthquake (82)
From: Genn Saji
I. Recapping on the 1F4 water radiolysis studies
Being motivated by the Professor Yousuke Katsumura’s rapid experimental test, I also tried to provide a trial detailed radiation chemistry calculation as attached. Through my study, I could extract the following accident scenario.
(i) Due to the “station blackout”, the circulation of the SFP water was terminated.
(ii) This resulted in a rapid removal of oxidative radicals through water radiolysis, resulting in termination of
the reverse reaction for reducing hydrogen generation.
(iii) This resulted in a substantial increase in the radiolytic hydrogen generation rate.
(iv) With the rise of the temperature of SFP water, th DH is released to the Fuel Exchange Room with steam bubbles.
(v) The steam was condensed in the wall of the room, separating the hydrogen gas.
(vi) When the hydrogen concentration reached to the flammability limit, the hydrogen explosion occurred.
This mechanism should be different from that of 1F1-3, where much more amount of hydrogen gas was released
through venting, both manually and spontaneously.
II. Recapping on water supply lines recovered for all of 1F1-4 spent fuel pools
After start operation of the air cooled decay heat removal system in 1F2, the temperature dropped down to 49 degrees, 20 degreeC lower in a day, indicating that the system is working as intended. This is going to help greatly, since the successful operation should prevent diverting recovery efforts to more urgently needed areas.
III. More effective water injection through feed water lines
TEPCO changed the water injection line now through the feed water lines from the previous fire fighting line routes, resulting in some decrease in the necessary water injection rate than before.
unit thru feed water line thru fire fighting line temperature at lower portion of RPV (June 1)
1F1 5 m3/h 6 m/h 108.4 degreesC
1F2 4.9 7 110.2
1F3 11.5 6 + 12 (feed water l.) 136.4
I believe this is an indication that a significant portion of the injected water has been leaking before reaching to the RPV.
IV. Zeolite sea water decontamination facility installed near the sea water intake port for 1F2/3
Please visit http://www.tepco.co.jp/en/news/110311/index-e.html to see
Circulating Seawater Purification Equipment at the Fukushima Daiichi Nuclear Power Station (pictured on June 1, 2011).
The unit is expected to start operation tomorrow, after replacing the faulty cable. It has a capacity of 30 tons per hour.
V. Total cost of decommissioning Fukushima Daiichi
The Japan Economic Research Center, a private institution, reported to Atomic Energy Commission that the cost of decommissioning of the Fukushima Daiichi as well as paying compensation to the evacuees, may reach 70 to 250 billion dollars in the coming 10 years. The cost estimation was made by referring to the case of the Chernobyl accident.
Well, let me stop here today.
(Previous e-mail sent at 0:0? AM on June 1 as Earthquake (81))
I. Recapping on Two TEPCO operators found received excessive internal radiation exposure
TEPCO investigated why the two operators received nearly 10 times more of internal doses compared with other operators. It began to reveal some clues.
(1) They neglected to wear masks when they were struggling at the control room on March 11.
It appears that masks can reduce the aerosol inhalation by a DF of 10.
(2) They only took the iodine pill on March 13, distributed by TEPCO.
If that is the case, it is too late. The iodine pill is to saturate thyroid with stable iodine. It is not so effective unless
taken at the very early stage of iodine exposure.
TEPCO continues to investigate into this issue.
II. Recapping on water supply lines recovered for all of 1F1-4 spent fuel pools
Today, TEPCO has started operation of an air cooling system in 1F2 spent fuel pool. It is hoped to bring the temperature down to 40 degreeC from the current temperature of 70 in a month or so. With the reactor building is covering the damaged spent fuel pool, the hot water releasing a lot of moisture inside of the reactor building, resulting in nearly 100% in relative humidity. Similar air coolers are being prepared to be ready early next month in 1F1 and 3, followed with another one in 1F4 in July.
III. Recapping on the “scheduled (and organized) evacuation” status
At the time limit of one month came today, 1800 people (18% of population) have not been evacuated yet. Especially at Iidate-mura, 1427 people (23%) of the total population of 6177 have evacuated. Those families with small children or living in the highly contaminated zones are mostly evacuated. However, those who have not found a good way to dispose of their cattle or those small business factories unable to do business at another relocated site are still remaining there. However, the government has relaxed their guidelines for these factories allowing them to stay there to keep their business going. In those places, the first thing the workers do in the morning is to put down the dosimetory readings at the entrance of the factories, where some measures for dose reduction, such as closing the openings to a minimum and taping the gaps around the windows are provided. Many of the ranch owners have to close their business, mainly because they are unable to provide pastures in their farm lands. They are all crying since it took years for them to build up their ranches and raised their cattle. They are all feeling that they lost their reason for living. The monetary compensation cannot recover their salt of life.
IV. Recapping on the continued threat of leakage of rain water
Due to the heavy tropical low pressure, the heavy rainfall into the damaged reactor buildings increased the volume of the highly contaminated water in the buildings. For example, the water level increased 38 cm a day in 1F1, 6 cm in the basement of 1F3 turbine halls. The most critical situations are in the water accumulated in the 1F2 and 1F3 trenches, now rose to 39 cm below the ground level in 1F2 and 29 cm in 1F3. Since the new water purification system is not anticipated to be ready until July, TEPCO is looking for some other storage facilities. With its very high activation, it cannot be stored in the open tank yard, now being constructed on the site.
Well, let me stop here.
((Previous e-mail sent at 10:21 PM on May ?0 as Earthquake (80))
I. Recapping on 1F4 spent fuel pool situation
Through this accident, the mother nature left us many mysterious issues, indicating that our understanding of the nature is much limited. One of the mysteries is the hydrogen explosion in the 1F4 pool, where all the fuel assemblies were moved into the spent fuel pool at the time of the accident. Many distinguished scientists and engineers insisted that the hydrogen must have generated through the zirconium steam reaction at a high temperature.
In order to find a clue to this issue, Professor Yousuke Katsumura and his colleagues performed an urgent radiolysis test using hot water. He was kind enough to provide me his draft paper, unpublished. With his permission, I made an urgent condensed translation as attached. They tried to confirm their hypothesis that the hydrogen produced through radiolysis of the boiling water is released with steam and condensed in the room by separating the hydrogen gas.
I am also suspecting that the hydrogen is produced through water radiolysis, however in my opinion, the dissolved hydrogen containing up to the solubility limit at the operational temperature in the pool water was released to the room atmosphere by heating up near to the boiling temperature. It is more of well known Henry’s law.
Also, one of my audience informed me the picture of 1F4 pool released on March 31with annotated explanation by
<http://www.fairewinds.com/content/fukushima-unit-4-fuel-racks> I could not identify the fuel rack at that time and did not introduce this photo. After this more clear picture was taken on April 29 as introduced in Earthquake (50). ( 188.8.131.52 The spent fuel pool of Unit 4, Fukushima Daiichi Nuclear Power Station (video on April 28th, 2011):
The fuel rack appears to be the one with a size of approximately 1.2x1.7 meters with 4.2 meter tall for storage of 60 spent fuels.
Today TEPCO also released a set of photos taken inside of the 1F4 reactor building showing a very clean situation inside. It is very different from what we have been seeing in 1F1-3, with full of debris and often with water leakages.
( http://www.tepco.co.jp/en/news/110311/index-e.html#header “Inside the Reactor Building, Unit 4, Fukushima Daiichi Nuclear Power Station)”. It appears that the mechanism of hydrogen explosions in 1F4 should be different from those in 1F1-3.
II. Two TEPCO operators were found received excessive internal radiation exposure
A whole body exposure measurement performed at JAEA to account for internal exposure identified two control room operators who have accumulated the thyroid exposure from I-131 at 9760 Bq and 7690. Combined with the external radiation, the converted total doses may exceed the 250 mSv limit, the limit specified for recovery activities for nuclear accidents.
III. Continued threat of leakage of rain water
With a heavy rainfall induced by the typhoon, the volume of the highly contaminated waters are increasing rapidly, now threatening for overflow from the trenches. In the 1F1/1F3 turbine hall basements, the level increased by 19.8/4.2 cm a day, respectively. At the trench of 1F2, the water level has increased by 6.2 cm. TEPCO quickly put sandbags to be prepared for possible overflow. Fortunately, the typhoon now is heading toward the NE direction and has already diminished into a tropical depression. However a heavy rain is still predicted in the Fukushima region tonight.
Well, let me stop here tonight.
Date: Mon, 30 May 2011 00:03:21 +0900
Subject: Earthquake (79)
From: Genn Saji
I. Water supply lines recovered for all of 1F1-4 spent fuel pools
The water supply to the spent fuel pools was provided through a piping from the Condensate tank before the accident. Since this function was destroyed by the tsunami, the pool water has been injected by using concrete pumps. TEPCO announced yesterday that these feed water routs are now recovered and can supply water by using the normal Fuel Pool Cooling and Water Purification System, although the cooling function is still not available due to the メloss of ultimate heat sinkモ. External air cooling system will be installed soon to recover this cooling capabilities.
II. Near emergency in the loss of the 1F5 sea water pump
On Saturday night, the temporary sea water pump was found not working. The temperatures both at the reactor vessel as well as at the spent fuel pool were started to increase as high as 93.7 degreeC in the reactor vessel last night. Fortunately, TEPCO was able to replace the pump by the noon today and another emergency was avoided. Since the temporary pumps are vulnerable without sufficient monitoring from the control room, the trouble seems to have been unidentified. It is necessary to provide a temporary I&C system so that its function can be monitored from the control room. TEPCO staffs seem to be taking that this issue as a minor trouble, however, the sea water pump is now in a safety grade for decay heat removal, even it is temporary.
III. Cs-137 found in the sediments of the sea water
MEXT collected 12 samples of sedimentation from bottom of the sea of 300 km square during May 9 to 14. Their analyses indicated as much as 110 Bq/kg of Cs-137 from a sample takes 30 km off shore, 45 meters deep, 50 Bq/kg off Mito, 45 meter below the tidal surface. Specialists are speculating that the contamination was first picked up by plankton and deposited at the sea bottom. No data are shown yet about the strontium contamination, however, the real threat is in Sr-89 and 90 in the marine food chain, I believe.
IV. Recapping on more detailed environmental monitoring data released today
For last two days, I have been spending a significant amount of my time to investigate the environmental monitoring data released on May 27 from TEPCO. Currently I could only plot the results in a form of Monitoring-Events graph as attached. On this issue, I have introduced several time in the past, but this in the newest one. My general observations are:
(1) With more detailed environmental monitoring data released from TEPCO, including the raw data of every 2 minutes, the overall picture of large release events became visible more clearly, although they are limited to only a few locations around the damaged plants. Depending on the wind direction, some of the important events may have been overlooked.
(2) Nevertheless, the reported 1F1 events and the environmental monitoring records are now relatively well correlated. However, it appears that there was a subsequent large release event from 1F1 after the hydrogen explosion. I have been suspecting this through my assessment of the land contamination maps released from DOE/NNEA ( http://energy.gov/news/10194.htm ). For more detailed explanation, please refer to the attachment.
(3) Further destruction of the plants seem to have occurred spontaneously even after the hydrogen explosions, continue releasing large amounts of radioactive effluents. The mechanism of these releases are not known yet.
(4) The large releases occurred between March 12 to 16. Previously, I though it was limited uppp to March 15. However, TEPCOユs new environmental monitoring data are showing another large release event occurred on March 16.
I do not think these releases are due to core melt though, since after releasing the contaminated steam, the events terminate by themselves spontaneously. I will study these results more in detail by referring to TEPCO released メPlant Dataモ to identify possible correlation of the operator actions with the environmental monitoring data.
Through my quick study, I noticed that TEPCO seems to be not releasing the raw data for March 15 and 16. Since there are several uncharacterized large release events identified as attached. The raw data are highly requested, if available. The environmental monitoring data, although they were taken by monitoring cars and survey meters, the data are one of the few robust data available for this accident due to the station blackout which induced blackout of the control panels.
Well, let me stop here today on Sunday.
(Previous e-mail sent at 0:00 AM on May 29 as Earthquake (78))
I. Improvement of medical assistance to radiation workers at Fukushima Daiichi
On May 14, a worker passed away, at the age of 60, by a cardiac infarction during the time when on site industrial health care doctor was absent. Unfortunately it took two hours to send the patient to the hospital by an ambulance. The doctor was staying at the site every other day, only during day time. In the light of this, the Ministry of Health, Labor and Welfare made an arrangement to have a industrial or roentgenology doctor to stay 24 hours at the site in rotation. The doctors are all worried about deterioration of the working environment in the coming summer while wearing air-tight radiation protection suits.
II. Recap on the MEXTユs plan to construct a detailed land contamination map.A question was raised from one of the audience of this daily updates,
by saying メHow did MEXT pick the top 5 cm of soil? Why not the top 1 cm? What percentage of fallout is trapped by the first cm, the second? Aren't people exposed to mostly the fines in the surface layer? Does the bottom 4 cm just dilute the top 1 cm?モ The attached one page memo should explain to this question.
In the projected soil sampling in Fukushima by academia for construction of a detailed land contamination map, they plan to collect soil samples up to 5 cm from the surface and the total activity of each nuclear species will be shown per sample. By knowing the area of the sampler used, the results will be converted to Bq/m2, the unit used at the time of Chernobyl accident.
III. More detailed environmental monitoring data released today
Currently I am checking the new data. It is nice to find more data on March 11.
Well, let me stop here today!
(Previous e-mail sent at 9:27 PM on May 27 as Earthquake (77))
I. Recapping on remediation of school grounds
On this issue, I have recapped in Earthquake (51), (58) and (71) in the past. Today I learned from media reports that the MEXT showed a new guideline for ALARA to 1 mSv a year for school exposure. The Government will support 98% of necessary costs for remediation when the surface contamination level exceed 1 microSv/hr at school. The government is going to re-measure the contamination level and identify school ground for remediation, working closely with the Fukushima municipal government. This issue is likely to be resolved in an appropriate direction, I believe. However, I am concerned that general public do not seem to understand there is no threshold between a safe and non-safe limit in the current LNT hypothesis. This seems to be making people suspicious that the government is hiding something grave.
II, Distribution of dosimeters for every school children.
In Kawamata-cho, Fukushima, the municipal government decided to distribute a personal dosimeter to each school children of day nurseries, Kindergarten and grade schools, in the total of 1500 school children. These will be collected once a month and checked by a private monitoring company. The dosimeters were supplied by Kinki University who offered to measure doses of the school grounds there. I can foresee this will spread more widely in the highly contaminated areas in Fukushima.
III. Health monitoring in Fukushima
MEXT also distributed dosimeter to all of the 1200 plus schools in Fukushima. The schools include day nurseries, Kindergarten, grade schools and high schools. The ministry is requesting the principals to report the readings once a month. The results are free for each school to release locally.
In addition, Fukushima Prefecture government decided to screen all of their residents of 202 million people to estimate radiation exposure since March 11 asking them to respond to a questionnaire. The total accumulated doses are estimated to select a cohort whose radiation health effects will be monitored for several tens of years. For high dose group, continuous blood and urine tests, as well as whole body monitoring will be performed. The procedure is similar to what was done to select the LSS (Life Span Study) cohort for Hiroshima-Nagasaki atomic bombing survivors.
IV. Recapping on a leakage from the contaminated water storage facility
I introduced this story yesterday. TEPCO converted the basement of Miscellaneous Solid Waste Compacting Facility for temporary storage of the highly contaminated water for 1F3, however, the water level inside started to get lower even without pumping. A worker found that the underground corridor is being flooded with water. The corridor connects this facility to the Process Room in the Centralized Waste Treatment Facility. The contact dose rate was 70 mSv/h, not very high compared with the dose rate of the 1F3 basement water of the turbine hall. This dose rate appears to be that of the trench of 1F3.
The increase of the volume of the contaminated water coming from the underground water is becoming an increasingly troublesome issue, since Fukushima will soon go into a rainy season. As a matter of fact, here in Yokohama, where I live, entered into the rainy season today. On top of that a large typhoon is heading toward Japan threatening Japan. The underground water level can substantially increase during the rainy season.
V. Cost of processing the highly contaminated water
TEPCO explained today that a cost of the contaminated water processing is estimated to be approximately $2.60 per litter.
VI. More detailed environmental monitoring data will be released soon
Today TEPCO reported that there are still un-incorporated data from the environmental monitoring station waiting to be released. Upon hearing this news, Mr. Edano, the Chief Secretary of State, was furious, after the fuzzy issue as to the initiation of the seawater injection. I can guess what the data is all about. Due to the station blackout, all of the environment monitoring posts went dead. TEPCO quickly set up a portable dosimeter in place of the the monitoring stations, as well as put a monitoring car dispatched from Tohoku Electric Power Company. The software system of this monitoring car seems to be different from the one used by TEPCO and could not have been able to incorporate these data yet. I can tell this since I have already used a part of this data and introduced in Earthquake (62). Certainly, I have been waiting this set of data be released soon, because there are several release events which are not well correlated with the currently available monitoring data. I do not think TEPCO is intentionally hiding the data or anything. Just due to a possible technical difficulty.
Well, let me stop here today!
Date: Thu, 26 May 2011 22:43:21 +0900
Subject: Earthquake (76)
From: Genn Saji
I. Initiation of the sea water injection to 1F1
For last several days, at the current Diet session, there has been a big political argument whether the Prime Minister ordered to suspend the sea water injection, which was started at 7:04 PM of March 12, due to his concern about re-criticality through the sea water injection, reported to be advised from the Chairman of the Nuclear Safety Commission. Each people involved changed their explanations each time and induced a lot of confusion among the Japanese people. So far, TEPCO was reporting that the sea water injection was suspended at 7:25 until 8:20 PM for 55 minutes. TEPCO made a correction today that the sea water injection has never been suspended, due to a judgment of the Fukushima Daiichi Director, Mr. Yosida. Since no record nor process computer records are not available in support of this operation, he public entertained doubts about the Government as well as TEPCO.
In addition, those people who are still evacuated because of this accident were dismayed at these political scenes, by saying this is not the time to argue who said what, rather wanted to see the politician discussing how to stop that nuclear accident.
II. MEXT decided to construct a detailed land contamination map.
The Ministry of Education, Culture, Sports, Science and Technology (MEXT) decided to construct a detailed soil contamination map of the entire district of Fukushima. The soil samplings will be made every 4 km2 within 80 km, every 100 km2 beyond, from 2200 locations. Each sample will take 5 cm deep soil, by mobilizing 25 universities and research institutions.
With already detailed land contamination map released by DOE/NNEA, I do not see why they can make a better planning of resources such as by distributing more measuring points at the heavily contaminated regions located at the NW direction of the Fukushima Daiichi. This region has a width of 20 km and a length of 50 km, which should call for more detailed measurements. For the land of habitation in the Iidate-mura, for example, a detailed soil contamination map is highly waited, I believe. At the same time, I worry about possible exposure of students by entering this region for sampling, since the dose rate is high as 100 microSv/hr. In addition, most of this highly contaminated region is located across the Abukuma mountain chains and a mountain climbing is going to be necessary, with much difficulties in collecting soil samples. It is a kind of radiation work. Considering these difficulties, I do not think the MEXTユs plan is feasible, I am afraid.
III. A leakage from the contaminated water storage facility
TEPCO converted the basement of Miscellaneous Solid Waste Compacting Facility for temporary storage of the highly contaminated water, after waterproofing, with a capacity of 4000 tons. After pumping 3700 tons from 1F3, the water level started to decrease by 4.8 cm in 20 hours. The leaked water is likely went into another areas of this facility. Currently TEPCO intensified monitoring.
Well, let me stop here today!
(Previous e-mail sent at 10:55 PM on May 25 as Earthquake (75))
I. TEPCO uploaded the accident scenario of 1F1 and results of core melt analysis for 1F2 and 1F3
As I introduced in earthquake (74), TEPCO made the following Press Release (May 24,2011),
Submission of a report on the operation of the plant based on the plant data etc. of Fukushima Daiichi Nuclear Power Station at the time of the earthquake to NISA.
Please visit the website to look into their results.
Attached please find an update of my メback of an envelopeモ calculation performed to include the メfeed and bleedモ function for 1F2 and 1F3, which releases the reactor vessel pressure through automatic release and safety valves. The メreleaseモ function requires a battery power, however, the メsafetyモ function actuates even in an event of the station blackout. It will take about a day for the reactor level to be down to the bottom of the fuels in the 1F2 case and about half a day for 1F3 case. The case for 1F1 has been shown previously in Earthquake (70). This update is attached just for completeness and I do not intend to challenge the results by TEPCO. I think this kind of issue should be assessed in the future more carefully when everything settle down. I do not believe the we have to make a hasty conclusion that a gross core melt has occurred in 1F1 to 1F3.
II. Glowing evidences for pipe failure accidents during the first few days.
TEPCO disclosed that there could have been a pipe failure accident soon after the earthquake, resulting in a leakage of the reactor water. Their analyses show that a 7 to 10 cm diameter equivalent holes in 1F1 and 1F2. At the night of March 11, a very high radiation was detected in the 1F1 Reactor Building, and operators suspected a pipe failure. For 1F2, a postulated failure as large as 10 cm diameter hole assumed to have occurred at 21 hours after the seismic trip yields a good agreement, according to TEPCO. For 1F3, the High Pressure Coolant Injection System was started around 12:30, however, both the reactor pressure vessel and containment vessel pressure suddenly dropped. By performing an analysis by assuming a pipe break in HPCI, the results of the pressure transient agrees well.
I also found that TEPCO has experienced eight hydrogen explosion damage cases to the instrumentation systems in normal operation ( http://www.tepco.co.jp/cc/press/betu03_j/images/030821b.pdf and http://www.tepco.co.jp/cc/press/betu03_j/images/030821d.pdf, in Japanese ) between 1994 and 2001. These events have a common feature that the damaged portion appeared to have exposed to a high temperature and pressure. In pressure transducer cases, a sudden pressure peak is detected, followed with no indication or abnormal indication. Post accident examination revealed that the sensor was broken by overpressure and high temperature.
I am increasingly confident that an メinternal hydrogen explosionsモ have occurred in all of these cases. I introduced this possibility in Earthquake (69) by attaching an one page summary of the Hamaoka Unit 1 pipe rupture accident.
III. Additional storage capacity of the highly contaminated water
TEPCO disclosed that the Centralized Waste Processing Facility can accommodate additional 5000 m3 of the highly contaminated water on top of the almost full situation so far disclosed. I remember that they wanted to make a further check to use it in full.
IV. A memo for lessons learned from the tsunami-induced nuclear disaster (continued)
For memory sake, let me add lessons learned.
(56) メInternal hydrogen explosionモ and instrumentation
In following plant data released from TEPCO during this accident, very often the indication of pressure and level gauges have been showing unreasonable reading. In view of this, TEPCO had an instrumentation engineer to go inside to the reactor containment vessel to re-calibrate the level gauges. Through this reading, TEPCO changed their view that the entire 1F1 reactor core has now lost its submerged status, resulting in the core melt scenario.
However, the current plant data indicate that the fuels are reasonably cooled inside of the reactor pressure vessel. The image of molten core at the bottom of the cold reactor vessel are not compatible for me. While looking for evidence of a possible occurrence of the メinternal hydrogen explosionモ as occurred in the pipe rupture accident at the Hamaoka Unit 1, induced by a hydrogen explosion, I noticed that there are several precedents experienced between 1996 to 2001inside TEPCO, who has been charged by an anonymous accusation. TEPCO made a response in Japanese in the following document. http://www.tepco.co.jp/cc/press/betu03_j/images/030821b.pdf
Since the troubles resulted in minuscule damages to small diameter instrumentation piping only, with no environmental effects, they were fixed internally. TEPCO also had been performing R&D studies before the accusation. According to the report, it tends to occur in horizontal instrumentation piping, damaging the pressure transducers. Sometimes a pressure surge is observed, followed with sudden loss of the reading.
Although the radioactive release might have been disregarded, the loss of instrumentation function can be of a safety concern. As a matter of fact, unreliable indications of level and pressure gauges confused accident management. In particular, many pressure transducers are connected to horizontal instrumentation pipes, which should have been vulnerable for hydrogen accumulation.
(Previous e-mail sent at 1:12 AM on May 25 as Earthquake (74))
I. Activity data of the highly contaminated water at turbine halls
On May 22, TEPCO disclosed a set of activity data taken from the basements of 1F1-4 turbine halls. These data
have been sampled on March 24 and 27. The early information was first released on March 25, however some errors had slipped in and TEPCO was admonished by NISA to improve quality of data. After that, they released only the
data of I-131, Cs-134 and Cs-137, to be followed with more detailed data, confirmed by the third party, after going through a reviewing process by a group of specialists. After going through these procedures, TEPCO released detailed data two days ago.
These are very precious data, I believe, since they are a few of the robust data hiding メfoot printsモ of the accident procession. For estimation of the extent of core damages, for example, these data should become a starting point. Recognizing the importance of the data well, I compiled the data as attached. The original is posted in the following website. http://www.tepco.co.jp/nu/fukushima-np/images/handouts_110522_04-j.pdf (in Japanese)
I made a scoping study by using this data to estimate the fuel damage fractions as attached. It is very strange to find somewhat different footprint left by 1F2 with an order of magnitude larger sampling data compared with both 1F1 and 3. For more detail, please read the remarks in the attachment.
II. The メmelt-throughモ analyses released for 1F2 and 1F3.
Following the melt-through scenario as most recently explained in Earthquake (70), TEPCO released their assessment of the severe accident assessment of 1F2 and 1F3, mostly through extending the assessment of 1F1. For 1F2, around 1:00 PM on March 14, three days after the earthquake, the total loss of the cooling capability occurred, followed with a start of core melt at around 8:00 PM. By this time, most of the fuel meted down to the bottom of the reactor vessel. A similar results are also provided for 1F3. I have not performed a follow on メback of an envelopeモ calculation yet, but form their illustration, they ignored the effect of メbleedモ cooling. Since the decay heat is further down as compared with the 1F1case, I believe we should have much longer time allowance that what is being predicted by TEPCOユs pessimistic scenario.
One of the new points of the TEPCOユs analysis is that they provided hydrogen generation rate, through zirconium water reaction. According to their estimation, 800 kg for 1F1, 300 kg for 1F2 and 600 kg for 1F3, In another interview, they explained that a portion of the hydrogen flowed through a common ventilation duct to 1F4, hydrogen gas discharged through venting, inducing the hydrogen explosion there. I forgot to introduce this scenario. Some of the difficulties in this is that the ventilation ducts are severely damaged through a series of preceeding hydrogen explosion nor ventilation fans to the common stack were working due to the station blackout.
Anyway, I do not think this kind of argument is helpful in finding an urgent way to mitigate the consequence of the accident. For me, the most important issues are (1) find an effective way of the damaged core cooling, (2) without substantial increase in generating the highly contaminated water. Since a large fraction of injected water seems to be leaking before reaching to the reactor vessel, finding a better cooling water passage is urgently needed. TEPCO appears to be injecting a few times more water than necessary to remove the decay heat according to heat balance studies performed by many people. The water injection through the ECCS may not be effective, in referring to the Hamaoka Unit 1 hydrogen explosion experience. A better route should be through the feed water line, which is located at a lower level.
III. Root cause of the メloss of off-site powerモ
The Fukushima Daiichi and Daini are hooked up with six transmission routes to the TEPCO grid. TEPCO reported to NISA to answer to the question of why external power source was all lost by the earthquake. Four transmission routes went out, due to shorts induced by the earthquake. The remaining two went down due to damages at switchyard. Due to these troubles, the circuit breakers tripped. One of their nearby transmission tower tumbled down due to a land slide from a hill, although the tower itself was designed against earthquakes. The earthquake again demonstrated the common cause nature. TEPCO has been boasting that loss of off-site power is not likely at Fukushima thanks to the sufficient redundancy.
IV, TEPCO continues to find the operation of the Isolation Cooling System
According to their investigation of the plant data, the turbine driven Isolation Cooling System automatically started at 14:52 but manually stopped at 15:03, 11 minutes after. At 18:18 and again at 19:30, operators attempted to start up again, however, the actual operation has not been confirmed yet. If so, it is strange since the battery power was thought to be still available until 10 PM. They continue to investigate this issue.
V, International investigations
Stating today, on May 24th, a team of IAEA dispatched an expert fact-finding mission to Japan to make a preliminary assessment of nuclear safety issues at the Fukushima Daiichi nuclear power plant following the March 11th earthquake and Tsunami. The Japanese government assured that any necessary data will be open to them. Mr. Weightman from England will present the mission's report at the Ministerial Conference on Nuclear Safety organized by the IAEA in Vienna from 20 to 24 June 2011.
The UNCEAR also decided to investigate the radiological consequences of the Fukushima accident. They plan to spend two years for their investigation, to complete their preliminary report in May, 2012, Professor Wolfgang Weiss from Germany spoke at an press interview.
Well, let me stop here!
Date: Mon, 23 May 2011 21:44:58 +0900
Subject: Earthquake (73)
From: Genn Saji
I began to notice that, although the Fukushima Daiichi plants are not completely under control, the reports from TEPCO as well as the Government are becoming less frequent, since the ‘time constants’ of the accident became much longer. I plant to follow the daily progress best I can, however, if you started to feel annoying, please drop me a line so that I can stop sending you my daily updates. I can now spend more time on my assessment of the accident. Currently, my high priority is to make further progress in confirming the root cause of the 1F4 hydrogen explosion from a radiation chemistry point of view.
I. Gamma camera view of 1F1
I have been waiting for the TEPCO to upload the gamma camera view in English. Here it is.
When you first crick the optical view image, followed with another crick to see the gamma camera image, you will find that the very high dose region is from a piping, located near the ventilation duct. Although the gamma camera does not tell the actual dose rates, it should be a very powerful tool to identify hot spots. For general explanation of gamma camera, see
II. No significant earthquake damage in Fukushima Daiichi, but it was tsunami that devastated the plants.
Following the release of the plant data on May 16, TEPCO confirmed that the plants responded to the seismic trip signal as designed, all the reactors went into sub-critical states, followed with the planned decay heat removal operation sequence without any serious problem. After the arrival of the tsunami, Fukushima Daiichi went into a “station blackout” combined with a “loss of ultimate heat sink” situation. After the tsunami, the available plant data are much limited, only the data obtained by dispatching auto batteries to the control room. Therefore, TEPCO collected information by interviewing the operators through fact-finding on the spot. This indicates also indicate that the plants went into the “(feed) and bleed” operation as designed, by releasing the reactor water into the suppression pool by “bleeding” from the automatic release and safety valves, while sacrificing the water inventory. The TEPCO continues the fact- finding of the operation of the turbine-driven Isolation Cooling System (a part of ECCS) of 1F1. The ECCS was said to be manually terminated before arrival of the tsunami. On this issue, I made a “back of an envelope” calculation in Earthquake (71) to assess the effect of early termination. My study indicated that the recovery/maintaining the reactor water level by subsequent recovery of the ECCS should have been more critical. Unfortunately, no clear data are available to confirm this point yet.
III. Continued critical situation in the storage of the highly contaminated water
It was disclosed today that the Centralized Waste Processing Facility, which is being used for the water storage after making the building water proof, has been approaching to a full level in a matter of 4 days. TEPCO plan to keep the water at the basement of turbine halls, while intensifying inspection for possible leakage. They have to wait for the availability of temporary water purification facility in mid June. So far, 8700 tons of water was pumped from 1F2, and 2700 tons from 1F3.
The aerosol monitoring sample of the 1F2 revealed 0.024 Bq/cm3. It is reported that the sampling was questionable, being 1/10 ミ 1/100 of the value obtained by the “PackBot” on April 18. TEPCO plans to re-sample the air again. I stopped to convert this to a dose rate.
Well, let me stop here today!
(Previous e-mail sent at 8:36 PM on May 22 as Earthquake (72))
For last few weeks, I was so busy in doing my assessment of the Fukushima Daiichi accident and I did not have a time to introduce a hart warming story. That is, in spite of the tsunami death toll over 15,000, there were not a single death from the 315 day nurseries caring babies and pre-school children in the earthquake stricken districts. At the time of the earthquake, infants at these nurseries were at the time of afternoon nap. The nurses quickly woke them up, hump babies up to the nearby heights, pushing toddlers in big baby carriers (called evacuation carriers, commonly used in these facilities for taking kids to nearby parks), followed by small children on foot. Many of the nurses made best judges while observing the magnitude of the tsunami, moved up and up trying to escape from the tsunami. These facilities have been exercising drills for tsunami, earthquake, and fire once a month. For example, at Noda-mura day nursery in Iwate Prefecture, the tsunami washed away its building, leaving behind only the front gate. Twenty eight villagers were dead among the population of 4700, 450 houses were destroyed. In the drill, they were supposed to evacuate to a “hill top house”, 500 meters away, however, the chief nurse Ms. Yuko Hironai (53) judged it may not be safe enough this time and quickly decided to run another 500 meters to “Genpei Hill”. When glancing back they observed many autos were being washed away from the country road below. Their 90 babies and kids, with 14 staffs all survived. There are many miracle stories like this. The nurses are really professionals, knowing well their vulnerabilities with babies and kids.
I. Recapping on remediation of the school ground
(Earthquake (51)) Professor Kosako appeared at a press interview and strongly criticized the government’s decision, especially related with allowing the accumulated dose to 20 mS/y for children, from the previous 1 mSv. He also criticized sharply the Prime Minister’s accident management policy by saying that the decisions were made in a haphazard way. In addition, he has been insisting on dissemination of the results of atmospheric dispersion code, SPEEDI, during the early phase of the accident.
(Earthquake (58)) Following the surface soil removal method performed by Koriyama-shi to reduce the dose rate of some of the school grounds, Fukushima-shi tested a method to put the contaminated surface soil at the bottom of the soil whose surface was temporary put aside. By digging up to 50 cm, the dose rate decreased by a factor if ten. Before this treatment, the dose rate at the surface was 2.3 - 2.1microSv/h. After the treatment, the dose rate went down to 0.2 microSv/h. Another test showed that this method can be equally effective, when the depth is around 20 cm.
By taking these messages very seriously, parents of school children of the schools with contaminated school grounds applied pressure to the local government to reduce the dose rate as low as reasonably achievable (ALALA). Currently as many as 217 school grounds are being in remediation or scheduled to be decontaminated. The method is now converging to remove the 3-5 cm of surface soil and put it into a deep pit and cover the contaminated soil with about 1 meter thick clean soil. The estimated cost is in an order of 7.5 million dollars. Although the local governments are requesting to MEXT for support this operation, the government is not prepared for such a budget, since their official position is 20 mSv/y. The government has not decided what to do with the expenditures.
Even after the remediation, or with grounds less contaminated, most of the schools are refraining form using the school grounds, replacing them with gyms, having their sports day indoor.
Well, this kind of news made me feel happy, since there are a lot of unknowns in the effect of low level radiation to youngsters. Even among the Hiroshima-Nagasaki LSS cohort, the real radiation risk may not become clear until most of them passed away, another a few tens of years. However, the LSS cohort tends to live longer, perhaps because they pay more attention to their health and they are under better health examinations, although their quality of life is a different issue. A kind of selection effect. However, they also tend to suffer from non-cancer malignant diseases more than unexposed comparison group. Not only that, the LSS cohort have received significant doses just once in their life. The effects of the continued irradiation of 20 mSv for a long time is not completely known although ICRP’s principle is to limit the life time accumulated dose to less than 1 Sv for human being.
Not also that the amelioration of the school grounds are limited to only the least contaminated areas, Zone I as introduced in Earthquake (61). These schools are distributed in the “Naka-dori” district of Fukushima Prefecture, the wide and flat valley districts between the Abukuma Mountain Chains to the east and the Ohu mountain Chains to the west, with the contamination area of 956 km2 in the following grouping
Zone Cs-total (Bq/m2) area (km2)
V 6E+06 - 3E+07 151
IV 3E+06 - 6E+06 116
III 1E+06 - 3E+06 483
II 6E+05 - 1E+06 379
I 3E+05 - 6E+05 965
should become necessary.
It is interesting to see a decontamination experiment being performed by a volunteer group for a farm house. According to their experience, cleaning the roofs and gutters seems to be effective in reducing the dose rates.
Also, some people are interested in using biotechnology for remediation of the contaminated farm lands. I do not know how the soil bacteria can reduce the dose level. It appears to strip cesium out of the soil taking into the cells of bacteria, and can be mixed more evenly by cultivation. http://tidt.jp/pdf/110513/fukugo-en.pdf
Well, let me stop here today, Sunday, to be refreshed for better tomorrow!
(Previous e-mail sent at9:18 PM on May 21 as Earthquake (71) with corrections to (Corrected) H2andO2 Accumulation.pdf.)
In trying to confirm my H2 and O2 calculation by solving the detailed chemical thermodynamics equations, I found an embarrassing error in converting the g-values expressed in molecules per 100eV into SI unit. Attached please find a corrected version. The results are not that hazardous as I contemplated but still not completely free from a concern. If the suspected “internal hydrogen explosion” had actually taken place, the important question is a separation of hydrogen gas from the reactor coolant and accumulation of the gas in the pipe line located at the upper portion of the reactor vessel.
I. A memo for lessons learned from the tsunami-induced nuclear disaster (continued)
For memory sake, let me add lessons learned.
(54) Radiation chemical studies in the accidental situation
From the day of Manhattan Project, the field of radiation chemistry has been studied deeply through 1960th. This provided scientific foundation of this field necessary to address water radiolysis behavior during normal operational conditions, although there are many unresolved issues for engineering application, such as CHC (critical hydrogen concentration) necessary to suppress radiolytic decomposition of water as well as the role of water radiolysis as a driving force of “macro-cell! corrosion is structures. This field of science is also closely connected with high temperature electro-chemisry. In spite of the brilliant progress in these field of science, its application to nuclear engineering arena has not been performed well compared with the computational fluid dynamics, for example.
The Fukushima Daiichi accident has revealed significant roles played by hydrogen produced through water radiolysis. Unfortunately, there are very few scientists and engineers who are prepared to cope with the accident management from this point of view. I believe these two field of science should have been a part of basic education in nuclear engineering courses just as the reactor physics.
(55) Environmental monitoring stations in the sea
In trying to assess Fukushima Daiichi accident consequences, it was disappointing to find no radiation monitoring data from the eastern direction from the plant, when the large lease occurred through hydrogen explosion but when the wind direction was towards the ocean. Due to the increased environmental consciousness, the ocean should not be considered as a sink of radiation release. Therefore the monitoring station in the ocean. However, the Eastern Great Earthquake experience imposed serious damage to the lighthouses either constructed on the shore line as well as in the ocean. Among the 251 lighthouses located in the coast line of eastern Japan, 121 of them were destroyed by the tsunami. Therefore, it is not anticipated to be easy. A practical solution should be investigated. On this issue, I have proposed to install a radiation monitoring station on above the reactors. However, it may not be able to detect ground level, low temperature releases. A feasibility of detection from a remote radiation source was discussed also in Earthquake (63).
I. Continued recapping on the status of 1F1 core
Now the TEPCO as well as the Japanese news media are taking the melt down scenario as granted for 1F1. This scenario is now being expanded to 1F2 and 3 as well, and people tend to explain all the difficulties are rooted on this scenario. I am not trying to challenge this notion, although I do not believe we have robust scientific evidence that the gross meltdown occurred as early as on March 11 in 1F1.
I made a quick “back of an envelope” calculation, on top of my recent assessment on reactor water level vs. decay heat curve, to address the issue of accumulation of hydrogen gas in the reactor pressure vessel as well as in the containment vessel. This should help to understand the mechanism of early hydrogen explosion of reactor pressure vessel as well as containment vessel, as well as verify continued needs for hydrogen gas management to prevent another hydrogen explosion. I summarized my results in the attachment, together with the data I assumed for this assessment. In a matter of 10 hours after the reactor trip, as much of 14000 m3-STP of hydrogen can accumulate in the reactor containment vessel, 730 m3-STP in the reactor vessel. These values correspond to 42 and 2.2 tons of TNR-equivalent, respectively. With this much of hydrogen gas accumulated inside of the containment vessel, the continued nitrogen gas charging operation into the 1F1 containment vessel is justified, I believe. As a matter of fact, TEPCO is urgently looking into a route to charge hydrogen into the 1F2 and 1F3, followed with the previous operation in 1F1. At the same time, due to the “internal hydrogen explosion” as occurred in the Hamaoka Unit 1 in 2001, there is a high possibility that the hydrogen gas accumulated inside of the reactor vessels has also be released. Still it is prudent to charge nitrogen also into the reactor vessel to prevent another hydrogen explosion.
II. Tsunami photos
I forgot to introduce a set of photos at the time the tsunami attack released yesterday. It is amazing to see buckling of the huge surge tank by the force of tsunami. I believe such a buckling may have taken place by a large horizontal force induced by the tsunami.
(1) Pictures of Tsunami that hit the Fukushima Daiichi Nuclear Power Station
(pictured on March 11, 2011)-11 photos.
Place: North side of Radiation Waste Treatment Facility taken from 4th floor
(2) Pictures of Tsunami that hit the Fukushima Daiichi Nuclear Power Station
(pictured on March 11, 2011)
Place: The slope at the eastern side of Radioactive Solid Waste Storage Facility (The east side of Unit5 taken from the southern side of the unit) Taken by: TEPCO's affiliate company-6 photos
Well, let me stop here!
(Previous e-mail sent at11:29 PM on May 19 as Earthquake (69) with Summary-Hamaoka Unit 1 Pipe Rupture.pdf)
I. “Stop that reactor accident, please!”
Following the human inspection at 1F2 made yesterday, two TEPCO staffs entered into the 1F3 reactor building for just 10 minutes to investigate dose rates as well as working environment. They were wearing mask with air bomb, special tungsten woven jacket, under the radiation protection suits. They received 2-3 mSv of accumulated dosages. The dose rate was 160 to 170 mSv/h near the personnel hatch to the containment building. They could also walk around the biological shield surrounding the containment vessel. The high dose rate was 50 mSv, but low was within a few mSv. They found that the floor was wet at three spots, but in some place water is leaking down from the ceiling. Although the TEPCO explains this rainfall as condensation of pool water, I think it is a positive proof that the “internal hydrogen explosion” occurred and induced some damage to the piping of RHRS, through which water injection operation is being performed. The basis of my view is summarized in the attached one page summary.
The significance of this accident was in the fact that a hydrogen explosion occurred during normal operation due to accumulation of hydrogen gas generated through water radiolysis, blasting 165 m/m dia pipe with wall thickness of 11m/m. During the normal operation, the hydrogen gas induced by water radiolysis is removed at the turbine condenser, using an ejector and recombined into water, filtered, before discharged into the environment. In an event of station blackout, the active hydrogen removal system is not available. Since there is no way to stop the water radiolysis, the hydrogen gas keep accumulating inside of the reactor vessel and in the containment vessel. If the water level decreased to expose the fuel into the steam, it is very likely that the overheated fuel can ignite the accumulated hydrogen gas. I am calling this as “internal hydrogen explosion.” At the case of Hamaoka Unit 1, the resultant pipe break occurred at the top level of the reactor vessel connected to the RHRS. This line is being used in Fukushima 1F1-3, I believe, for water injection. If we check the heat balance of water being injected with the current decay heat, the flow rate is a few to several times more necessary for removal of the decay heat. Obviously, most of the water is simply leaking before reaching to the reactor vesssel.
(2) Photos of the first floor of 1F2 taken yesterday.
The following photo tells how the staff entry was performed to 1F2 yesterday.
Wel. Let me syop here today!
(Previous e-mail sent at1:40 PM on May 18 as Earthquake (68))
I. “Stop that reactor accident, please!”
On May 18, 4 TEPCO staffs entered into the 1F2 reactor building just for 14 minutes to investigate dose rates as well as working environment. They were wearing mask with air bomb, special tungsten woven jacket, under the radiation protection suits. The worker entry was necessary, since a “PackBot” investigation made in April 18 discovered very high humidity level, prevented detailed investigation. The workers received 3-4 mSv of accumulated dosages, with the highest of 4.47 mSv. The areal dose were 50 to 10 mSv/h. TEPCO presume that a major portion of the steam is coming from the spent reactor pool, therefore, an air cooling system is planned to be installed as soon as possible.
The un-stable situation still persists in 1F3. TEPCO presumes that the molten core debris are plugging the core shroud region, blocking the water to the reactor vessel. As I am going to explain in the next section, the leakage is very likely through cracks due to the “internal hydrogen explosion.” This type of hydrogen explosion has been preceded by the Hamaoka Unit 1 in 2001. The DEB occurred at the Residual Heat Removal System, in a pipe line connecting from the main steam pipe to the RHR heat exchanger ( http://kokai-gen.org/information/7_032-hamaoka.html#hazime, in Japanese).
II. Continued recapping on the status of 1F1 core
Now the TEPCO as well as the Japanese new media are taking the melt down scenario as granted for 1F1. This scenario is now being expanded to 1F2 and 3, and people tend to explain all the difficulties are rooted on this scenario.
I do not believe we have robust scientific evidence that gross meltdown occurred as early as on March 11 in 1F1. Following my “back of an envelope” modeling study, I made some improvement to be more realistic, as well as to apply this model for further study. Attached please find the updated version of the memo I attached yesterday in Earthquake (67). The improvements and further studies are:
(1) The cross section of the reactor pressure vessel is updated to include the smaller area in the core region;
(2) Effects of removing the decay heat by decreasing ミ5%.
(3) Effect of the media reported suspension of ECCS before arrival of the tsunami.
Further explanation is added as remarks in the three page attachment.
Through this study, I confirmed that on of the most important issue is how long the water level in the reactor pressure vessel was maintained after the seismic trip. I tried to find some information in the plant data released from TEPCO yesterday, however, I have not been successful in this regards.
However, I confirmed that the TEPCO’s conclusion should have resulted through omitting the “feed and bleed” operation, which was supposed to be an essential safety provision incorporated in the light water reactors in the light of the TMI accident. After omitting this, TEPCO concluded that the water level should have been down to the bottom of the reactor pressure vessel in three hours, at around 6 PM on March 11, by assuming the total loss of cooling capability with the arrival of the tsunami. In my estimation, the the water should have lasted at least for around ten hours, as long as I used the key dates released so far by METI.
However, I also share TEPCO’s view that there must be a leakage from both the containment vessel as well as in the reactor vessel. This I believe is through cracks in the piping,due to the “internal hydrogen explosion” and not through the meltdown. This mechanism of failure is in accordance with the double ended pipe rupture accident in Hamaoka Unit 1, at November 7, 2001.
In this regard let me also show another evidence as attached in 1F2-May 15 event. In the file, both the reactor pressure vessel and dry well pressure surge were recorded, followed with an increase in dose rate in the dry well. However, the detected dose rate was only 140 Sv/h, not in support of the meltdown scenario.
Nevertheless, it is very strange to see TEPCO all in a sudden changed their footing to the meltdown scenario almost two month from the event. It is far more important to keep cooling the damaged core. From this point of view, the “internal hydrogen explosion” is a very serious issue, since most of the water pumped to the reactor vessel are leaking out before reaching to the reactor vessel.
Well, let me stop here.
Date: Tue, 17 May 2011 22:17:49 +0900
Subject: Earthquake (67)
From: Genn Saji
Remarks on TNT-equivalent value:
Many people were interested in my illustrative TNT-equivalent value. One of the follower called my attention to the difference between combustion and detonation. He wrote me tat the 4% by volume is the combustion threshold for hydrogen in air, not detonation. This would be more in the region of 10% by volume (8% is the downward flame propagation threshold believed to have existed in the TMI containment prior to the ~200 kPag pressure peak observed). It may be so, however, I hope someone will do a computer simulation of the reactor building devastation such as done for a hydrogen gas station for automobile in the following website (although the site is in Japanese, the deformation of a concrete building by hydrogen explosion is very interesting.
I. TEPCO released the Fukushima 1F plant data
Late yesterday, TEPCO disclosed their plant data. The data consist of:
(1) Recorder charts
(2) Alarm records data
(3) Operators’ logs
(4) Process computer records
(5) Transient record data
(6) Operators’ action records
Due to the station blackout, the process computer records contained only for 1F2. At the time of tsunami arrival, the most of the instrumentation stopped working. Although the available data are sparse and hard to decipher, we have to consider it is a miracle to see these data somehow recovered. Some of the data became available by dispatching auto batteries for the operators to supply power for instrumentation and control. I think it will take sometime for us to understand the contents of the released data. Practically all the data are “raw data.” Although the data were all in Japanese, let me attach the address ( http://www.tepco.co.jp/nu/fukushima-np/index10-j.html )
II. TEPCO updated their road map for recovery
TEPCO made no change as to the overall time schedule, however, they changed the “water sarcophagus” into recirculation of the contaminated water accumulated in the reactor building after purification by using the water treatment facility soon to be start constructed.
III. Further recapping on the status of 1F1 core
The melt-through analysis released yesterday provoked many arguments among Japanese scientists. Also, the interpretation of the TEPCO’s press release are all different in tone among journalist, however, most of them accepted as released. TEPCO released the following Power Point summary of their assessment of the status of the reactor core. According to the TEPCO’s press release ( http://www.tepco.co.jp/en/press/corp-com/release/11051509-e.html ), the total loss of cooling capability assumed to have occurred with the arrival of the tsunami. This leads them to a conclusion that the water level should have been down to the bottom of the reactor pressure vessel in three hours, at around 6 PM on March 11. In one and half hour later, the fuel started destroyed, by heating up to a temperature reaching as high as 2800 degree-C. In 16 hours after the earthquake, at around 6:50 AM of March 12, practically all of the fuels were melted down to the bottom of the reactor vessel.
Yesterday, I pointed out that it is not clear whether a cooling effect of “feed and bleed” cooling, at least “bleed” portion has been considered or not in the TEPCO’s viewgraph. The “bleeding” means evaporation of the reactor water by sacrificing the water inventory, To check whether the “bleeding” effects are included or not, I made a “back of an envelope” calculation as attached. The model starts with the 1F1 decay heat by using an empirical equation, which is close to the ANS 5.1 curve. By nature, it is for safety assessment, and looks to include approximately 10% of margin from the more detailed calculation as provided by Professor Kazuhiro Oyamatsu. Although the difference is not so large, however, it makes a large difference for predicting the water level at one day or so after the reactor shutdown. Since this is just to confirm the effect of “bleed” cooling, I assumed a cylindrical reactor pressure vessel with an inner diameter of 4.8 m, filled with water up to 5 meters from the top of the fuel assembly. Also assumed that after reactor trip, and even after the arrival of tsunami, the water level is kept at least until 16:36 as released from METI. It is reported today that the ECCS was turned off for about 3 hours, since, perhaps, the cooling rate exceeded a golden number of ミ50% an hour for the cooling rate arrowed for a large structures. This suspension of cooling is not so serious, as long as the water level has been recovered by restarting the ECCS. Since there remained other means to inject water. It is not clear when it became impossible to inject water. Therefore, I treated this issue as a parameter. The TEPCO made an assumption that the cooling function was lost upon arrival of tsunami, arrived about one hour after the reactor trip, whereas I made an assumption that it get lost at 16:36 or later. TEPCO’s result, predicting that the water level went down to the core support plate level in just three hours is overly conservative, I believe. Depending on the accuracy of he decay heat curve as well as the time of “loss of water injection,” it may have survived until later next day. Note that there is a mark at 5:50 with a remark that a pure/sea water injection was started. However, if there was a delay in sea water injection, this must have induced a serious difference.
Well, let me stop here tonight,
(Previous e-mail sent at10:02 PM on May 16 as Earthquake (66))
I. Further recapping on the status of 1F1 core
For last several days, the Japanese news media are repeatedly introducing stories with headlines such as “TEPCO finally admitted the core melt down!”. TEPCO released the following Power Point summary of their assessment of the status of the reactor core. ( http://www.tepco.co.jp/en/press/corp-com/release/11051509-e.html ) According to this report, TEPCO’s understanding was made through an analysis, by assuming the total loss of cooling capability with the arrival of the tsunami. This leads them to a conclusion that the water level should have been down to the bottom of the reactor pressure vessel in three hours, at around 6 PM on March 11. In one and half hour later, the fuel started destroyed, by heating up to a temperature reaching as high as 2800 degree-C. In 16 hours after the earthquake, at around 6:50 AM of March 12, practically all of the fuels were melted down to the bottom of the reactor vessel.
Well, although this kind of analysis is important, however, it is dangerous to be driven away only by the reading of level gauges. The accident scenario as I can compile from the official press releases are as follows;
(1) For about one hour after the earthquake, arrived at 14:46 on March 11, the 12 out of 13diesel generators started as designed. The reactors must have been cooled by High Pressure Spray Cooling System later by employing the Low Pressure Water Injection System, The successful operation of these ECCS systems cooled the reactor core as designed.
(2) Tsunami, arrived at 15:42, induced “station black out” as well as “loss of ultimate heat sink” accident. In this phase, the first system to start up automatically was the turbine driven Isolation Cooling System. However, its safety function was seriously degraded since it could not remove heat by using its heat exchangers (emergency condensers), which need Reactor Component Cooling Water System and Sea Water Pumps (a part of the ultimate heat sink), which was designed to supply sea water to the Reactor Component Cooling Water System. Therefore, the system discharged hot steam directly into the suppression pool water.
(3) At 16:36 of March 11, the water injection to the reactor vessel failed, perhaps because of the battery supplying to this system (Partition I) drained. This also may have resulted in a failure of the Shutdown Cooling System, connected to the same DC125 Volt Bus A ( Partition I ).
(4) It was reported in a news media that the critical time limit for all batteries to be drained was around 22:00 on March 11. However, in a reality, some of the essential DC bus kept working until overnight.
(5) As long as the battery power is available, the reactor vessel pressure was automatically started releasing steam overpressure from the reactor vessel, through Automatic Release and Safety Valve System, into the suppression pool. Even without the battery power, the safety valve function can release steam directly into the suppression pool water. Due to no heat removal, the suppression pool water temperature gradually started to rise, until it reached to the boiling point of pool water at 0:45 AM of March 12. From the time of loss of feed water flow, at 16:36, the reactor vessel water level started to decrease, by initiating only the “bleed” cooling, without “feeding”. It is not clear whether this cooling has been considered or not in the TEPCO’s viewgraph. Perhaps not, considering their simplified modeling, which looks more like an adiabatic calculation, resulting in a very conservative result. In addition, since there is another pump in the Residual Heat Removal System B connected to DC125 Volt Bus B ( Partition II), the water injection may have been possible. This can only be clarified when the operators’ log book is released in the future.
(6) Pure water injection started at 5:50 AM of March 12.
(7) Containment venting started at 10:17 on March 12.
(8) Hydrogen explosion at 15:36 on March 12.
(9) Sea water injection started on 20:26 on March 12.
Therefore, only the TEPCO operators should know well whether the water injection was totally impossible starting from 16:36 March 11 until 5:50 AM of March 12. However, previous explanation by TEPCO was reported that the reactor core was uncovered with water only at the top 1/3 portion of the fuel assemblies. Perhaps change of their assumption is induced by their new level gauge readings, after re-calibrating it several days ago. It appears that the whole scenario depends on the level gauge reading. The current phenomenological observation does not support the scenario of the total core melt and flowing down to the bottom of the reactor pressure vessel as early as on the morning of May 12, I believe.
One good news was, by increasing the water injection flow rate to 10 tons per hour, increased from the previous 8 tons per hour, the temperatures went down to 95.1 degree-C at the feed water nozzle, from the previous 110.4 degrees at 11 AM of May 15. The reactor is close to the cold shutdown status, although no ultimate heat removal provision is available.
II. Further recapping on the continued unstable situations in 1F3
The temperature around the reactor vessel has been gradually increasing. At the reactor vessel seal bellows, the temperature increased to ????? degree-C on May 9 from 99.6 degree-C on May 1, also at the lower portion of the reactor vessel, increased to 154.3 degree-C from 116.5 degree-C. Following this temperature surge, TEPCO re-routed the flow passage to the feed water line so that the water can be directly injected into the reactor pressure vessel as well as increased the flow rate. After that, there is a general trend of decreasing in the temperature.
The highly contaminated water continue to be a critical issue in 1F3. There are approximately 22000 tons of water accumulated in the basement of the turbine hall and the trench. In view of the immediate risk, TEPCO has been preparing to use another building, which is located at the Central Waste Management Facility, by waterproofing the underground portion for storage. Also, a branch piping was prepared to pump the contaminated water in addition to the water being pumped from the 1F1 trench.
III. A memo for lessons learned from the tsunami-induced nuclear disaster (continued)
For memory sake, let me add lessons learned.
(53) Intrinsic safety against radiolytic decomposition of water
The magnitude of the severe accident and its sequence depends strongly on the intrinsic safety of the reactor, the safety provisions in place as well as operational issues. For example, the Chernobyl accident was induced by the specific features of the RBMK type reactors. The accident was initiated due to the vulnerability of the graphite-moderated water-cooled channel type reactors, combined with the positive void coefficient and violation of an extended low power operation by bypassing the ECCS. The reactor power began to increase by pushing the ‘AZ-5’reactor shutdown button, inducing sudden boiling of the reactor coolant at the bottom of the reactor. This resulted in supercriticality thereby increasing the reactor power b several dozen times. The energy input to the fuel was so large that Zr cladding was molten at lower portion of the fuel rods, and the UO2 fuels were disintegrated into fine particles which were discharged from the channel resulting in a subcritical core state. (G. Saji, 2005. Management of Nuclear Risks by Intrinsic Safety, Siting, and Defense-In-Depth for Future Reactors: Lessons Learned from the Chernobyl Accident. In: PSA’05 conference CD. International Topical Meeting on Probabilistic Safety Analysis, PSA’05, 11-15 September 2005 ・ Sir Francis Drake Hotel, San Francisco, California, USA.
Likewise, the development of the accident strongly influenced by an lack of BWRs’ intrinsic safety against radiolytic decomposition of water. The hydrogen generated through the water radiolysis is designed to be removed from the water by ejectors and oxyduzed to water through catalytic recombination process, which depends on many active components. This was considered to be adequate, however, in an event of station blackout, these active components all became out of service and could not perform the intended safety function. This must be the root cause of leakage of the water injection piping at the Fukushima Daiichi, through an “internal hydrogen explosion”, the precedence of this phenomenon has actually occurred at the double ended pipe rupture accident in Hamaoka Unit 1, at November 7, 2001. A series of the sudden pressure drops observed during the early phase of Fukushima Daiichi accident are very likely due to the “internal hydrogen explosion.” This is currently making the recovery operation very difficult by leaking water intended to be injected into the reactor vessels. The large leakage of water is aggregating the accident management, through an increase in the total volume of contaminated water.
The intrinsic safety of BWR plants can be improved by using a hydrogen water chemistry, by dosing a small amount of hydrogen to improve corrosion issues. The drawback of this issue is in an increase in radiation in the turbine hall area through N-16 in the primary water. Although the current objection of the hydrogen water chemistry is for reduction of corrosion issues, especially SCC (stress corrosion cracking), it should be further investigated to go beyond the CRC (critical hydrogen concentration), which is the minimum concentration of dissolved hydrogen required to prevent the net raiolytic breakdown of the water. Radiolysis is said to be in suppression when there is no net decomposition of the water due to the addition of excess hydrogen.
In PWRs as well as in VVERs (with the ammonia water chemistry), through dosing with a sufficient amount of hydrogen into the primary water, the effect of radiolytic decomposition of water was not so large, as shown by S. Gordon, K.H. Schmidt and J.R. Jpmlamp, An Analysis of the Hydrogen Bubble Concerns in the Three-Mile Island Unit-2 Reactor Vessel, Radiat. Phys. Chem. Vol, 21. No. 3, pp. 247-258, 1983.
(54) Early soil sampling data
The Japanese Ministry of Education, Culture, Sports, Science and Technology, "MEXT", started to measure soil samples to detect other nuclear species, other than Cs-134, Cs-137 and I-131, two months after the accident. This is well too late to be able to account for a complete picture of released radioactive species in the environment. Early sampling, especially within the first few weeks is indispensable to identify major radiation species released into the environment. For radiation health assessment, a complete picture of nuclear species involved is indispensable.
Well, let me stop here.
(Previous e-mail sent at1:16 AM on May 16 as Earthquake (65))
I. Further recapping on the status of 1F1 core
Late today, TEPCO made a press interview to explain the status of 1F1 core. According to their analyses, 1F1 core appears to melt down soon after arrival of the tsunami, nd accumulating on the bottom of the reactor vessel. TEPCO also added that since the reactor vessel temperature is kept around 100-120 degree-C, it is unlikely that another large releasewill occur.
Well, I have also been struggling to understand the mystery of the 1F1 situation, where a molten core is postulated at the bottom of the reactor vessel being kept at around 100 ミ120 degrees-C. However, I am more and more becoming confident that a series of “internal hydrogen explosions” must have occurred during 11 ミ 15 March, making cracks around the isolation valve and outside of the containment vessel. The injection of water into the reactor vessel is being performed through a few systems, and perhaps the water is leaking through the cracks. Only a fraction of water is successfully injected into the reactor vessel, others simply leaked out into the reactor building, preventing an increase of the water level inside of the containment vessel.
Mt view is based on the hydrogen explosion accident at Hamaoka Unit 1, occurred on November 7, 2001. A pipe rupture accident occurred, inducing a double ended break of a 165 mm diameter, 11 mm thick piping during normal operation. The DEB occurred at the Residual Heat Removal System, in a pipe line connecting from the main steam pipe to the RHR heat exchanger ( http://kokai-gen.org/information/7_032-hamaoka.html#hazime, in Japanese). The hydrogen and oxygen accumulated in a section of pipe route which became an “air (hydrogen) pocket,” with reversed U shape layout. The operator were trying to perform routine manual startup test of ECC as required by the Technical Specification.
This accident is very important, I believe, since the hydrogen explosion may take place during normal operation in BWR, where the hydrogen generated through water radiolysis is being removed by an ejector to be released into the atmosphere through recombiner. After shutdown, the Burnable Gas Concentration Control System circulate the steam inside of the reactor vessel, through re-combiner back to the suppression pool water. With station blackout, there is no way to remove hydrogen accumulated inside of the reactor vessel. There is no way to stop the hydrogen and oxygen generation through water radiolysis. In a day or so, the reactor vessel is spontaneously filled with hydrogen and oxygen. In general, reductive radical species, generated by water radiolysis, produces hydrogen, whereas oxidative radicals produces hydrogen peroxide, which decompose into oxygen and water. It is generally known, that irradiation of pure water with low-LET radiation leads to the establishment of a steady state in which low concentrations of hydrogen, oxygen and hydrogen peroxide are present. (page 253 of Spinks and Wood, an Introduction to Radiation Chemistry, Third Edition, John Wiley and Sons, Inc. (1990). In a severe accident situation, how the radiation chemical behavior follows are not known, however, the Hamaoka Unit 1 pipe rupture accident warns us that the upper portion of the reactor vessel can become a “hydrogen pocket”.
I tried to identify occurrence of the “internal hydrogen explosion” by plotting the RPV pressure and DW pressure during 12-16 March. I am shocked to find that there are several events of sudden pressure drop in each of Fukushima Daiichi as attached. These events are likely related with the “internal hydrogen explosion”. I also tried to correlate these events with the environmental monitoring record, Monitoring-Events curve, distributed with Earthquake (63), updated in (64). The results are not so conclusive. Perhaps it is necessary to combine with radiation monitoring data ( CAM ) to conclude whether these data are related with other measurement.
In conclusion, although I share that the injected water may not be
II. Further recapping on risky situations in 1F3
Since the reactor vessel temperature is gradually increasing, TEPCO rerouted the water injection water passage and increased the flow rate to 15 tons per hour, however, the temperature is still surging. TEPCO added boron to prevent re-criticality, since the salt water is now replaced into pure water. TEPCO announced that the injected water is still leaking and further examination is in progress.
If the water leakage is from the some of the large pipes related with ECCS, due to the “internal hydrogen explosion”, as explained above, the re-routing may not have been effective.
Well, let me stop here tonight!
Date: Sun, 15 May 2011 01:01:42 +0900
Subject: Earthquake (64) with a correction of TNT-equivalent
From: Genn Saji
CORRECTION for Earthquake (63)
Let me apologize repeating the same stupid mistake, slipped in by copying some data from my Earthquake (9) as to the hydrogen explosion limit of 4%, which was corrected in Earthquake (10). The explosion limit should have been 4% [volume %], not [mass %]. Let me update the relevant portion of Earthquake (63) as below:
1. Assume a 25 meter radius of a spherical source volume formed on top of the 1F1 reactor building, with a volume of 65, 420 m3. This is just an a-priori guess, by referring to the size of the Fuel Handling Room on top of the reactor building with 30,000 m3 or so. Although this is not an essential assumption, the hydrogen detonation concentration of 4% [volume %] amounts to 1200 m3 of hydrogen in the 30,000 m3 of air. Since the heat released by hydrogen is 141.8 kJ/g, the hydrogen explosion energy is equivalent to approximately 4 ton-TNT (I ton of TNT releases 4.184GJ). This energy release is 1/10 of that of the Chernobyl accident with 30-40 TNT-equivalent, although the Chernobyl explosion was through a steam explosion (but not nuclear explosion). With this much of thermal energy released, it could have produced a semi-spherical steam volume as large as 0.8 km in radius, as in the case of the Chernobyl accident (G. Saji, 2005. A Scoping Study on the Environmental Releases from the Chernobyl Accident (Part I): Fuel Particles, PSA’05). However, most of this energy was consumed by blasting the reactor building. The spherical cloud I watched in TV was not so large compared with the size of the building. Therefore 25 meter radius.
I. “Stop that reactor accident, please!”
(1) Temporary cover on top of the 1F1 reactor building
I forgot to include this press release yesterday. TEPCO announced yesterday that a temporary cover will be installed around the 1F1 building. It is to recover a portion of the secondary containment system, by preventing release of contaminated dust to the environment. It is reported that a filtered ventilation will also be attached to the cover. This may be able to reduce the particulate release at least by 90-99%. The cover is made from steel frame, prefabricated, covered with polyester sheets. The structure will be brought in by assembling partially to reduce the worker doses. TEPCO already started to remove debris around the building to provide working space for big crawler cranes. Actual construction will be started in June.
The cover can only be placed after reconstructing the air cooler systems for both the reactor containment system as well as the spent fuel pool, I believe.
(2) A large volume of water found in the 1F1 reactor building
TEPCO announced today that a worker discovered a large volume of water in the basement of the Reactor Building, accumulated as much as 3,000 tons of water with a level of 4.5 meters from the floor level of the basement. The height of the basement is 11 meters. From their description, the room corresponds to the “triangle corner” located around the corner of the Reactor Building. According to an illustrative drawing in the PSAR, there are stairways to the basement from the operational floor of the Reactor Building. The dose rate near the stairway was 72 mSv/hr,
Although media reports, based on the TEPCO’s announcement, are all directing towards leakage from the containment vessel, I believe this is much less likely due to this observation. The “triangular corners” are isolated room from the biological shielding surrounding the containment vessel. If the leakage is directly from the containment vessel, it should have filled up the cylindrical portion, located at the center of the Reactor Building. Moreover, the dose rate is far less than what is expected, if the leaked water is directly from the containment vessel. At the bottom of the “triangle corner” the DHRS pumps are installed. I am more towards leakage from the piping connected with the water injection into the reactor Pressure Vessel, since it is said that the water injection is through a few other auxiliary systems.
However, this issue is more serious for me. When the water level further increase to the operational floor level, the contaminated water can leak out from the track entrance double door. Also there is a main steam pipe tunnel going into the turbine hall. When the water level goes too high, the water may spill into the turbine hall. Since the residual water holdup capacity is less than 5000 tons, there is less than 50 days left before leaching this critical level, since as much as 4 tons per hour out of 6 tons per hour of water can be leaking in to the basement. I have to watch with my finger crossed.
II. Contamination of freshwater fish
Early this morning, it was reported that sampling of two different kinds of freshwater fish in Fukushima Prefecture were found contaminated in a news media. The fish samples were “ayu” ( Plecoglossus altivelis altivelis ) and “kawasagi” ( Hypomesus nipponensis ), each found with 720 Bq/kg and 870 of radioactive cesium. Currently catching these kinds of fish are not permitted for preservation purposes, there should be no concern to the possible human food chain. However, I have been watching this issue carefully, since the river locations were in the down stream of the Abukuma mountain chains where there are heavily land contaminated corridor region spreading towards the NW direction of the Fukushima Daiichi. The deposited contamination should have been washed down to the river by rain. Fortunately there is not much of Sr-89 and 90 released this time, the kind of health effects may not be repeated as observed in the Techa River near Mayak pultonium production facilities in Russia. However, it is necessary continue monitoring the extent of contamination in the freshwater stream flowing down from the highly contaminated region.
III. Recapping on the release fraction using soil sampling data
On this issue, I introduced an attempt to account for the release fraction, on Earthqukae (57) and (59). This is targeted to provide Table 2 Estimates of the principal radionuclides released in the accident, in Table 2 of the Annex J of UNSCEAR 2000, by grouping into noble gases, volatile species, intermediate and refractory materials. NEXT started to release their soil sampling data beyond I-131 + Cs-134 and 137, starting May 9. I looked into the new data to update the release fraction estimation as attached. However, I discovered that it was too late, since most of the short half-life radionuclides are decayed away by now and it is too much of correction necessary to estimate the concentration at the reactor shutdown, if ever detected. In addition, the release of radioactive species was performed after going through the suppression pool water, the release fractions of intermediate and refractory materials are a few orders of magnitudes smaller as compared with the Chernobyl releases. This is making detection of other radioactive species, other than I-131 + Cs-134 and 137 much difficult as compared with the Chernobyl. I am increasingly pessimistic to account for a comprehensive picture of releaseseven for 1F1. The similar sampling data for 1F2 and 3 are almost none, since both of them released the contamination towards the south or east direction, without leaving foot prints of land contamination.
Well, let me stop hear.
((Previous e-mail sent at 9:56 PM on May 13 as Earthquake (63))
I. Recapping on the status of 1F1 core
Today, at the press interview in the morning, Mr. Nishiyama of NISA expressed his view that the “submerging operation” (previously called “water sarcophagus” operation) may not be an essential issue, as long as the fuel cooling is available. Nevertheless, it is necessary to increase the water level of the containment vessel so that the cooling water pass to the external heat exchanger can be secured, he added. I think this is a more reasonable approach, since the “water sarcophagus” operation does not solved the cooling issue.
In this connection, I am increasingly concerned that a portion of the feed water may be leaking form somewhere into the basement of the turbine hall from the water line. It is because, the magic number of the current water injection, 6 tons/h , should be able to remove 3.8 MW of decay heat through vaporization. The empirical decay heat curve, such as ANS-5.1 1973 (Decay Energy Release Rates Following Shutdown of Uranium-Fueled Thermal Reactors Draft ANS-5.1 / N18.6, October 1973) is predicting that the current decay heat should be about 0.4%, which is equivalent to 5.5 MW, 40% in short in water injection rate. Unfortunately, the decay heat curve in the medium to long term cooling is not well established, since we did not care in system design which requires only a short term decay heat curve typically a week or so. As a matter of fact, Professor Kazuhiro Chikamatsu recently provided me with his calculation of the decay heat predicting as low as 0.075%(approximately 1 MW) by closely following the fuel shuffling sequence of the 1F1. Since neutron captures are not included in his program, the results can be smaller by 20% or so. The decay heat estimation can be off by factors in this region when we used the empirical equations.
The current stable core cooling established in 1F1 indicates that the heat balance is OK, however this does not mean that the 6 tons per hour of injected water is actually flowing into the core. It can mean that only a portion of it is being injected, if we trust more realistic decay heat. This may explain why as many as 9000 tons of water has been injected into the reactor pressure vessel. However the water level inside of the containment vessel does not seem to be increasing, although no venting has been performed since March 12. The water can be leaking out before actually injected into the reactor vessel. This seems to be the case in 1F3.
II. Continued recapping on the accident scenario by referring to the SPEEDI results
On this issue, by Earthquake (58), Earthquake (61) and again on Earthquake (62), I introduced a graphical representation of the monitoring data, displayed daily from March 12 to 15. Although a few large releases are recorded everyday, they are not well correlated with the reported major events, such as initiation of containment venting, hydrogen explosion, etc. The current status in the following:
(1) Any of the four hydrogen explosions were not recorded in the environmental monitoring facilities, temporary installed by TEPCO at the most critical time of the accident.
(2) Venting appears to be detectable, although not always. When detailed operators’ log book disclosed in the future, we should be able to make further checks. Since the venting resulted in ground-level release, it is easier to detect them.
(3) If a surge of dose-rate is detected without directory related operator actions, this may indicate a presence of “spontaneous” venting, i.e. failures of containment vessel.
(4) TEPCO’s “compiled data” may have removed some of the essential information in the course of the accident. It is strongly requested to release both the “compiled data” as well as “raw data”.
The most serious issue for me is in Point (1), namely why the gigantic releases evaded detection as the result of hydrogen explosions. So I made the following “back of an envelope” assessment to understand why the environment monitoring stations could not detect the hydrogen explosion and resultant radioactive plume passages. I assumed the following illustrative model.
(1) Formation of a spherical source volume
1. Assume a 25 meter radius of a spherical source volume formed on top of the 1F1 reactor building, with a volume of 65, 420 m3. This is just an a-priori guess, by referring to the size of the Fuel Handling Room on top of the reactor building with 30,000 m3 or so. Although this is not an essential assumption, the hydrogen detonation concentration of 4% results in 1200 m3 of hydrogen in the 30,000 m3 of air. Since the heat released by hydrogen is 141.8 kJ/g, the hydrogen explosion energy is equivalent to approximately 4 ton-TNT (I ton of TNT release 4.184GJ). This energy release is 1/10 of that of the Chernobyl accident with 30-40 TNT-equivalent, although it was through a steam explosion (but not nuclear explosion). With this much of thermal energy released, it could have produced a semi-spherical steam volume as large as 0.8 km in radius, as in the case of the Chernobyl accident (G. Saji, 2005. A Scoping Study on the Environmental Releases from the Chernobyl Accident (Part I): Fuel Particles, PSA’05). However, most of this energy was consumed by blasting the reactor building. The spherical cloud I watched in TV was not so large compared with the size of the building. Therefore 25 meter radius.
2. Assume a spherical surface source of 2.4% of the shutdown core inventory in Cs-133, 134, 136, and 137 as well as I-131 and 133. This assumption is based on my estimation of the release fraction from the land contamination map as provided by US DOE/NNEA, in collaboration with MEXT, as reported in Earthquake (61).
(2) Radiation source ミ dose calculation
Assumed the following:
- Equivalents of one Sv of X- or Gamma radiation = 6.77E+02 MeV absorbed per cm3 of air.
- Energy absorption coefficient mu = 3.35E-5 cm-1
- distance form the plume to the detector: Z meter
- Dose rate: D(sphere) = Sa/2x(25-Z)/(25+z)x(exp(-mu x (Z-25)) - exp(- mu x (Z+25)))
- Source density Sa=147.5MeV-PBq*0.000000335/677*3600
Z(meters) 100 200 300 400 500 600 700 800 900 1000
D(mSv/h) 315 31.3 6.9 2.12 0.79 0.33 0.15 0.07 0.004 0.002
This means that I should have looked for the dose rate data as low as several to 100 microSv/h region for the detector located in 700-800 meter region. I revisited the dose rate data on March 12, to correlate with the hydrogen explosion from 1F1. Although I could barely identify a bip of a few microSv around the time of explosion, however, it does not positively support a significant increase in the dose rate due to hydrogen explosion. Unfortunately, the wind direction was towards NW and increased the distance from the nearest monitor, making the measurement more difficult.
III. A memo for lessons learned from the tsunami-induced nuclear disaster (continued)
For memory sake, let me add lessons learned.
(52) Decay heat curve in the intermediate to long terms for accident management
We are facing with difficulties in judging the credibility of the decay heat cure in the time span beyond a few weeks to a few years. For the system design, where the capacity is determined at the high side of the decay heat, we have not been paying too much of an attention to the decay heat cure in the intermediate to long terms. Since the decay heat in these region strongly depends on the fuels’ residence time in the core, it is necessary to follow the operational history. As a results, empirical curve assuming infinite burn time such as ANS curve tends to give larger than reality values. Professor Kazuhiro Chikamatsu has been trying to develop a PC program, which incorporates decay and production of as many as 1000 nuclear species. However, the code does not incorporate neutron captures, therefore, his results may be low by 20% or so, according to the author. The standard way to calculate is by ORIGEN code.
Well, let me stop here tonight.
(Previous e-mail sent at 11.27 PM on May 12 as Earthquake (62))
This is a shorter version of Earthquake (62). This is sent again, since I noticed that some of you may have been unable to receive my recent daily updates, perhaps judged as a spam mail. In some case the service provider does not send back the return message for spam mails and I have no way to know whether you are receiving or not. I am sending this by removing all of the previous mails sent before April to reduce the mail size. If you started to receive this daily update, please let me know. I intend to write on top of this starting tomorrow.
Sorry for your inconvenience with my poor IT infrastructure, since I started to inform just my close international friends with what’s happening at Fukushima. Moreover, I was not prepared to continue this long with so much in detail, with so wide forwarding. This daily update is my independent personal opinion and not representing the official information from Japan. Also, I am well aware of may typos, misunderstandings, mistakes and inappropriate expression in English in daily updates, however, I do not have time now to correct these, since I believe continuing this is more important until the things settle down in the future. G. S.
Today, the second group of 70 residents from Katsurao-mura and Kawauchi-mura, both located in the “vigilance (off limit) area within 20 km, had a chance to visit their homes just for two hours. The northern part of Katsurao-mura is directly within the heavily contamination corridor located NW direction from the plant. As a result, the accumulated doses of the villagers were 3-38 microSv, whereas the doses were less than 1 microSv, for those from Kawachi-mura. The latter escaped this heavy deposit of radiation materials. The 38 microSv for two hours corresponds to the upper boundary of Zone IV defined yesterday. This dose experience is consistent with the assessment made yesterday. Perhaps the most exposed individual should have been living in the north end of the village, I presume. No decontamination was found necessary.
I. The status of 1F1 core
There has been many speculative views expressed by various people as to the status of the 1F1 core. However, I have been trying to refrain from such a discussion, since there are very few robust data representing the actual status of the damaged core, except for sampling data, Cs-134 + 137 land contamination data, temperature and pressure around the reactor vessels, etc.
Today TEPCO explained likely that the reactor fuels are dislodged from the normal location further down inside of the reactor pressure vessel. The core debris are still retained in the lower portion of the reactor vessel and being cooled by the reactor water inside. This conclusion was resulted from their recent recalibration of the level gage inside of the reactor vessel, performed on May 10. By correctly setting the zero point, the water level was found ミ5m from the normal level of the top of the fuel assemblies, indicating that the molten fuel went through the core support plate down into the lower plenum region of the reactor vessel. Since the temperature of the reactor vessel is still maintained below 120 degree-C, TEPCO insists that the core cooling is still available somehow by injecting 6-8 tons of water into the reactor vessel, although the level of the reactor vessel did not increase. At the same time some pressure retaining capabilities are also maintained, indicating that not all of the injected water is leaking out. Current temperature is 92.7 degree-C at the lower portion of the reactor pressure vessel, 114.7 degree-C at the feed water nozzle of the reactor vessel, located in the upper portion.
This press release is puzzling for me. The cold temperature at the lower portion of the reactor pressure vessel and the red hot molten fuel at the bottom of the reactor vessel are not a compatible image. It is the same situation at the time of the TMI accident without having a reliable instrument to measure the level of water in the core. Although much studies were made, there have been no good solution to replace the level measurement by differential pressure gauges. In BWR, this issue is also very complex, since the reference pressure, the zero point, is provided at the top of the reactor vessel, through the condensing pots, which are supposed to be filled with water supplied by self-condensation of steam. Once the reactor vessel is overheated without steam flow, it was not clarified how will the reference pressure behave, although I asked to a BWR instrumentation designer at the early stage of this accident. It is a golden rule not be carried away by depending on just one instrumentation reading for the accident management. How about the radiation monitor located inside of the containment vessel. I believe “water sarcophagus” is not the final goal. Keep cooling the damaged core is the most important mitigation of the consequence of the accident.
Without being able to confirm the actual state of the damaged core, it may affect TEPCO’s roadmap, which is said to be updated in May 17.
II. Further recapping on the accident scenario by referring to the SPEEDI results
On this issue, by Earthquake (58) and again by Earthquake (61), I introduced a graphical representation of the monitoring data, displayed daily from March 12 to 15. Although a few large releases are recorded everyday, they are not well correlated with the reported major events, such as initiation of containment venting, hydrogen explosion, etc. I was puzzled with the results. However, one of my Japanese friends told me that METI has changed the time of venting from 1F1 on March 12. By making this correction, the venting at 10:15 matches the large increase in the dose rate around this time.
Another friend of mine also informed me a presence of a set of raw environmental monitoring data, before integrating them into the unified format now used by TEPCO. It appears that there were some data management problems inside TEPCO and the official data being released failed to compile correctly the raw data into the new data format. Attached please find the updated graphical representation. The new graph for March 13 is presented in the second page, using a raw data measured every two minutes during the critical periods. It appears that the new March 13 graph looks more reasonable as compared with the graph made from the TEPCO’s official press release. It is now well correlated with the “8:41 1F3 Venting started event, however, two other two peaks in the dose rate are still not well accounted for, as well as the reported “11:00 1F2 Venting started” operation. If the large dose rates are not correlated with operator’s action, it may indicate a presence of “spontaneous venting”, therefore continued careful assessment is still necessary.
In the light of this finding, I started to feel a necessity of revisiting the similar data for March 14 and 15. It appears that TEPCO is trying to clean up the raw data to look neat, by displaying every 5 or 10 minutes for example, however, this process may have removed the important characteristics of the releases. The curves, plotted by using the TEPCO’s “official” press releases, look smoother, which may not represent the real situation. This issue seems to be a negative effect of NISA’s strong protest ordering TEPCO to release sampling data with more care at the time TEPCO tried to update the data. Also, I have to add that after the first explosion, sometimes some of the radiation monitoring data are showing strange results, perhaps due to radiation from debris. A careful screening of the data is necessary.
Well, let me stop here.
Date: Wed, 11 May 2011 21:21:27 +0900
Subject: Earthquake (61)
From: Genn Saji
I. Estimation of a release fraction using the DOE/NNEA land contamination data
With detailed land contamination density data now released from DOE/NNEA ( http://energy.gov/news/10194.htm ), as introduced in the attached figure “FukushimaDoseMap(May 6)”in Earthquake (60), it is straight forward to estimate the release fraction for the 1F1 release occurred on March 12 by a hydrogen explosion. The DOE/NNEA (May 6 update) results even include the land contamination density expressed in Bq/m2 for Cs-134+137, which can be used to estimate the total amount of the Cs just by computing the areas of each zone. However, the Bq/m2 results are shown with a bit coarse grouping for the first two high contamination density zones, I used the dose rate map instead, since contribution of I-131 gamma is almost negligible. In a linear build up factor approximation, D = Sa/2(exp(-z/lamda), well known from the days of Samuel Glasstone.
Zone Cs-total (Bq/m2) area (km2) Cs-134+137
V 6E+06 - 3E+07 151 4.53E+15
IV 3E+06 - 6E+06 116 7.00E+14
III 1E+06 - 3E+06 483 1.45E+15
II 6E+05 - 1E+06 379 3.80E+14
I 3E+05 - 6E+05 965 5.80E+14
Total 2094 7.64E+15
Since the shutdown inventory of Cs-134 + Ca-137 is 319 PBq for 1F1, the release fraction is <2.4%, by using the upper boundary values of Cs-total contamination density in the zone classification. Therefore the Fukushima Daiichi accident may have released a few percents of the shutdown core inventory of volatile species to the environment, it is not comparable to the releases from the Chernobyl accident. This values should not be confused as a fuel failure rate, since the containment system seems to have an order or so of decontamination factor. The actual fuel failure can be an order or so larger in the reactor vessel. These statistics indicate the following land contamination characteristics:
(1) The accident resulted in a severe land contamination (zone IV and V) in an area of 270 km2, where rehabilitation will be prohibitive without proving substantial amelioration to reduce the dose rate more than a factor of 10.
(2) It induced significant land contamination in a total area of 2100 km2, although most of the contaminated area is located in the Abukuma mountain chains.
(3) The public dose rates should be reduced as low as reasonably achievable for the region III and II as well, especially for activities by the children and pregnant women living in the contaminated region.
II. Recapping on risky situations in 1F3
TEPCO disclosed today that a worker found a water leak into the 1F3 pit, with a depth of 2.3 meters form the ground level, located near the Sea Water Intake Facility. The contact dose rate of the water was 1.5 mSv/h, which is much less that that at the basement of 1F3 turbine hall with 750 mSv/h. TEPCO observed the actual flow of water into the pit, although its water level is not changing. This indicate that the water is flowing out to somewhere. The leakage identified is again through a sleeve of cable penetrations, about 10 cm in diameter, making a 4x3 array. Since the pit was covered with debris, it escaped inspection. TEPCO immediately stopped the leak by plugging the sleeve by a special cloth and poured concrete. The operation was reported successful at 6:45 PM. There is a possibility that a portion of the leaked water may have escaped into the sea, since a bubbling surface was observed in the nearby sea. However, since the contamination level is lower than the 1F2 case, and duration may not have been long, the total amount of activity should be much smaller.
Well, let me stop here tonight!
(Previous e-mail sent at 10:41 PM on May 10 as Earthquake (60))
Today a home coming visit was arranged by the Government for the first group of evacuees from the “vigilance (off limit)” zone of 20 km from the Fukushima Daiichi, not including within 3 km zone. The first group members were selected from the residents of Kawauchi-mura, consisting of 92 people from 54 families. They gathered at a junction point, transported by a bus, where they wore radiation protection suits, each with a personal dosimeter and a transceiver for emergency communication. They are allowed to stay only two hours at their home and can take with me a garbage bag size of personal belongings. They were transported by five micro buses going to their convenient stops. Upon returning back to the junction point, they removed the suits and went through a dosimetory. Non of them need to be decontaminated, by receiving 1 - 10 microSv of radiation.
I. NSC made a press interview for usefulness of the land contamination map
Early this morning, the Nuclear Safety Commission acknowledged the usefullness of the contamination map now being made as a joint effort between MEXT and DOE/NNEA, by saying that the map is very helpful for planning how to ameliorate the highly contaminated areas. This is the time to re-arrange the land monitoring stations for improved objectives, Professor Madarame, Chairman of NSC, added.
The most recent data, updated on May 6, of the land contamination map is now available at
http://energy.gov/news/10194.htm. Using this data, let me update my primitive hand copy of the DOE results on top the SPEEDI map, originally provided in Earthquake (47) as attached. This time, DOE/NNEA kindly provided us in microSv/h unit, as well as classifying into 6 different zones. The new data motivated me to update my previous study, although primitive way, it helped me greatly to understand the contamination pattern, influenced much by wind directions and land scope effects. Some of the issues I noticed include:
(1) The distribution of the contamination density is in a reversed V shape, first going toward NW for about 50 km, then came to the SW direction, although the contamination density is much less than the first leg. The second leg seems to be due to a change in wind direction when the plume traveled about 50 km, along the so-called “Naka-Dori” district. This district is a valley district in between the Ohu mountain chains to the West and the Abukuma mountain chains to the East. The contamination is due to the hydrogen explosion of 1F1 on March 12.
(2) The contamination zone in the WS direction from the plant is likely due to venting of 1F1.
(3) Two additional streaks towards the S direction from the plant are likely due to explosion of 1F2 or other venting events.
II. Recapping on the accident scenario by referring to the SPEEDI results
On this issue, by Earthquake (58), I introduced a graphical representation of the monitoring data, displayed daily from March 12 to 15. Although a few large releases are recorded everyday, they are not directly correlated with the reported major events, such as initiation of containment venting, hydrogen explosion, etc. I was puzzled with the results.
However, one of my Japanese friends told me that METI has changed the time of venting from 1F1 on March 12. Following this, I updated my previous assessment as attached to be line with the METI announcement. The new data shows that the venting from 1F1 starting at 10:15 (instead of previous 14:30?). By making this correction, the venting at 10:15 matches the large increase in the dose rate around this time. However, there are several other large dose rate events that are not correlated well with the timing of the reported venting. It is likely there are other venting operations undisclosed yet. However, non of the hydrogen explosion events were caught by the environmental monitoring. This is very strange and I will continue to investigate this issue.
III. Recapping on 1F4 pool water video
A media report indicated that TEPCO started to reconsider the causes of explosion at 1F4 Spent Fuel Pool, since the video picture released recently on May 8 is showing no sign of overheating that may have induced hydrogen generation through zirconium-steam reaction. According to the media report, there are a lubrication oil storage tank for diesel generators (meaning “day tank”?), with a capacity of 100 tons as well as a propane gas bomb for welding in the reactor building, at the time of the accident.
If that is the only reason for TEPCO to dismiss a possibility of the hydrogen generation through water radiolysis, I have to point out that the Spent Fuel Handing Room located in the 4th floor is connected with the 3rd floor through ventilation ducts of the Reactor Building Reactor Room Heating and Ventilation System, which is a huge system serving the entire building. When this system is out, the room air can be easily flowed into other rooms by flowing through ducts.
Unlike the hydrogen explosion occurred in 1F1-3, the explosion in 1F4 has several unique characteristics;
(1) all the fuel assemblies have been evacuated into the pool, with no core inside of the reactor vessel,
(2) the explosion was not just limited on the 4th floor, but a portion of the structural wall in support of the pool load was also devastated.
Although I have been insisting that the root cause of the explosion is through abnormal accumulation-release of hydrogen through water radiolysis, I think this issue should be discussed in full. However, we should recall the pipe rupture accident induced by hydrogen explosion occurred on November 11, 2001 at Hamaoka Unit 1 of Chubu Electric Power Company. The accident occurred during a schedule test of High Pressure Steam Injection System, at a part of Residual Heat Removal System?pipe of 600 mm diameter. Although no in-depth study was made as to the root cause of hydrogen generation-accumulation mechanism as well as severe wall thinning mechanism observed in the pipe, this accident motivated me to look further into radiation chemistry and “macrocell” corrosion mechanism.
According to the video of 1F4 pool water situation ( http://video.mainichi.co.jp/viewvideo.jspx?Movie=48227968/48227968peevee388169.flv ), it is very interesting to see bubbles started to come out at this temperature of 80-90 degree-C. Although it is explained that the bubbles are steam bubbles, for me they are obviously hydrogen bubbles. The pool water seems to have been saturated with hydrogen gas generated through water radiolysis and started to release the excess hydrogen gas.
IV. A corrosion inhibiter in pool water
Since significant amount of sea water was injected into 1F3 and 4, amounting to 4556 and 721 tons individually, TEPCO added raw water containing a corrosion inhibitor, hydrazine, in the water poured in an amount of 80 for 1F3 and 100 tons for 1F4. TEPCO admitted that this is not an ultimate solution and they are also investigating a way to desalinate the pool water.
V. 1F3 pool video
Today TEPCO released video of the 1F3 pool, which was covered with a pile of concrete debris and not even possible to see the status of the spent fuels. http://www.tepco.co.jp/en/news/110311/index-e.html
VI. Risky situation continues in 1F3
I have introduced this issue on Earthquake (56). This troublesome issue persists, although very slowly. The remediation to provide more injection water was found not so simple, since the current route of water injection is going through many other systems, starting with the Fire Fighting System, en route of many auxiliary systems, including Condensate Supply system and Decay Heat Removal System? TEPCO decided to change the route to go through more direct Feed Water System. For that, it was necessary to first pump the highly contaminated water so far stored in the 1F3 turbine condenser back to the basement of the turbine hall. TEPCO is scheduled to do pipe work this afternoon.
In addition, the water level in the 1F3 increased to ミ73 cm from the ground level, and it already reached to a rule of thumb limit of -1m. It is increasingly urgent to transfer the highly contaminated water from the basement of the turbine hall as well as from the trench. TEPCO is also preparing to install a branch pipe for pumping the water to the Centralized Waste Treatment Facility. Previously, the priority was to pump the contaminated water from 1F1 trench, however, it is becoming urgent to use it for 1F3.
The temperature distribution is still unstable as shown in the attached update.
Well, let me stop here.
(Previous e-mail sent at 10:21 PM on May 9 as Earthquake (59))
I. Further recapping on a temporary ventilation system in 1F1.
Early this morning, 9 workers went inside of the 1F1 reactor building to measure dose rates for half an hour. During this operation, the maximum dose accumulated was 10.56 mSv, high but no health effect is anticipated, according to TEPCO.
The dose rate was as high as 700 mSv, although the area for workers to do some piping words at 2F was as high as several tens of mSv. At the region where worker activities are expected, the dose rate was as high as 40-100 mSv, although they hoped to reduce the dose rate to one mSv/h level by removing aerosols. TEPCO is planning to put temporary shielding, as well as removal of debris.
Prior to this the double door between the reactor building and the turbine hall was opened, No appreciable change in the area monitor, located near the West Gate, reading was identified.
II. Recapping on the release fraction using sea water sampling data
On this issue, I introduced an attempt to account for the release fraction, on Earthqukae (57), using a soil contamination data. Since a set of data taken from sea water samples near and off shore of the Fukushima plants was found available recently, let me try a similar assessment as attached, which is added to the assessment using the soil samples.
Although sketchy, it reveals some interesting release characteristics.
(1) Since the fission products from the fuel rods are first released into the reactor vessel, which are then transferred to the suppression pool water through the “feed and bleed” operation, the leakage from the containment vessel seems to have been decontaminated by the pool water. The highly contaminated water leakage to the ocean environment is likely a leakage of this pool water. This resulted in larger release fraction of Cs-89 and 90 than to the atmospheric environment, amounting to only 0.003 to 0.01 of Cs-137. This ration is an order of magnitude larger, indicating that a decontamination factor of the pool water is an order of 10. At the time of the Chernobyl accident, the fraction of Cs-89 was nearly the same as Cs-137, according to Table 2 of Annex J, UNSCEAR 2000 Volume 2. Fukushima Daiichi values are more than two orders of magnitude lower. Since Strontium is an “intermediate” species with high boiling point, the gross core melt is less likely at the time of releases. A fuel failure rate of several per cent appear to account for the damaged reactors.
(2) Since the release fraction of I-131 is not much different from Cs-137, these two radiation species are released, perhaps, not necessarily by making a compound CsI, since the release fraction is far from the stoichiometric ratio. If the release is through CsI only, the contamination density of these two species should be nearly equal, instead of in inventory ratio.
The ocean contamination through Sr-89 and 90 is a serious environmental concern, more serious than in the case of soil contamination.
III. Recapping on Prime Minister requested not to re-start Hamaoka NPPs.
The Chubu Electric Power Company decided to comply with the Prime Minister’s request to shutdown their fleet of 3 NPPs this evening. With out their NPPs, they will run into a situation with only 2-4 % in their excess power generation, assuming a normal temperature for the summer. In the case of a more than the normal summer, their power generating capacity will not meet the demand.
IV. A memo for lessons learned from the tsunami-induced nuclear disaster (continued)
For memory sake, let me add lessons learned.
(51) Environmental monitors at a high elevation location for severe accidents
Due to the station blackout, all of the environmental monitors went dead. This also included stack monitors. During the severe accidents, the effluent release may not be limited from the stack. TEPCO hurriedly provided a portable survey monitor and monitoring car for substitutes. In March 12, only two environment monitoring data were available. This situation was somewhat improved in the following days for the monitoring car running around the location near the dead environmental monitoring stations. However, the dose rate indications from these environmental monitoring alternative do not show any correlation with the major events related with the severe accident management procedure as explained yesterday in Earthquake (58).
Although the cause of this defect wait for further study, I noticed that there is no environmental monitoring provisions directly above the reactor buildings. During severe accidents releases are made with high temperature steam due to overheating or explosion. This hot release likely started climbing up to the sky due to the buoyancy force of hot steam, however, there was no environmental monitoring provisions available in this direction.
Perhaps a practical solution is to install environmental monitoring devises on the frame of the stack. The monitor should withstand 100 degree-C steam for several tens of seconds.
Well, let me stop here today.