Update from Dr. Saji- former Secretariat of Japan's Nuclear Safety Commission
Date: Wed, 13 Apr 2011 20:42:05 +0900
Subject: Earthquake (33)
From: Genn Saji
I was so disappointed with the Government's unscientific decision of raising the INES severity assessment to Level 7 for Fukushima Daiichi yesterday, in spite of all of my effort to develop nuclear safety goals using this scale several years ago. I felt so tired to write this series of diary. After a good sleep last night, I am now refreshed to continue my evaporation and assessment of the accident as a scientist as well as a former nuclear engineer who has worked in several gigantic national and international nuclear development and construction projects. They include LMFBR Monju Project, Rokkasyo-mura Spent Fuel Reprocessing Plant Project, working closely with a French engineering company, SGN, and ITER/Fusion as a safety division head of the International Joint Central Team in San Diego for six years. My alma mater is the Nuclear Engineering Program, University of Illinois, Champaign-Urbana. Many of my former advisors are still there, although they are at their retirement age. I used to work as a teaching assistant/grader as well as a nuclear metallurgy lab instructor for several years at the university. So I have international friends everywhere in the world. I further broadened my international acquaintances through my recent private research interests concerning the radiological consequences from the Chernobyl accident as well as more recent studies on the scientific mechanism of corrosion degradation of aged plants, from high temperature electro- and radiation chemistry point of view. One of my motivation of start writing this series of diary is to keep my international friends informed with what's happening at Fukushima Daiichi.
I. Stop that leak?
For last two days, the frequent aftershocks prevented the urgent operation to transfer the highly contaminated water accumulated in the trench (tunnel) of 1F2 into its now empty turbine condenser. Fortunately, there was no damage no seismic impact induced by the relatively large aftershock occurred at 14:00 on April 12. After confirming the safety of the damaged plants, the planned operation of transferring the highly contaminated water finally initiated at around 7:30 PM on April 12. By noon this morning the level went down by 4 cm in the trench, 5 cm inside of the basement of the turbine hall. For the first step they plan to pump 700 m3 in 40 hours for trial operation for checking potential leakages.
Also, the nitrogen gas charging operation to the 1F1 continues, although there is a high possibility of leakages from the containment vessel, indicated by a flat pressure reading at 1.9 kg/cm2. By?? PM of April 12, a total of 3600 m3 of nitrogen gas has been charged. I support this operation, since it is very likely that the containment vessel should have accumulated a significant volume of hydrogen gas, keep coming out through water radiolysis.
One concerned issue is that a portion of the pool water has leaked, likely through sloshing, from 1F2, resulting in an unavailability of pool water temperature sensor induced by the aftershock occurred in April 11, although the spent fuels are kept in the submerged condition. I was shocked to know why such a large amount of pool water was lost. Damaged building structure blown up by the hydrogen explosion! The pool was surrounded by the walls of the Reactor Building, which should have put the overflowed water back into the pool. I think it is an important phenomena, in discussing the root case of the hydrogen explosion in 1F4, where no fuel was left in the reactor vessel.
Another significant incident yesterday was a fire at the Sampling Building located near the common sea water discharge port of 1F1-4. The workers happed to be nearby and distinguished the fire soon. The fire is likely induced through grounding short of batteries. After the tsunami, many destroyed auto initiated fire spontaneously, through failures of electrical insulation due to sea water.
Although no report is available, I am increasingly concerned with a potential leakage of underground water into the contaminated buildings. As a matter of fact, several days ago, approximately 1500 tons of underground water accumulated in the sub-drain pit of 1F5 and 6 are discharged into the sea. This much of water may have seeped into the sub-drain pit, if it has been identified as the ground water without significant amount of salt content. Since the ground level of 1F5 and 6 is a few meter higher than the OP+10 meter ground level of 1F1-4, it should be reasonable to suspect higher underground water leakage into the contaminated soils. If the underground water leaked into the contaminated buildings, it should result in an significant increase in the volume of the contaminated water waiting for processing. The TEPCO's operation of injecting water-glass into the soil near the trench of 1F2 is prudent.
II. Recap on the new evacuation criteria announced by the Government
As anticipated, the Chief Secretary of State Mr. Enamo's announcement, made on April 11, triggered a lot of hardship to the affected regions of the residents. The new policy is to introduce planned (and organized) evacuation of those communities where the accumulated dose is expected to reach 20 mSv/y. The total population of the affected community is estimated to be 115, 000 people, not including those already evacuated within the 20 km region. The name of the affected villages and towns are: Namie-machi (town), most of Kuzuo-mura (village), Minami-soma-shi (city), Iidate-mura (village) and Kawamata-cho (town).
Comparing with the dose map as disclosed by the US DOE/NNSE monitoring maps of the US Nuclear Security Administration
I am critical with this government announcement. The most heavily affected communities can be limited to a narrow strip of Namie-machi and Iidate-mura, and rest of the fringe areas can be simply asked to move to a bit further away form the heavily contaminated regions within the same community.
I suspect an motivation of the knowledgeable Japanese scientists to prefer the results of SPEEDI even when only the fringe areas are heavily contaminated as shown by the US DOE/NNSE monitoring maps. The results by SPEEDI are predicting much wider areas of the plume passage, by the nature of its dispersion calculation approach, when comparing those 1.19-2.17 mRem regions. In addition, their results were based on their calibration through just several temporary aerosol monitoring data, taken after March 20, according to the press release from the NSC. I am more in favor of the US DOE/NNSE monitoring maps, since it is representing actual mechanism of wet deposition of radio-active species from the plume.
That is an effect of small black rain. I recall the very detailed Cs-137 land contamination map displayed at the Chernobyl Center. On the map, the very sharp and narrow stripes were shown towards the Western direction, corresponding to the first plume passage. This image is in consistent with my study as published in
G. Saji, 2005. A Scoping Study on the Environmental Releases from the Chernobyl Accident (Part I): Fuel Particles, International Topical Meeting on Probabilistic Safety Analysis, PSA'05, 11-15 September 2005, Sir Francis Drake Hotel, San Francisco, California, USA.
The width of this streak can be estimated from the total thermal energy of the mushroom cloud. My estimation for the Chernobyl was
-2.4 km diameter semi-spherical cloud, drifting Westward at a speed of 10 m/sec
-Uplifting 5 m/sec for 100 sec before the start of rain
-Terminal velocity of 5 m/sec
This black rain induced the red forest not by radiation but by its temperature above 60 degrees-C, according to my field study with a Japanese pine tree. The dose distribution map shown in the US DOE/NNSE monitoring is in consistent with this. It is likely the higher dose region represent heavier rainfall, surrounded by a mist rain region of wider streak, which correspond to the 1.19-2.17 mRem regions.
A more detailed Cs-137 surface contamination map around this region is highly waited. The Japanese way of taking soil samples down to 5 cm deep is not practical under this kind of emergency situation. Just a contact dose measurement of wider area is sufficient.
I believe, how to prevent a total disluption of the affected communities by minimizing the evacuation should be more seriously considered. Very often, societal risks are higher than the actual radiation risks. I do not like their flat 20 mSv rule. The objectives of the radiological health can be almost equally achieved by introducing 20mSv for pregnant mothers and little children less than one year old. In addition, from now on, the radiation exposure is through whole body from Cs-137 deposited on the soil. It may not induce much higher risk to thyroid as in the case of I-131 for younger generation. Let them give a year or so for evacuation of the whole community, if really necessary, by asking pregnant ladies and little children move out form the highly contaminated region.
The Government also impose voluntary evacuation region for the 20-30 km as before, for those regions outside of the newly introduced planned (and organized) evacuation policy. It calls for those people with difficulties to stay away from this region, for residents with difficulties in an event of urgent evacuation, such as children and pregnant women, aged and sick people who need continued nursing care and hospitalized patients. The Government will request to close nurseries for little children, kindergartens, grade schools and high schools in this region. A high ranking officials mentioned that it is not possible to deny possibilities of necessary duration of evacuation as long as several years. Many local people are feeling unhappy by saying why from now with the area doses are gradually decreasing. This is quite understandable, since the area monitor readings should be detecting gamma rays from both I-131 and Cs-137. What is important for evacuation of extended period of time is gamma coming from Cs-137. In a matter of 3 months, gamma from I-131 will become negligible. The concentration of I-137 is approximately 13 times larger than Cs-137. Considering these, I cannot understand the policy of the accumulated dose of 20 mSv/y flat, although food restriction, especially from locally milked cows should be avoided for 3 months.
III. Recapping on Level 7 for Fukushima Daiichi
Some additional information was released from NSC as to the amount of releases. They estimated the released source through a reverse engineering of the SPEEDI results starting from the area monitoring dose rate data. In their estimation, by using the data obtained between March 11 to April 5, the release of I-131 and Cs-137 has accumulated to 100,000 TBq mark and exceeded the INES guideline of several tens of thousands TBq. Mr. Kenkichi Hirose explained that the total amount of radio-active materials rapidly rose during March 15 to 16, followed with a gradual increase until March 21. It is likely that the pressure suppression room located at the bottom of the containment vessel appears to be damaged in the morning of March 15. If that is the basis for assigning Level 7, I doubt his hypothesis, by recalling my estimation of the fuel damage fraction based on the trench water sampling data, introduced in Earthquake (31), indicating the damage fraction of around 20%. A similar assessment was reported in a news media, indicating 10%.
However, there is one report I could not understand as to by which pipe route the venting was actually performed. It is given in a verification report by The Yomiuri newspaper on what was happening at 01:30 of March 12, at the Official Residence of the Prime Minister. The report was saying that the Prime Minister himself as well as METI Minister ordered to release the REACTOR VESSEL pressure directly through the pressure regulating valve, whereas TEPCO was reporting that the pressure inside of the CONTAINMENT VESSEL reached to 1.5 times the design pressure. TEPCO tried to open a valve for venting, however, without the electric power, they could not manipulate the valve operation and struggling to open by hands. The Ministers became so mad that they ordered venting on the basis of the Law of Reactor Regulation of Nuclear and Non-nuclear Facilities at 6:50 of May 12. By early morning, the pressure inside exceeded twice the design pressure of the containment vessel. When the Prime Minister found that TEPCO has not started venting at 7:00 AM, he questioned why his order was not implemented. They responded that they will decide in an hour or so. This made the Prime Minister furious. TEPCO started venting on 10:17, and the hydrogen explosion occurred 5 hours later.
In these early days, I was also confused how to release REACTOR VESSEL pressure directly to the environment, by following the news releases. Later, by consulting with a PSAR, I concluded the overpressure of the containment vessel was released through some un-identified pipe route. The REACTOR VESSEL pressure was likely under control through automatic (spring action) pressure release and safety valves, directly into the suppression pool water from the Reactor Vessel. Anyway a through verification is indispensable as to how the venting was performed. Dr. Harada, by tracing back the area dosimetory data, the releases from 1F1 is almost negligible. It is more likely that the three big releases occurred on March 15, likely from 1F3, induced the largest environmental impact.
The international opinions are split, for example Greg Jaczko, chairman of the US Nuclear Regulatory Commission (NRC), seems to be in support of the decision by the Japanese Government, whereas Denis Flory, IAEA Deputy Director General and Head of Department of Nuclear Safety and Security was saying that the accidental situation at Fukushima is far below the Chernobyl accident. INES is not a scale to call emergency responses, he said. It is true that INES is a tool for better communication of nuclear safety and not a tool to encourage emergency actions.
IV. Decommissioning plans
TEPCO requested to jointly engage in the future decommissioning activities for Toshiba Co. and Hitachi Ltd. Both of them presented their plans on April 4, by working with major US engineering companies. Both of them were proposing very challenging planning, 11 years for Toshiba, 30 years for Hitachi, latter on the bases of 7 group companies’ experiences who have engaged in decommissioning of the TMI as well as the Chernobyl reactors.
TEPCO also plans to remove spent fuels from the pools of damaged reactors as soon as possible to facilitate the decommissioning operation, most likely to the dry casks. However, since the reactor buildings of 1F1, 3, 4 are destroyed by the hydrogen explosion, a new innovative ideas are being studied.
In addition to these quick actions by industries, I also hope to see an international research center organized at Fukusima, so that the lessons learned from this nuclear tragedy can be shared internationally. I recall the Chornobyl Center for Nuclear Safety, Radioactive Waste and Radioecology, at Slavich, Ukraine. Perhaps Fukushima Center for Nuclear Safety, Decommissioning, Waste Disposal, Radioecology and Rehabilitation, since there are so many things we have to learn from this accident. However, I have a rather pessimistic prospect for this to happen by watching the direction of the TEPCO as well as the Japanese Government seems to be aiming. This is one of my motivation compelling me to keep writing this diary.
V. Pool water sampling from 1F4
During the water injection operation using a high powered concrete pump into the 1F4, a beaker amount of sampling water was obtained from the pool water. TEPCO is planning to analyzed the water. Through a camera, it was confirmed that the spent fuels are kept in a submerged condition. The temperature of the pool water was 90 degrees. The dose rate was 84 mSv. There are two possibility to account for this high dose rate. One is due to some damage to the spent fuel nduced in the course of the accident, and the other is due to a decrease in the necessary shielding thickness above the top of the spent fuels. I will keep a close eye on the sampling data, since it is a crucial information to understand the root cause of the hydrogen explosion, which occurred with all of the fuel rods were stored in the spent fuel pool. The reactor vessel was empty.
Well, let me stop here,
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