Update from Dr. Saji- former Secretariat of Japan's Nuclear Safety Commission
| These are personal communications forwarded to the scientific community and are posted here only to provide much needed information regarding what is happening on the ground. |
Dear Colleagues:
58th day!
I. Recapping on a temporary ventilation system in 1F1.
After successfully installing a temporary ventilation system two days ago, and observing the decrease in aerosol density, there is a growing hope that worker should be able to get inside of the Reactor Building to start plumbing work for installation of external air coolers for decay heat removal. At 8:08 PM, TEPCO opened the personnel double door between the reactor building and the turbine hall, while keeping the temporary tent room with the ventilation system working. After 8 more hours of filtering the air, they will remove the tent to have workers get inside the Reactor Building with full covered masks without using air breathing apparatus.
The removal of the tent may induce some effluent release to the environment, however, their safety assessment is said to be confirmed the safety.
A video of the installation of a temporary ventilation system can be observed in the following website: Click Here
Note that the radiation monitor is showing 0.2-0.3 mSv/h in the video.
II. 1F4 pool water video
TEPCO also released another video of 1F4 pool water situation. The pool water temperature is as high as 80 degree-C. VIDEO
It is very interesting to see bubbles started to come out at this temperature. 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.
III. Recapping on the accident scenario by referring to the SPEEDI results
On May 5, as Earthquake(55), I introduced the results of correlation of the major events with the results of SPEEDI calculation. I tried to check my assessment by trying to correlate the dose rate measurements made by a temporary environmental monitoring data release by TEPCO. Due to the station blackout, all of their environmental monitoring stations were dead during the early phase of the accident. TEPCO quickly put a portable survey meter at the front entrance, supplemented by data taken by a monitoring car. Unfortunately, available data are very limited in the first few days. TEPCO has been releasing these data every day.
Attached please find a graphical representation of these monitoring data, displayed daily from March 12 to 15. On the March 12, only two monitoring locations were available. The results were rather disappointing. 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 am puzzled with the results. There can be several reasons:
(1) The radiation monitors may not be catching the events since it may also depend on the wind direction.
(2) Spontaneous venting may have preceded before initiation of the manual venting.
(3) The hydrogen explosion shot the effluent up to the sky, without so much of releases ground level.
In spite of these mysterious results, I still think that the major release occurred with the hydrogen explosion, since explosion debris were highly contaminated.
IV. Recapping on remediation of the school ground
Following the surface soil removal method performed by Koriyama-shi to reduce the dose rate of some of the school grounds, Fukushima-shi today 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.
Well, let me stop here.
Genn Saji
