Fukushima: day 101 & 102

Dear Colleagues:

102nd day!

I. Recapping on the water purification system
After concluding that the high dose rate near the the front end SMZ sorption line is due to the “unexpected” high dose rate of the water that needs to be treated, TEPCO resumed their test using the real highly contaminated water. However, the system tripped at 7:20, this time due to overloading a pump of the re-circulation flow line of the “coagulation and settling” tank, the line which dilute the chemicals for co-deposition process. TEPCO adjusted the flow rate and resume operation around noon today. This test will be continued for a few more days so that it can be commissioned within a few days.
To cope with this critical situation in the water purification system, TEPCO also initiated a series of tests to reduce the water injection rate by about 10% in each unit. Although it may not help much, it is prudent to revisit the necessary water injection rate, since I began to observe that there can be variation of decay heat after a few months since the reactor shutdown. Attached please find the decay heat of 1F1-4, computed from an empirical equation but following a part of the operational history before arrival of the tsunami. The results indicate that there are some differences starting around a few months after the reactor shutdown.

II. Personal dosimeters for every school children in Fukusima.
Today, at Kawamata-cho, a part of this city is located within the “scheduled (and organized)” evacuation zone, personal dosimeters were distributed to approximately 1500 school children. The dosimeters will be collected every 3 months for the coming one year assisted by the Kinki University. A similar dosimetry will also be done in City of Fukushima as well as Date-shi, were hot spots are identified. In these district, a city wide effort to construct contamination maps is under way.

III. Recapping on Iidate-mura, which is within “scheduled (and organized)” evacuation zone
Today the local municipal office of Iidate-mura finished their last day service, before evacuating to City of Fukushima, which is located 20 km west. The village has a population of 6200 people. Among them, 206 people either have not found refuges or refused to evacuate. Some of them are caring aged and sick member of the family. They worry that the evacuation will induce worsening their medical condition. To provide minimum level of municipal services, five staffs will remain at the local government office. Villagers organized patrol teams to assure security for 24 hours during their evacuation.
There are 550 workers commuting to 9 small business factories. They are advised not to go outside, by bringing sack lunch every day. The workers are provided with personal dosimeters, whose accumulated doses will be reported every month to the central government. The dose reading in one of these factory, Yamada Electronics Industry, is reported to be 0.3 – 0.7 microSv/h. Workers may accumulate a few to several mSv for the first year doses, which should be acceptable, as long as they were not living in the highly contaminated area at the time of plume passage.
However, in trying to reconstruct the thyroid doses around the Chernobyl reactor, I found it seldom exceeded a fraction of Gy by inhalation alone, unless with ingestion pathway through a food chainof fresh milk. Because of that no thyroid cancer case has been reported among adults. Young children are different. Radiation health risk of low level but long exposure is not well accounted for, in particular with accumulated doses of a few hundred mSv a year.

Well, let me stop here.


Genn Saji
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(Previous e-mail sent at 11:48 PM on June 20 as Earthquake (101))
Dear Colleagues:

101st day!

Last night, I forgot to crick the send button. Sorry for your possible inconvenience.

I. Recapping on the water purification system
Since yesterday, TEPCO started to experiment by changing the sorption materials. They found that even if the front end SMZ sorption line was changed into a material without having any sorption capabilities, the dose rate did not go below 11.5 mSv/h. This observation lead them to conclude that the activity of the feed liquor itself was un-anticipatedly high, resulting in the higher dose rate. They explained that an unexpected high dose rate is perhaps due to sludge and oil ingredients in the real highly contaminated water. They also mentioned that the dose rate of the sorption tower was high, even if the highly contaminated liquor was drained, indicating that a significant amount of cesium has been absorbed. They intend to optimize the flow rate and frequency of refreshing the sorption material so that they will be able to re-start within a few days. It is reported that the storage facilities are all nearly full and TEPCO started to investigate a possibility of using the tank yard being prepared for storage of low level waste.
I am still much concerned with their explanation, through the following “back of an envelope” calculation. Suppose we have an infinitely long pipe of 5 cm radius, un-shielded, located at 200cm distance from the surface, containing the highly radioactive liquor of 1000mSv/h contact dose rate, the dose rate will be 16mSv/h, obtained just by the solid angle reduction. The observed dose rate of 11.5 mSv can be due to pipe doses. I do not believe the planned optimization will be effective in solving this generic problem.

II. Recapping on the 1F4 Spent Fuel Pool situation
TEPCO has been puzzled with their balance of injected water into the 1F4 spent fuel pool. For example, after the hydrogen explosion occurred on Narch 15, the water injection was not available until March 20. During that time, a portion of the pool water could have been lost by boiling, losing the submerged state of the fuel assemblies, which must have induced overheating to the spent fuel. However, there was no such observation. Also, after the water injection was initiated, the level of the SFP and the amount of injected water did not match. Now a high dose rate is being observed at the 5th floor of the 1F4 SFP area. Today, TEPCO concluded that the discrepancy is due to a double gate doors, which separate the SFP from another pool on top of the pressure vessel (Reactor Well) and one more pool (DSP) for storage of large in-reactor components, such as shroud. The attached picture, although in Japanese, is self-explanatory. In order to reduce the dose rate for worker entry into this area, TEPCO is going to pour additional 1000m3 of water into the Reactor well/DSP pool to recover necessary shielding thickness.

III. Additional data for radiation chemistry calculation
One of my colleagues requested additional data, which include some data for reactor and general plant parameters, for radiation chemistry calculation. Since it appears that this kind of data is not readily available in English, I decided to translate a portion of Wikipedia, currently being developed to compile basic data for Fukushima Daiichi. Attached please find the first of the data relevant to his request.

Let me stop here tonight.


Genn Saji
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