Fukushima: 96 & 97 days

Dear Colleagues:

97th day!

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:
March 11
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)
March 12
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 –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,

Genn Saji
__________________________________________________________________________________
(Previous e-mail sent at 10:11 PM on June 15 as Earthquake (96))
Dear Colleagues:

96th day!

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!

Genn Saji