Category: review

We were forwarded Dr. Saji’s latest daily update (Dr. Saji is Ex-Secretariat of Nuclear Safety Commission, Japan). He is now retired, independent from any government or industry group.

The following web site may provide additional information on what is going on everyday.
http://jaif.or.jp/english/
http://www.tepco.co.jp/en/press/corp-com/release/ 

Date: Sat, 04 Jun 2011 00:06:34 +0900
Subject: Earthquake (83)

From: Genn Saji

Dear Colleagues: 

84th day!

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
1F2     24,600
1F3     28,100
1F4     22,900
Centralized Waste Treatment Facility 13,3300 (transferred mainly from 1F2)
13,3300
——————————————
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 plan 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.

Genn Saji
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(Previous e-mail sent at 11:43 PM on June 2 as Earthquake (83))
Dear Colleagues:

83rd day!

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:

http://www.tepco.co.jp/cc/press/betu03_j/images/030821b.pdf
http://www.tepco.co.jp/cc/press/betu03_j/images/030821c.pdf
http://www.tepco.co.jp/cc/press/betu03_j/images/030821d.pdf

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.

Genn Saji
_________________________________________________________________________________
(Previous e-mail sent at 10:21 PM on June 1 as Earthquake (82))
Dear Colleagues:

82nd day!

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.

Genn Saji