Fukushima: day 105 & 106

Dear Colleagues:

106th day!

I. Recapping on the water purification system
Later last night, TEPCO made an announcement that the targeted DF of 100,000 was achieved, by combing the Kurion’s process and AREVA’s process, although the former system is still under the projected DF. They posted the results of sampling data of DF before and after the water treatment as below released on June 24:
Species Kurion’s process AREVA’s process Integrated
I-131 5.8 1.3 7.6
Cs-134 16 6700 1.1E+06
Cs-137 17 7200 1.2E+05
These results are strange, when compared with the sampling data released on June 22.
Species Kurion’s process AREVA’s process Integrated
I-131 7 1.1 7.8
Cs-134 41 >430 >2.0E+04 (limited by detection limit)
Cs-137 46 >480 >2.2E+04 (limited by detection limit)
TEPCO explained in June 23 that one bypass valve was inadvertently left open, feeding water from the top sorption vessel directly to the Ag-impregnated zeolite sorption line. By closing the valve, the DF decreased. The new sampling results seem to more pointing towards that the valve can be open as indicated by the hand-written marking, bypassing a portion of Skid 4. Also likely is the case that one of the cesium sorption skid has gone through “breakthrough.”
The most recent sampling results released June 25 are more discouraging:
Species Kurion’s process AREVA’s process Integrated
I-131 6.3 1.1 6.6
Cs-134 34 1800 6.3E+04
Cs-137 35 1800 6.3E+04
These results indicate that still further optimization, including finding better sober for SMZ tank. So far, 4500 tons of water has been purified.
The unexpected DF of 16-17 can also be due to replacing SMZ into silica gel in the front end, due to unexpectedly high dose rate only after 5 hours of operation. Silica gel does not have good DF for oil removal since it is not porous material. A more common porous mineral material is parlite, although it does not seem to be a very good sober for oil contamination. Therefore I recommended to try “needle coke” as a candidate for removing oil contamination at the front end.
In addition, the announced DF represents just three gamma emitting species and do not cover all the nuclear species likely be included in the highly contaminated water. Some of them with large core inventory and mobility into the contaminated water are summarized in the attachment (Activity_Concentration_100d.doc) It appears that both Kurion as well as AREVA tailored the system only for cesium, technetium and iodine. I presume other important species are just pass through the process. For this point of view, I believe the Kurion’s last stage using Ag-impregnated herschelite need to be improved for sober with wider absorption capabilities. Although there exists such a sober exist (e.g. LHT), unfortunately the DF becomes very low in sea water. Therefore, it may necessary to add one more stage after desalination, to remove other radionuclides.
TEPCO also release a sampling result of the desalination process, indicatinga DF of 265 for chloride.

II. Recapping on a temporary level gauge for the Reactor Pressure Vessel.
I introduced this issue in Earthquake (1003). Today, TEPCO released that the temporary level gauge is still not functioning pr0perly, due to dry out of the “condensing pot” which provides the reference level presssure.
A graph is released as attached. The reference point is decreasing consistently below zero, which is unreasonable.
(In Japanese, http://www.tepco.co.jp/nu/fukushima-np/images/handouts_110625_02-j.pdf )
The newly installed level gauge also provided that the current reactor pressure vessel pressure is 12 kPa, slightly above the atmospheric pressure.

Well, let me stop here tonight!

Genn Saji
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(Previous e-mail sent at 10:01 PM on June 24 as Earthquake (105))
Dear Colleagues:

105th day!

I. Recapping on the water purification system
Very early this morning, it was reported that TEPCO will continue the current campaign using the real highly contaminated water, even when an high dose rate alarm exceeding 4.7 mSv/h is reached. When it became necessary to replace sober, the entire system will be flashed with low level contaminated water to reduce the worker doses. It is said to take approximately two hours for the flashing. In parallel with this, their optimization study continues so that one critical sorption tank will not prematurely come to its life.
They also disclosed the operational results (bar charts), as attached, showing that the initial problems are in the front end SMZ sober, which is currently replaced into silica gel in place of zeolite. This is reasonable since zeolite tends to catch cesium, resulting in early breakthrough even with low DF. I made a quick e-mail search looking for better oil removal sober material and came to a conclusion that so called “needle cokes” could be tested, although it is going to be a headache for ultimate disposal, if the material also adsorbs cesium. The needle cokes is a hydrophobic porous material actually used for removal of oil contamination by weaving into mats by NIPPO corporation. (In Japanese, http://www.nippo-c.co.jp/ourbuiss/plant/products/kyutarou.html ) I came to this conclusion by reading a recent paper by Serbian scientists BRANISLAV R. SIMONOVI? et al., REMOVAL OF MINERAL OIL AND WASTEWATER POLLUTANTS USING HARD COAL, in Chemical Industry & Chemical Engineering Quarterly 15 (2) 57-62 (2009).
TEPCO’s bar-chart also indicates that the breakthrough time for a cesium sober tank is approximately 33 hours. For commissioning, how to accomplish the periodical it is necessary to optimize procedure of replacement of sober materials with minimum worker doses as well as with highest throughput.
I think current TEPCO’s approach is reasonable and practical, in view of current urgent situation of continuation of the volume of the highly contaminated water increase by 400 tons a day, even not including rain water from the roof-less reactor buildings. By looking at the more detailed schematics, I noticed that basically each skid has 3 sorption tank in the US Kurion’s system. These three tanks are connected in series, composing one tall sorption column equivalent. The radiation monitor at each tank should be a good indicator for telling that the “breakthrough” reaching to the bottom of that tank. When the dose rate increased to a high level at the last stage, it will be the time to stop operation for maintenance. It appears that TEPCO people began to learn the system specific characteristics. So the real issue will be the accumulated worker doses during the next maintenance campaign, which I anticipate will become necessary in another few days. The “breakthrough” in the front end “oil removal and technetium” removal tanks as well as the last stage “iodine removal” tanks will also be a critical if one of them reached “breakthrough” prematurely. Whether to stop under this situation or not should be discussed before hand. Because of urgency of continue operation of the water purification system, I am on the side to continue as long as the cesium sorption tanks are working.
In parallel with this, TEPCO announced today that they will initiate the pre-commission test of the final 4th stage for desalination. This test has been flow tested during the flow test using low contamination liquor. The new campaign uses 3000 tons of water already processed through the pre-commissioning test of the first stage for oil and technetium removal, the second stage for Kurion’s cesium and iodine removal, and the third stage for AREVA’s co-deposition process for cesium removal.
Later TEPCO made an announcement that the targeted DF of 100,000 was achieved, by combing the Kurion’s process and AREVA’s process, although the formersystem is still under the projected DF. Since the final contamination level of the treated water is below 100 Bq/cm3, the final desalination system can now be tested.

II. Recapping on the personal dosimeters for every school children in Fukushima
I introduced this topic in Earthquake (102). The Fukushima Prefecture decided to distribute personal dosimeters, to record accumulated doses by using “glass badges”, to every school children, totaling to 280,000 pupils. This operation will be accomplished by creating an Urgent Program for Protection of Young Children. Pregnant mothers, estimated 20,000, will also be included. The project also includes remediation of school ground, installation of air conditioners. The remediation of school ground have already been completed, reducing the dose rate as low as to 0.5 microSv/hr. Even with this low level, schools and parents are prudent to limit usage of the school grounds, without knowing how low is low enough.
In view of the parents’ concern against radiological safety, the national government decided to allocate budget to monitor radiatiological health effects of entire residents of Fukushima Prefecture for coming 30 years, by creating a special funding organization with an endowment of ten billion yen (approximately 120million US dollars). This was first spearheaded by the Fukushima Prefecture, but in view of the national government responsibility of supporting nuclear energy, the national government is to take up this initiative. By first reviewing questionnaires, the people which might have received high radiation will be screened. In some cases, their internal exposure will also be measured. This is to respond increased anxiety among the residents as to the effect of low level radiation for long term, which may accumulate defects in DNA. The government intends to ask TEPCO to share more than twenty percent of the endowment.

III. Recapping the water injection rate and current decay heat
I introduced this issue on Earthquake (99). At news interview, TEPCO released the current water injection rates
Unit Water Injection rate (ton/h) RPV Temp. (at the feed water nozzle) RPV Temp. (at the lower part)
1F1 3.6 118.7 102.8
1F2 3.5 108.5 110.1
1F3 9.0-9.1 151.1 121.9
The decreased flow rates indicate that the decay heat has further went down.

Well, let me stop here tonight!

Genn Saji