Fukushima: day 103 & 104

Dear Colleagues:

104th day!

I. Recapping on the water purification system
TEPCO seems to be puzzled with an unexpected rise in dose rate in the sorption tanks in the down streams. They were anticipating that most of the cesium is going to be absorbed in the up stream tanks. Before starting the test using the real liquor, the dose rate of the down stream tanks were 3 mSv/h, which jumped to 15 mSv/h. TEPCO now suspects that there should be some flow distribution anomaly in the process.
This morning, TEPCO made a press release by showing a bit more detailed schematics as attached
( in Japanese, http://www.tepco.co.jp/nu/fukushima-np/images/handouts_110623_01-j.pdf )
and explained that one bypass valve was inadvertently left open, feeding water from the top sorption vessel directly to the Ag-impregnated zeolite sorption line. The schematics is showing that there are 4 parallel molecular sieve sorption skids. Each skids contains 4 sorption tower in series. Their announcement indicates that the top vessel of Skid 4 has already completed its life through “break though” in just one day. In another few days, an entire replacement of the sober, as many as 20, is going to be necessary. Whether such maintenance can be performed without remote maintenance is my persistent concern.

Well, let me stop here tonight! The news about Fukushima Daiichi were very limited today, by some unknown reason.

Genn Saji

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(Previous e-mail sent at 10:11 PM on June 20 as Earthquake (103))
Dear Colleagues:

103rd day!

I. Recapping on the water purification system
Since this is the most urgent issue, I have to start with this topic.
After readjusting the flow rate of the “coagulation and settling” tank in the AREVA’s system, TEPCO resumed pre-service operation at around 12:30 PM yesterday and kept running until 10:00 AM today, June 22, for replacement of, perhaps, sober from tanks. During this campaign, as much as 1800 tons of highly contaminated water has been purified by extracting water from the Centralized Waste Treatment Facility, whose water level dropped down by 40 cm.
Since some room has now became available, TEPCO started to transfer similar highly contaminated water from the basement of the 1F3 turbine hall. This operation resulted in terminating the consistent increase in the water level in the pit, which has reached only 12 cm from the ground level. The situation continued to be critical, since the Fukushima district now went into a rainy season yesterday. During June 23-24, a heavy rainfall is forecasted in Fukushima. The rainwater may accumulate in the roof-less reactor buildings, further increasing the total volume of the highly contaminated water estimated as much as 110,000 tons total.
However, the most recent data released tonight as attached showed DF of only 46 for both Cs-137 and Cs-134 and 7 for I-131 in the Kurion’s molecular sieve sorption stage, although DF was approximately 3000 when using the low level liquor. In the AREVA’s co-deposition stage, DF was better than around 500 for cesium, the upper boundary was limited by the detection limit. This phenomena is well known in chemical engineering called “breakthrough” in column dynamics, where the sorption reaction starts from the top surface, gradually going deeper until the original liquor just pass through without being absorbed. Obviously, the sorption column was used too long a time. I made a quick internet search and found the following website. http://www.separationprocesses.com/Adsorption/AD_Chp02c.htm The US Kurion may have a breakthrough curve for their molecular sieve sober, if not TEPCO should do a quick experiment by detecting the breakthrough by putting a dose monitoring system at the outlet of the sorption column. The 4 mSv dose alarm may have indicated the occurrence of breakthrough. If it occurred in just 5 hours, the sorption process will not work for this kind of highly contaminated water. As long as the final concentration of the water at the outlet of the AREVA’s system is ND, just resume the operation by skipping the Kurion process.
In order to reduce the volume of the highly contaminated water, TEPCO reduced the water injection rates to 4.5 m3/h for 1F1 and 2, 10 m3 for 1F3. Since the response of 1F1 and 1F2 are slight, they further reduced to 4.0 m3/h. However, in 1F3, the flow rate reduction of just 1 m3/h immediately resulted in a temperature increase of 4 degreeC at the water supply nozzle location to 149 degreeC and 7 degreeC at the bottom part to 138 degreeC. TEPCO continue monitoring the trends of these plants. The behavior of 1F3 is different from 1F1 and 2, perhaps indicating a difference in the core status or damage in the primary coolant boundary. In addition, the amount of the flow injection rate is several times more than necessary to remove decay heat, indicating a gross leakage.
I am continued to be concerned with the doses received by the workers for replacement of sober of the the front end SMZ sorption line. As I estimated, the sober needs to be renewed manually every day, not just once a month TEPCO seems to have been projecting. Whether this kind of high dose work can be continued is a big question. At least some temporary shielding should be applied, especially in the pipes running near workers.
Another recommendation is optimization of activation level of water in the the Centralized Waste Treatment Facility during the transfer process. In my understanding, the activation level of the 1F2 turbine hall water is an order of magnitude higher. This should be diluted with lower activated water from other buildings.

II. Dose maps and observation of highly contaminated water in 1F2
TEPCO released the dose measurement results as well as some pictures taken inside of the 1F2 Reactor Building by their 7 staffs and 3 industry supporting engineers on June 21 for just ten minutes. The planned dose accumulation was 6 mSv, whereas the actual doses ranged from 2.16-5.52 mSv. The results are shown in the attached following hand out in Japanese.
http://www.tepco.co.jp/nu/fukushima-np/images/handouts_110622_01-j.pdf
Please note a picture taken at SE corridor, where the dose rate is as high as 388 mSv/h, showing a dark brownish color in the water. Although some Japanese media report that it is an evidence of water contamination by corium, I do not believe it. The color looks like showing heavy contamination with hematite (Fe2O3). In BWR, it used to have heavy deposits of hematite on the surface of fuels, due to an cathodic potential induced by radiation, however, the hematite crud deposition was said to have been much reduced in recent years by introducing better water treatment systems (total desalination) in the primary water. Where this much of hematite has been deposited and was released to the highly contaminated water is a good scientific question. This situation is much different from 1F1 and 1F3, whose water color was more slight yellowish. I guess it is likely came from the re-circulation lines, where IGSCC has been reported many times in BWRs of this generation. This may indicate a location of crack in the primary coolant boundary.
Also, in 1F2, TEPCO plans to install a temporary level gauge for the Reactor Pressure Vessel.
http://www.tepco.co.jp/nu/fukushima-np/images/handouts_110622_02-j.pdf
TEPCO seems to admit that the instrumentation using Bourdon gauge type went out after “internal hydrogen explosion” I have been suggesting in the light of the Hamaoka Unit 1 hydrogen explosion/pipe rupture accident. This will affect pressure gauges, level gauges as well as flow gauges.

Well, let me stop here tonight!

Genn Saji