Japan Earthquake: nuclear plants

rmattila

Is it really so? In my reference inventory, the alpha activity of Pu-238 is about 5 times larger than that of Pu-240, but its SF probability is so much lower (1,8e-9 vs. 5,5e-8) that the SF rate would actually seem to end up lower by a factor of 5 (9e6 vs. 5e7):


[nuclide] [Bq] [T12] [T12(s)] [SF T12] [SF t12(s)] [SF prob.] [nu] [SF rate] [SF neutron production]
Pu-238 5,00E+15 87,7a 2765707200 4,90E+10 1,55E+18 1,79E-09 2,2 8,95E+06 1,97E+07
Pu-240 9,00E+14 6550a 2,06561E+11 1,20E+11 3,78E+18 5,46E-08 2,2 4,91E+07 1,08E+08
Cm-242 3,00E+16 162,8d 14065920 7,20E+06 2,27E+14 6,19E-08 3 1,86E+09 5,58E+09
Cm-244 4,00E+15 18,11a 571116960 1,40E+07 4,42E+14 1,29E-06 2,8 5,17E+09 1,45E+10

Even though the conclusion is the same, it would be nice to know where and why our results differ in this respect.

tsutsuji

http://www.meti.go.jp/press/2011/11/...11104007-2.pdf Report from Tepco to NISA about the xenon detection. (4 November 2011, Japanese, 18 pages)

thebluestligh

Thanks Tsutsuji as always, I found a report from TEPCO in English version as well

http://www.tepco.co.jp/en/press/corp.../111104e19.pdf

rmattila

If I understood the TEPCO report correctly, they have

(a) completely neglected the subcritical multiplication, justifying this by conservativity
(b) assumed all Xe-135 created by SF is immediately released in the containment airspace, which I think is a huge error in the non-conservative direction, since the cool fuel/corium should certainly be able to contain a significant amount of the fission products

Did I miss something? Can someone make better sense of the report?

zapperzero

I'm more interested in why they keep harping on about Curium. It's certainly not the only fissile in there.

To your first question: it is strange indeed.
As to your second question, they are probably assuming that the corium is saturated, so naturally all excess production goes into the containment immediately.

tsutsuji

Thanks for the English version.

The following translation, while not wrong, was forgetting to mention that the ratio is found using the krypton 85 measurements:

dezzert

The following is from
http://www.tepco.co.jp/en/press/corp.../111104e19.pdf

If the Unit 2 fuel is in the critical state, Xe135 concentration is observed 4 orders of magnitude larger than current level. Therefore, present state is not considered critical.

OK, so on Aug 9 they found Xe-131m at 3.8 X 10¹ to 4.7 X 10¹ Bq/cm3 in the lower floors of Unit 2. This is 5 orders of magnitude greater. According to Tepco's analysis criticality has occurred. Am I missing something?

rmattila

The contribution of the residual I-131 (remaining in the containment water since March) on the Xe-131m production.

clancy688

Via EX-SKF:

Comparison between the three gas tests on October 28th, November 1st and November 2nd. Looks quite funny. With the detection limits being very funny.



So... what the heck? No wonder they didn't detect any Xenon on October 28th.

dezzert

Thanks rmattila. Woudlnt the residual I-131 be gone by then. And certainly not in numbers to produce those levels of Xe-131m.

NUCENG

I am using a different source term list from a US BWR4 and the fission branch percentage and isotopic yields I used from an old textbook. The textbook data includes data uncertainty ranges which I used to produce conservative (low) results. I used the same source term and updated values for fission branch and yield from http://atom.kaeri.re.kr/index.html and now Pu-240 is about 4 times larger than Pu-238. Since the data I got online has no uncertainty data I classify the new results as a best estimate case.

My analysis included 4 Uranium isotopes, 1 neptunium isotope, 6 Plutonium isotpes, 3 americium isotopes, and 5 curium isotopes that can spontaneous fission. All of my results are well within one order of magnitude of yours which is what I believe is reasonable agreement based on different data and the uncertainty of that data. Switching to the new values did not change that result, because the effects of curium seem to control the data.

Other than that I made several assumptions and some additional data:

• I developed and solved a linear first order differential equation based on fission and spontaneous fission sources and removal by decay and leakage. It demonstrated that the isotopes of concern are appropriately treated as equilibrium values due to the long half lives of the fission sources.
• I assumed that the relative sources for spontaneous fission
• My inventory lists 50 transuranic and actinide isotopes and is based on a typical equilibrium core. Japanese operating cycles are probably shorter and so transuranic sources may be overestimated.
• I assumed a single fission product yield curve for U-235.
• I assumed a single value for neutron yield from fission.
• I assumed zero out-eakage, but ran cases for 5, 10, and 20% keakage rates.
• I included cases for Keff and subcritical multiplication from 0.7 t0 0.999. I used the results for Keff -0.8 for consistency.
• I included release of Xe from I Beta decay.
• I used a smaller free voulme for containment to account for a water level inside containment.
• I uswd source terms based on 8 months decay and buildup.

rmattila

I did not have a suitable BWR inventory right at hand and no time to calculate one either, so I had to do with a VVER EOC inventory and scale it according to the thermal power level. Using an EOC inventory, I probably overestimated the transuranics, thus I believe your results to be better than the quick sketch I made in order to have at least something to base the estimates on.

NUCENG

clancy 688 - what are the units of those measurements? dezzerts values (Bq/cm^3) from Unit 2 are significantly different.

clancy688

Sorry, but what do you mean?

All of these values have the unit of Bq/cm³. Here's the original.

LabratSR

New results from Unit 2 containment released. Using different filters. Released Nov. 4, sampling date Nov. 1

http://www.tepco.co.jp/en/nu/fukushi...11104_04-e.pdf


Sampling System
http://www.tepco.co.jp/en/nu/fukushi...11104_03-e.pdf

zapperzero

And there's my answer. Thank you.

dezzert

And this is the original that showed both Aug 9 readings (reported on the 10th) as well as Nov 1. Lower left box is Aug. Why they only tested for Xe-131m and not 133 or 135 is a mystery.
http://www.tepco.co.jp/nu/fukushima-...11102_01-j.pdf