- #11,586
Shinjukusam
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Latest update from NHK says TEPCO retracts claim of criticality, states that the Xenon level is consistent with spontaneous fissioning of curium-242 and -244.
Shinjukusam said:Latest update from NHK says TEPCO retracts claim of criticality, states that the Xenon level is consistent with spontaneous fissioning of curium-242 and -244.
rmattila said:Attached is my rough sketch to estimate the amount of Xe-135 to be expected as a consequence of spontaneous fission in Pu-240, Cm-242 & Cm-244. I made it really quickly and have not been able to double-check my figures, so if you see errors, please point them out.
Some conclusions:
- The main SF contributor indeed seems to be Cm-244.
- However, the majority of fissions occurs in U-235 due to subcritical multiplication - at a rate highly dependent on the assumed multiplication factor.
- Thus boron should have an effet on the Xe-135 concentration even though it would be due to subcritical multiplication.
- The main uncertainty lies in the release fraction of Xe-135 from the fuel/corium. The measurement data given by TEPCO conincides with release fractions between 0,001 .. 0,01 % in my sketch - a plausible figure assuming the fuel (in whatever state it is) is cool.
- Effect of nitrogen injection in the containment was neglected in my sketch - however, its effect is smaller than one decade, and thus smaller than the uncertainty in the Xe-135 release fraction.
All in all, it appears that the measured Xe-135 concentration would be well in line with the figures to be expected due to spontaneous fission, and no criticality is needed to explain them.
Unit 2
11/3 12:40 In order to improve reliability of nitrogen injection, additional flow gauge is started to install at the Unit 2 nitrogen injection line.
Around 14:00 The work was finished. Although nitrogen injection was stopped for approx. 10 minutes during the work, there were no significant changes in the parameters
11/3 16:50 Since some increase at the hydrogen density (hydrogen density of 2.9% [As of 16:30 on 11/3]) in the exhaust gas from PCV was observed from the last time of nitrogen injection amount change (hydrogen density of 2.7% [As of 18:10 on 10/30]), nitrogen injection amount was changed from 21m3/h to 26m3/h.
NUCENG said:Questions have been asked by several posters about why radioiodine has not been measured in the gas samples. This may mean that the pH of the water in the containment and vessel have remained alkaline and is keeping the iodine in solution until it decays. Acidic pH allows radioiodine to release as iodine gas. Thus only the iodine generated by beta decay in of Xenon in the containment atmosphere would be available in samples. Calculating the equilibrium iodine concentrations from that source will provide an answer if it is less than the detection threshold.
SteveElbows said:Todays status update has info about a further rise in hydrogen density, and measures taken.
Unit 2
11/3 12:40 In order to improve reliability of nitrogen injection, additional flow gauge is started to install at the Unit 2 nitrogen injection line.
Around 14:00 The work was finished. Although nitrogen injection was stopped for approx. 10 minutes during the work, there were no significant changes in the parameters
11/3 16:50 Since some increase at the hydrogen density (hydrogen density of 2.9% [As of 16:30 on 11/3]) in the exhaust gas from PCV was observed from the last time of nitrogen injection amount change (hydrogen density of 2.7% [As of 18:10 on 10/30]), nitrogen injection amount was changed from 21m3/h to 26m3/h.
Taken from http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111103_02-e.pdf
Regarding the hydrogen concentration in the gas emission of the gas management system of the reactor containment vessel in Unit 2, we confirmed that it increased to approx. 2.3vol% at 5:00pm on 29 October, which was approx. 1vol% at the beginning of the operation. Therefore we adjusted the amount of injecting nitrogen gas from approx.14 m3/h to 16.5 m3/h in order to avoid exceeding the combustible threshold concentration (4vol%).
http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111030_01-e.pdf
tsutsuji said:I don't remember if the following 30 October pdf was already mentioned in this forum :
http://www.asahi.com/national/update/1030/TKY201110300269.html (30 October) says that 1% is the value on 28 October. It quotes a Tepco official, Susumu Kawamata, giving some kind of explanation but I don't really understand : "Didn't hydrogen leak out because an air flow occurred ?".
rowmag said:Thank you, NUCENG. That makes sense.
My other question was whether the krypton and xenon could possibly account for the occasional synchronized transient spikes seen around Kanto. The spikes are pretty small, around 0.05 uSv/h above steady-state levels, but the krypton and xenon concentrations measured here look so darn low (barely above detectable limits even when sniffing gas directly from inside the reactor) that it seems hard to believe they could be responsible for measurable signals a couple hundred kilometers away. Unless somehow even very low levels of these isotopes can trick detectors calibrated for cesium into reporting much higher values somehow? (I.e., if this gas were wafted past a GM counter, what kind of reading would that counter report?)
Otherwise, maybe the radon-daughters-kicked-up-from-the-soil-by-rain theory is the correct one?
NUCENG said:Only minor difference is that I believe Pu-238 is actually a larger source than Pu-240, but two orders of magnitude less than the Cm isotopes.
tsutsuji said:http://www.meti.go.jp/press/2011/11/20111104007/20111104007-2.pdf Report from Tepco to NISA about the xenon detection. (4 November 2011, Japanese, 18 pages)
thebluestligh said:Thanks Tsutsuji as always, I found a report from TEPCO in English version as well
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/111104e19.pdf
rmattila said: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?
thebluestligh said:Thanks Tsutsuji as always, I found a report from TEPCO in English version as well
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/111104e19.pdf
Collection efficiency of the charcoal filter is 1566 times as determined from the ratio of the values of Kr-85 measured in the charcoal (5.3E-1 Bq/cc) and [STRIKE]the value measured[/STRIKE] in a vial (8.3E2 Bq/cc).
dezzert said:Am I missing something?
rmattila said:The contribution of the residual I-131 (remaining in the containment water since March) on the Xe-131m production.
rmattila said: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.
dezzert said:The following is from
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/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?
clancy688 said:Via http://ex-skf.blogspot.com/2011/11/xenon-detection-in-reactor-2-different.html" :
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.
NUCENG said:clancy 688 - what are the units of those measurements? dezzerts values (Bq/cm^3) from Unit 2 are significantly different.
NUCENG said:the effects of curium seem to control the data.
clancy688 said:All of these values have the unit of Bq/cm³. http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111102_04-e.pdf" the original.
tsutsuji said:TBS video showing a robot performing debris removal on unit 3's first floor under radiations up to 650 mSv/hour.