Japan Earthquake: nuclear plants

Jim Lagerfeld

Thank you for the quick linking! Reading both articles, it is still not clear to me whether the installation of the gas management system allowed the measurement of the fission products, revealing a process which might have been already continuing for some time, or whether the xenon is a totally new development. Is it clearer to you?

rowmag

Looks like from the second article that the gas filtering and measurement system was only started on 10/28, and this was the first measurement result from that. So this may have been going on all along.

Could this provide a source term for those transient mini-spikes seen throughout the Kanto area when it is raining and the wind is coming from the power plant? (Still waiting to see an example of such a spike when the wind is not coming from Fukushima Daiichi.)

Bodge

It's always the one you least suspect!

So is number 2 the cause of the I-131 that is turning up across Japan again?

Xe-135 has a 9 hour half life, so this must be recent.

More evidence of the "impossible" [transient?] criticalities.

Has the corium solidified after precipitating highly dense substances to the bottom?

Or is the bulk of R2's fuel still in it's original configuration and the control rods are impeded?

Bodge

From another forum: RE. Hydrogen in R2's PCV

"The source of the hydrogen is presumably cooling water hydrolyzed by direct contact with the damaged fuel. Yet the reactor temperatures are now reading well below 100 degrees C. If the fuel had left the reactor vessel, the hydrogen would be found in the secondary containment, which does not appear to be the case afaik. If that is indeed true, it seems logical to infer that damaged fuel is still in the reactor vessel."

Hydrolysis or Radiolysis ?

Where is R2's core ?

tsutsuji

http://www.tepco.co.jp/nu/fukushima-...11102_01-j.pdf Press release with the quantities detected in the left column (detection levels in the right column). Iodine was below detection level. The tables at the bottom are the measurements of PVC gas samples of unit 2 on 10 August and unit 1 on 30 July provided as reference.

rowmag

Why no I-131 if Xe-133 and Xe-135 are there?
Remained dissolved in water with no release to air?

LabratSR

English is up now. http://www.tepco.co.jp/en/nu/fukushi...11102_01-e.pdf

LabratSR

TEPCO: New criticality seen at No.2 reactor
http://www3.nhk.or.jp/daily/english/02_24.html

Xenon suggests possible nuclear fission
http://www3.nhk.or.jp/daily/en​glish/02_13.html

Bandit127

From the plant status update:
http://www.tepco.co.jp/en/press/corp...1110203-e.html

Hiyodori

Poor translation. It should be something like, "since we can't rule out the possibility a fission reaction had occurred." Literally, "it is not possible to deny the possibility that a fission reaction had occurred."

The translation in their English .pdf makes it seem that they have confirmed fission, which they have not. At least at the time of their press release.

rmattila

Fission reaction does not necessarily imply criticality: since there is in any case spontaneous fission taking place, as well as neutrons emitted by Pu-240 present, it is the amount of Xe, rather than just the existence of it, that we should be interested in. It would be great, if someone could make a quick estimate of the fission rate required to produce the observed concentration in the containment, so that we could see if the concentration would be in line with the amount to be expected due to these non-criticality sources.

I am currently on the road and can't unfortunately contribute.

Rive

It was a gas sample. So it contains all the noble gases present, but contains iodine only up to its vapor pressure.

To make things even less balanced, the iodine is continuously washed down to the SC/basements by the cooling water, while the gases are more likely trapped in the PCV.

tsutsuji

http://www.asahi.com/national/jiji/JJT201111020002.html (2 November 9:36 AM) 240 kg of borated water was injected from 02:48 AM for about one hour.

http://www.asahi.com/national/jiji/JJT201111020089.html (2 November 7:06 PM) On 2 November, the NISA said that Tepco had made new gas measurements on the same day at noon, and the result was that the Xenon concentration was nearly the same as on 1 November. However, as the values are scantly above detection levels, a measurement error is possible, and Tepco asked the NISA to analyse whether the detected substances are Xenon or not. According to the NISA, the concentrations of Xe-133 and Xe-135 added together measured on 2 November were the same as on 1 November with about one 10,000th of a Becquerel per cubic centimetre.

[Does that mean that the borated water had no effect ?]

Rive

I really wonder why they think that one time injections will have any (long term) effect. Once the injection done, they are immediately washing it all through with freshwater

Once the Boron gone the recriticality (if there any) will resume. AFAIK to prevent recriticality they have to maintain a stable Boron level around the fissile material.

The measured levels are so close to the detection limits, that I would wait with further conclusions while new data arrives (preferably measured with different equipment/method).

tsutsuji

http://www.meti.go.jp/press/2011/11/...11102004-6.pdf Document distributed by NISA during the 2 November 02:00 PM press conference. Borated water 10 tons (boric acid 480 kg) were injected from 2:48 AM to 3:47 AM. Together with asking JAEA to make a detailed assessment of the present analysis, it is planned to perform substance analysis of charcoal filter(s) again today.

http://sankei.jp.msn.com/affairs/new...1230026-n1.htm (2 November 9:21 PM) During a 2 November night press conference, the NISA said that, as a result of an analysis done by Japan Atomic Energy Agency (JAEA), it is confirmed that the gasses are Xenon 133 and 135.

http://www.jiji.com/jc/c?g=soc_30&k=2011110200765 (2 November 10:10 PM) Tepco said in a 2 November night press conference that as a result of measuring unit 2's extracted gasses again on 2 November at noon, nearly the same Xenon concentration was detected. Based on JAEA's analysis, it is almost certain that Xenon was detected. The NISA's Yoshinori Moriyama said that "localized criticality cannot be ruled out" and that there is also a high probability that Xenon is produced by spontaneous fission of substances such as plutonium.

http://www.47news.jp/CN/201111/CN2011110201000498.html (2 November 10:10 PM) As the NISA announced on 2 November that JAEA's assessment confirmed the detection of Xenon, it became almost certain that nuclear fission had occurred. Small quantities of radioactive Xenon were also detected from the filters Tepco newly installed on the same day on unit 2's PCV gas purification system.

http://www.tepco.co.jp/nu/fukushima-...11102_05-j.pdf The last Tepco pdf, showing the results of the analysis performed on 28 October 03:24 PM (only Cs137 and Cs134 was detected), on 1 November 1:51 ~2:20 PM and on 2 November at 11:59 ~ 12:29 noon.

etudiant

With the fuel in a post accident jumble, is the reactor not simply in a situation where there is fission, but the neutron multiplication is too low for amplifying the fission rate? Presumably the reaction rate could be analyzed for clues as to the fuel geometry.
What is unclear at this point is what scale of fission is involved. One clue may be that the amount of xenon involved is producing 10**-5 bequerels/cc. Assuming a reactor volume of 1000 cubic meters, the xenon radiation load is about 10**4 bequerels at present. That would suggest a minute level of fission.
Separately, does anyone know what the effect is of boron on the water purification system?
I would think the ion exchange columns would not be affected, but what about the AREVA chemical process?

Astronuc

Concerns of fission at unit 2
http://www.world-nuclear-news.org/RS...2_0211111.html
02 November 2011
Even with criticality (k=1), at essentially zero power, there would be little activity. The concern would be that the system could have k > 1, in which case the system could pulse or spike.

Fission products could come from spontaneous fissions, and perhaps spontaneous fissions could produce sufficient neutrons to cause other fissions in the fissile inventory.

There is great uncertainty, particularly with regard to the core and state of fuel, other than the expectation that part of the core melted, or was otherwise severely damaged.