Japan Earthquake: Nuclear Plants at 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-np/images/handouts_111102_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]

http://www.tepco.co.jp/nu/fukushima-np/images/handouts_111102_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.

English is up now. http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111102_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:

On November 1, we conducted a nuclide analysis of emitted gas sampled by
the gas management system of the reactor containment vessel. It was found
out that there was a possibility that short-half-life radionuclide (xenon
133, 135) was detected. There has been no significant variation as a
result of our continuous monitoring of the temperature and the pressure
in the reactor, and the figures of the monitoring posts. However, just to
be safe we injected boric-acid solution through reactor water injection
line from 2:48 am to 3:47 am on November 2, since it was undeniable that
fission reaction had occurred.

http://www.tepco.co.jp/en/press/corp-com/release/11110203-e.html"

 

[Hiyodori]

From the plant status update:
...since it was undeniable that fission reaction had occurred.

http://www.tepco.co.jp/en/press/corp-com/release/11110203-e.html"

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]

http://www.tepco.co.jp/nu/fukushima-np/images/handouts_111102_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.

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]

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

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/2011/11/20111102004/20111102004-6.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/news/111102/dst11110221230026-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-np/images/handouts_111102_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]

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).

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_Concerns_of_fission_at_unit_2_0211111.html
02 November 2011

The possible detection of xenon at Fukushima Daiichi 2 has led to questions over ongoing fission, but detection is uncertain and a translation error may have exacerbated anxiety.

Temperatures and pressures at all the damaged reactors at Fukushima have been stable and declining for several months, and all are now far below the target temperature of 100ºC: units 1, 2 and 3 are at 59.4ºC, 76.3ºC and 71ºC respectively. Airborne radioactive emissions from the site have dropped to within normal operating limits.

. . . .

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.

 

[clancy688]

I believe there was some confusion over iodine spikes in the pits around Unit 2 over the last few months. Recriticality was often favored as the best explanation for that behavior, but the final conclusion was always that we simply can't know what's happening there.
It's just that I don't find those discussions any more...

 

[zapperzero]

I believe there was some confusion over iodine spikes in the pits around Unit 2 over the last few months. Recriticality was often favored as the best explanation for that behavior, but the final conclusion was always that we simply can't know what's happening there.
It's just that I don't find those discussions any more...

here's one:

https://www.physicsforums.com/showt...hlight=recriticality+iodine+water#post3488599

There is indeed much more talk about iodine in here and also in the contamination&consequences thread I believe. The search function has been reasonably good to me.

That being said, the issue of spikes in iodine (and, indeed, the issue of spikes from some radiation sensors) should perhaps be reconsidered in view of this new information.

 

[hbjon]

There could be pockets of fuel allowing the geometry to be favorable for criticallity. I'm thinking smaller masses of transuranic stuff can be very unpredictible. Has there ever been experiments of small quantities of transuranic isotopes mixing under the forces of radiolysis? I struggle with the idea of achieving cold shutdown in all that as the stuff works to unwind it's energy toward stability. We surely live in exciting times ladies and gentlemen!

 

[Bandit127]

There seems to be a good consensus that fission is occurring in Unit 2.

Do we think that:

1. Due to the probabalistic nature of neutron capture, fissions are happening on and off purely by chance in a solid part of the core that has K ~ 1. With long odds, these occurences will naturally clump together. (Like 3 busses arriving at once after a long wait).

2. Part of the core is still mobile (either from the action of water or that, despite the temperature data, part of it is still molten).

I think that if fissions are happening purely by chance in a solid core, Xenon would have been detected on and off for months.

 

[thebluestligh]

There could be pockets of fuel allowing the geometry to be favorable for criticallity. I'm thinking smaller masses of transuranic stuff can be very unpredictible. Has there ever been experiments of small quantities of transuranic isotopes mixing under the forces of radiolysis? I struggle with the idea of achieving cold shutdown in all that as the stuff works to unwind it's energy toward stability. We surely live in exciting times ladies and gentlemen!

Long time follower of this thread, first time posting, so let me open by thanking mods, admin, and Tsutsuji!

I also kept thoughts about the conditions of melted fuel and how it affects cold shutdown.

Obviously, dose modeling and other calculations in March were based off the fact that it was freshly loaded fuel in the reactors.

Maybe someone here has some insight to share...

What affect can the composition of isotopes in the fuel have on potential estimates for release and control of activity? I say this due to the fact that some of the Xenon might indicate more volatile composition than previously thought probable?

How do more volatile elements affect modeling?

After meltdown, how can current cooling methods be expected to prevent internal activity?

How would a more volatile composition effect current cooling methods/assessment?

Has any neutron data been released?

 

[zapperzero]

I think that if fissions are happening purely by chance in a solid core, Xenon would have been detected on and off for months.

This is the very first time that test results have been published. There is no timeline to follow.

 

[SteveElbows]

I'm just catching up with these reactor 2 developments.

Do we know why they decided to put the gas system into reactor 2 recently, is there something that made them want to check this reactor in particular?

I've long been fascinated by reactor 2, since I first learned that radioactive release estimates suggested reactor 2 was by far the biggest culprit, and that the estimates for percentage of certain substances entering the environment were of a much wider range than for the other reactors (approx 1%-6% versus 1% for the other reactors).

If we couple this with other things such as the dates of the neutron detections, the level of contamination in the basement & trench water for reactor 2, then its not so hard to see why I've more than half-expected this reactor to be the source of important new revelations in future. But this is a physics forum so I had to try and keep myself in check and not veer wildly into the realms of total speculation.

That did not stop me commenting on a slow & small but sustained rise in measured suppression chamber temperatures a while ago. But that trend ceased so I couldn't take the subject any further, and when very similar temperature rises were seen again more recently I did not bother to comment. Now I am left wondering if we can revisit this topic, can it give us any clues given what is now being said about possible fission at reactor 2?

 

[zapperzero]

Obviously, dose modeling and other calculations in March were based off the fact that it was freshly loaded fuel in the reactors.

Nope. The age of the fuel is known and was known from the start. If the fuel had been fresh, there would have been much smaller releases of volatile fission products.

Has any neutron data been released?

Apart from the detection of neutron beams by sensors at the site boundary in the first hours of the accident, no.

 

[SteveElbows]

Apart from the detection of neutron beams by sensors at the site boundary in the first hours of the accident, no.

First hours may be a misleading way to put it, since it was some days before such things were detected wasn't it? Around the time things started to get bad at reactor 2 if I recall, but we've often been distracted from this possibility by the possible 'red herring' of spent fuel pool at reactor 4. Or not, for its still quite hard to separate the effects of reactor 2 & reactor building 4 events on the environment around March 15th.

 

[zapperzero]

First hours may be a misleading way to put it, since it was some days before such things were detected wasn't it? Around the time things started to get bad at reactor 2 if I recall, but we've often been distracted from this possibility by the possible 'red herring' of spent fuel pool at reactor 4. Or not, for its still quite hard to separate the effects of reactor 2 & reactor building 4 events on the environment around March 15th.

Reported late, detected early on (and never afterwards).

 

[thebluestligh]

Nope. The age of the fuel is known and was known from the start. If the fuel had been fresh, there would have been much smaller releases of volatile fission products.Apart from the detection of neutron beams by sensors at the site boundary in the first hours of the accident, no.

Thanks Zapper, I agree fresh fuel would have been much smaller. But would have become more like end-of-cycle fuel through the meltdown and subsequent internal activity?

Was that taken into account for at any point? if so when?

Any thoughts on how to interpret http://www.nytimes.com/2011/11/03/w...ma-reactor-in-japan.html?_r=1&pagewanted=all" article?

... detailed measurements had not yet been taken at two other severely damaged reactors on the Fukushima site, but [TEPCO Spokesman] acknowledged the possibility of episodes of fission there too...
...Tokyo Electric does not deny the possibility that the fuel may have burrowed into the ground, but its officials say that “most” of the fuel likely remains within the reactor, albeit slumped at the bottom in a molten mass...
...an engineer formerly employed at TEPCO said that tiny fuel pellets could have been carried to different parts of the plant, like the spaces under the reactor during attempts to vent them in the early days. That would explain several cases of lethally high radiation readings found outside the reactor cores...

 

[SteveElbows]

Reported late, detected early on (and never afterwards).

I just wanted to be more specific about how early on. Checking the data again, the first time neutron stuff was detected is march 13th 5.30am, and on multiple further occasions that morning. Then again at various times between 9pm on march 14th and 1.40am march 15th.

The source I used is the following document, I cannot remember whether there were any subsequent updates/corrections to this data.

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110528e14.pdf

 

[Bodge]

Between November 1st and 2nd, Krypton-85 went from 3.6 x 10^-3 to 5.3 x 10^-1 becquerels per cm3 in Reactor 2's PCV gas.

Also, here is the data for R2's CAMS and pressure:

http://www.tepco.co.jp/nu/fukushima-np/f1/images/11110212_level_pr_data_2u-j.pdf

I would like to see a graph of all this data going back to March.

They say that 2 of the radiation sensors are damaged BTW, but we should expect to find some patterns when matched with the temperature readings here.

http://www.tepco.co.jp/nu/fukushima-np/f1/images/11110212_temp_data_2u-j.pdf

 

[SteveElbows]

http://www.tepco.co.jp/nu/fukushima-np/images/handouts_111102_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.

Be careful with reading too much into the 28 October reading, since the detection limits are said to be orders of magnitude higher for the October 28th test compared to the November ones.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_111102_04-e.pdf

 

[SteveElbows]

Between November 1st and 2nd, Krypton-85 went from 3.6 x 10^-3 to 5.3 x 10^-1 becquerels per cm3 in Reactor 2's PCV gas.

Also, here is the data for R2's CAMS and pressure:

http://www.tepco.co.jp/nu/fukushima-np/f1/images/11110212_level_pr_data_2u-j.pdf

I would like to see a graph of all this data going back to March.

They say that 2 of the radiation sensors are damaged BTW, but we should expect to find some patterns when matched with the temperature readings here.

http://www.tepco.co.jp/nu/fukushima-np/f1/images/11110212_temp_data_2u-j.pdf

You won't necessarily see patterns by looking at CAMs and temperature data together. I tried this in the past when I was looking at reactor 2 suppression chamber water temperature rises, and a few possibilities showed up in the data, enough to talk about here for a while but not enough to draw any safe conclusions.

Looking at most recent data, I don't see anything noteworthy. But go back a little bit further and the CAMS D/W B and S/C B readings had a spike on October 25th at 17:00.

http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/11103012_level_pr_data_2u-e.pdf

 

[SteveElbows]

And as for recent temperature data, I don't see anything interesting that correlates with the October 25th CAMS spike. The only thing I can spot at all from recent temperature data is a 0.8 degrees C rise in suppression chamber water temperatures between the 5am and 11am readings on October 28th.

http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/11103012_temp_data_2u-e.pdf

I'll be looking at a much wider date range when I get the chance, but its anything like what I saw a month or 2 ago then any patterns likely won't be much more dramatic than the stuff I've just mentioned. Unless we think we can draw conclusions from dodgy CAMs data and some upward and downward trends in suppression chamber water temperatures, which I would like to be able to do but I doubt the data is strong enough to build interesting theories upon.

 

[zapperzero]

I tried to work back from the activity. I came up with something in the region of tenths of a gram of Pu being enough to contaminate a 100 cubic metre volume with the detected quantity of Kr.

Could someone check if I'm in the right ballpark, at least? Cause if I am, we can't rule out spontaneous fission as a cause, I think.

Anyway, the conspicuous absence of Iodine is making my head hurt. It should be way more plentiful than Kr, no? Is it being kept in the water by chemistry, retained inside the (by now relatively cool) corium, or what?

EDIT: it's really late here, I'll ask a mod to delete if it turns out I'm delirious from lack of sleep.

LATER EDIT: wait, no. I forgot they flushed the piping with nitrogen prior to installing the stuff that enabled them to take these measurements in the first place.
http://www.4-traders.com/TOKYO-ELEC...clear-Power-Station-as-of-3-00-pm-O-13859684/

So yeah, who knows what the true concentration of Kr is.

 

[SteveElbows]

I've now looked at a much wider range of reactor 2 temperature & CAMS data. Aside from the things I already mentioned from late october, and a number of gradual increases in suppression chamber water temperature that I've gone on about before, nothing really leapt out at me. As far as I noticed the october 25th CAMS spike is the only time since the early days of the crisis that both a drywall and a suppression chamber CAMS data reading spiked in the same way at the same time. And the temperature reading described as 'RPV Supporting Skirt Upper Part' has fluctuated in a more noticeable fashion in recent days than it has tended to before, but we are still only talking about changes of less than 10 degrees C.

 

[dezzert]

This is the very first time that test results have been published. There is no timeline to follow.

They've only done one other gaseous sampling from the reactors, and also from R2, and the results from Aug 10 showed Xe-131m in much higher quantities. If these are the only noble gas test results, then its safe to say fission has been ongoing, yes?

What troubles me is that Tepco intends to only test for particulates for cold shutdown requirements. Wouldn't the US or France test for gases and tritium as well?

 

[zapperzero]

I have a question. How about sticking a bit of metal wire inside to measure neutron flux via activation? It's probably easier than a full-on borescope expedition? There must be instrumentation pipes that can be used, at least to reach the inside of the PCV. In fact, I think I remember reading somewhere that such "sensors" are part of the standard equipment.