Japan Earthquake: nuclear plants

  • Thread starter gmax137
  • Start date
1,045
2
The obvious answer to the I-131/Xe-131m question is ongoing transient criticalities.

Is there enough pu-240 for significant spontaneous fission?

Can we trust the decay heat calculations, which are based on all fission stopping at SCRAM?
Wikipedia gives 26% Pu-240 (from total Pu inventory) in spent fuel.

There are some temp spikes iirc in the graphs from the first few days and I don't really buy the "faulty sensors" explanation, because now the sensors seem to be doing just fine, tracking the water injection rates in a most satisfactory manner.

The question could be settled quite easily. But I have this sneaking feeling that TEPCO isn't checking for neutrons, 'cause they don't want to know.
 
144
0
Can anyone debunk the obvious conclusion that fission is ongoing ?
 
299
1
Can we trust the decay heat calculations, which are based on all fission stopping at SCRAM?
I think that those calculation arent apply in this case, they are for normal reactor, not melted corium... We dont know where corium is now so we cant trust any sensors, for example temperature sensors will show correct values only when core is where it should be, but if corium is in basement then temp sensors will show lower readings... This is sad but we still dont know much about real situation inside reactors...
 
244
1
It is very difficult to make any conclusions on the I-131 concentrations detected in different places, since the chemistry of iodine in the aqueous solutions found in different places of the Fukushima Dai-ichi complex is somewhat complicated. The pH of the containment water is affected by the materials from the instrumentation cables and the boric acid added to the injected water at at least some occasions, and then there's the salt etc.

It looks strange to see the levels of iodine with respect to Cs dropping slower than their decay ratio would suggest, but Cs tends to stick to surfaces, and there can well be chemical mechanisms that contribute to iodine migrating more rapidly. There's still plenty of I-131 left 5 months after the scram, even though it has halved every 8 days.

If you want to find signs of criticality, I think you would be better off finding anomalies in the ratios of short-to long lived nuclides of the same element (I, Cs) to be able to eliminate the effect of the chemical complications. However, it seems that the concentration of most radioactive isotopes is below the limit TEPCO is capable of detecting.
 
Last edited:

etudiant

Gold Member
1,186
110
It is very difficult to make any conclusions on the I-131 concentrations detected in different places, since the chemistry of iodine in the aqueous solutions found in different places of the Fukushima Dai-ichi complex is somewhat complicated. The pH of the containment water is affected by the materials from the instrumentation cables and the boric acid added to the injected water at at least some occasions, and then there's the salt etc.

It looks strange to see the levels of iodine with respect to Cs dropping slower than their decay ratio would suggest, but Cs tends to stick to surfaces, and there can well be chemical mechanisms that contribute to iodine migrating more rapidly. There's still plenty of I-131 left 5 months after the scram, even though it has halved every 8 days.

If you want to find signs of criticality, I think you would be better off finding anomalies in the ratios of short-to long lived nuclides of the same element (I, Cs) to be able to eliminate the effect of the chemical complications. However, it seems that the concentration of most radioactive isotopes is below the limit TEPCO is capable of detecting.
Hi rmattila,
Thank you for your cogent and insightful comments.
Between the minimalist disclosures from TEPCO and the 'sky is falling' summaries from eNews, you provide a refreshing and factual input. Would that many others would learn from your example.
Please keep participating.
 
144
0
So, left over I-131 from 11th March is responsible for the levels in the sea outside Reactor 2 and the Xe-131m in the air in Reactor 2's containment?

I-131 was found at the same concentrations on July 5 and August 10th - 4 half lives later.

You are saying that the I-131 produced by fission up until 11th March is responsible for the 90 beq/litre found in the sea outside R2 now.

20 half lives have passed.

I think something is 'fizzling'
 
190
15
Last edited by a moderator:
So unit 2 has I-131 in water and Xe-131 in air (containment) as late as August.
Radiation spiked in Tokyo, Kanagawa and Saitama yesterday. The obvious explanation is weather related - we had rain from the north for the first time in quite a while. However I'm not sure if the size of the spike quite tallies with the governments statement that emissions are "80% lower than July" and "one-10 millionth the levels in mid-March" (source - http://www3.nhk.or.jp/daily/english/17_30.html [Broken]).

I posted a link to a screen capture of the graphs in the environmental consequences thread but if you don't mind I'll drop a link here too. I was standing on a film set in Kawasaki city yesterday (red line) so I can confirm the spike coincides perfectly with a heavy rain storm which came in from the north and broke about 11.45am : http://i51.tinypic.com/vrr81x.png
 
Last edited by a moderator:
144
0
Last edited by a moderator:

NUCENG

Science Advisor
914
0
According to Bloomberg's original news the monitoring post was set to go off at high levels of radiation. But I guess if there would have been high levels of radiation 1.5 km from the no. 1 reactor also some other monitoring posts would have been triggered?

Surely this cannot be the only monitoring post at the Fukushima plant, can it?

http://www.bloomberg.com/news/2011-05-19/fukushima-may-have-leaked-radiation-before-quake.html [Broken]



Why has TEPCO not given us any more information about this monitoring post? Or have they?

The next information about possible radiation comes from the workers who entered no. 1 reactor building but according to news this was in the night of 11th day - so way after tsunami:


http://www.nuclearevents.info/ines-scale/level-7/fukushima-daiichi-japan-level-7-update-may-16-2011/ [Broken]

Something TEPCO has confirmed is that at 18:30 pm (12th of March) they measured 0.07 micro-Sv/h neutrons - so this is also after tsunami:



http://www.geocities.jp/swingi70/_gl_images_/P1020249toudenn.jpg

Summary:
11th of March 3:29 pm - the monitoring post went off
in the night of 11th of March - dosimeters showing 300 mSv/h inside the no. 1 reactor
12th of March 18:30 pm - 0.07 micro-Sv/h neutrons confirmed
Radiation instrumentation is generally designed to alarm on instrument failure as well as high radiation levels. Specifically an instrument may alarm on power supply failure, downscale or offscale high indications that are not actually associated with an actual high radiation condition. I looked for details of events at 15:30 on March 11 and found that TEPCO reported the initial tsunamis waves arrive on site at 15:27. http://www.yomiuri.co.jp/dy/national/T110410003477.htm [Broken]
This could explain a radiation alarm at one monitoring station, but not others. As subsequent waves of the tsunami arrived further failures may have been masked by the large number of alarms from equipment inundation, loss of emergency AC power and loss of power to control rooms.

If anyone has a specific location of which alarm was triggered, it could be checked to see if it was close to the water or not.
 
Last edited by a moderator:

tsutsuji

Gold Member
1,219
15
http://news.tbs.co.jp/newseye/tbs_newseye4805648.html [Broken] Government-related sources have said that because the construction of the ground water shielding walls will take 2 years, Tepco is studying a new kind of waterproofing work. What is planned is to pump up the contaminated water from the drain trenches, and then fill up those trenches. An experiment will be performed at units 5 and 6. If it goes fine, it will be extended to units 1, 2 and 3.
 
Last edited by a moderator:

tsutsuji

Gold Member
1,219
15
For people who are curious about this Tepco 24 May press release "Submission of a report on investigation of causes of damage situation of power facilities inside and outside of Fukushima Daiichi Nuclear Power Station to NISA" which was never translated into English, I found that the NISA's evaluation, which contains much of what Tepco said on that topic is available in English on the NISA website :
In particular, where the NISA paper vaguely says "Furthermore, TEPCO mentions that it will continue to investigate the causes of the damage", the Tepco report of 23 May ( http://www.tepco.co.jp/cc/press/betu11_j/images/110524d.pdf ) contains detailed schedules on pages 10-11, planning to create models of the earthquake wave and equipments by the end of July or August, then perform earthquake resistance analysis, and reach conclusions on the causes of equipment damages by the end of December (units 1 & 2 switchyard) or by the end of November (Shin-Fukushima substation). I hope they will be able to tell more about the embankment collapse that caused the Yonomori tower 27 collapse.
 
Last edited by a moderator:

NUCENG

Science Advisor
914
0
According to Bloomberg's original news the monitoring post was set to go off at high levels of radiation. But I guess if there would have been high levels of radiation 1.5 km from the no. 1 reactor also some other monitoring posts would have been triggered?

Surely this cannot be the only monitoring post at the Fukushima plant, can it?

http://www.bloomberg.com/news/2011-05-19/fukushima-may-have-leaked-radiation-before-quake.html [Broken]



Why has TEPCO not given us any more information about this monitoring post? Or have they?

The next information about possible radiation comes from the workers who entered no. 1 reactor building but according to news this was in the night of 11th day - so way after tsunami:


http://www.nuclearevents.info/ines-scale/level-7/fukushima-daiichi-japan-level-7-update-may-16-2011/ [Broken]

Something TEPCO has confirmed is that at 18:30 pm (12th of March) they measured 0.07 micro-Sv/h neutrons - so this is also after tsunami:



http://www.geocities.jp/swingi70/_gl_images_/P1020249toudenn.jpg

Summary:
11th of March 3:29 pm - the monitoring post went off
in the night of 11th of March - dosimeters showing 300 mSv/h inside the no. 1 reactor
12th of March 18:30 pm - 0.07 micro-Sv/h neutrons confirmed
If the modeling of the Unit 1 accident progression here (p32) is correct the core uncovery and temperatures could easily cause enough fuel damage to explain the radiation readings on the night of 3/11,
http://dels.nas.edu/resources/static-assets/nrsb/miscellaneous/SekimuraPresentation.pdf
 
Last edited by a moderator:
798
30
If the modeling of the Unit 1 accident progression here (p32) is correct the core uncovery and temperatures could easily cause enough fuel damage to explain the radiation readings on the night of 3/11,
http://dels.nas.edu/resources/static-assets/nrsb/miscellaneous/SekimuraPresentation.pdf
Yes, but why should one believe a model is correct, when it is free floating, quite detached from, and indeed inconsistent with any salient real world observation of water levels and entry in the operator logs?
 
There's still plenty of I-131 left 5 months after the scram, even though it has halved every 8 days.
Define "plenty". 5 months is 20 half-lives. Which means only one millionth of initial quantity of I-131 still exists.
 
244
1
Define "plenty". 5 months is 20 half-lives. Which means only one millionth of initial quantity of I-131 still exists.
If the initial quantity was of the order of 1e18 Bq per core, there would still be 1e12 Bq per core left (part of which was released to the environment).
 
1,045
2
If the initial quantity was of the order of 1e18 Bq per core, there would still be 1e12 Bq per core left (part of which was released to the environment).
You know, you are right, but this talk of re-mobilized iodine, mixing etc gets more improbable by the half-life. What is the mechanism you propose, by which Iodine that was produced before the accident is only now being added to the water, in ever-increasing doses?

EDIT: to clarify, the doses MUST be increasing exponentially, because otherwise the concentration would not remain so near constant.

How does that work?
 
244
1
You know, you are right, but this talk of re-mobilized iodine, mixing etc gets more improbable by the half-life. What is the mechanism you propose, by which Iodine that was produced before the accident is only now being added to the water, in ever-increasing doses?
I am not proposing anything, just trying to comment that this matter is not as straightforward as one might think at first. Iodine chemistry, migration of the iodine inside the pellets that have not melted before, possible later damaging of the fuel rods that did not lose their integrity at the very beginning. Addition of boric acid to the injected coolant (I don't know if it has been done recently or not), damage of instrumentation cabling lowering the pH of water and causing iodine to escape.. And based on the experiences so far, one should not be overly optimistic about the accuracy of the gamma analyses either - I don't know if TEPCO has so far allowed anyone else to analyze the samples they have taken, and they apparently made some rather crude errors in the early analyses (remember the Cl-38 they first reported and then withdrew).

My point was only that one should not jump to too hasty conclusions on inconclusive data, but instead try to objectively analyze it and consider all possibilities before making any claims in one direction or another. A couple of more months will give us a better picture of how the iodine concentrations will behave.

EDIT: To add: if there was ongoing criticality, it should lead to a wide number of short-lived isotopes being generated, such as I-135 and Xe-135, and their presence would be a certain indication of a recent criticality. On the other hand, I am not sure how TEPCO:s analysis and reporting routines would contribute to presence of such isotopes becoming reported. It appears that only I-131, Cs-134 and Cs-137 are routinely reported, but I don't know it a more complete gamma analysis is made on routine samples.
 
Last edited:
1,045
2
I am not proposing anything.

EDIT: To add: if there was ongoing criticality, it should lead to a wide number of short-lived isotopes being generated, such as I-135 and Xe-135, and their presence would be a certain indication of a recent criticality. On the other hand, I am not sure how TEPCO:s analysis and reporting routines would contribute to presence of such isotopes becoming reported. It appears that only I-131, Cs-134 and Cs-137 are routinely reported, but I don't know it a more complete gamma analysis is made on routine samples.
It's not clear at all that such spectrum analyses are performed at all. Anyway, it all hinges on an even simpler question: have there been more neutron flux spikes? TEPCO isn't saying.
 
1,045
2
migration of the iodine inside the pellets that have not melted before, possible later damaging of the fuel rods that did not lose their integrity at the very beginning
TEPCO and NISA say "three complete meltdowns". Means 100% of volatiles get released from the fuel. And anyway, how does some of the fuel melt down "later"?

. Addition of boric acid to the injected coolant (I don't know if it has been done recently or not), damage of instrumentation cabling lowering the pH of water and causing iodine to escape.
Escape fom where? What insolube iodide salts could have formed, that only now break up due to lower pH from boric acid which has been added, basically, from day one? How come there's so much of these salts that the concentration of radio-iodine in water remains essentially constant, instead of decaying exponentially as it should?

EDIT: to clarify, I think the simplest answer is "ongoing criticality". It may be not the correct one. But there must be an answer. It's too late in the game to dismiss this as a fluke of chemistry, I think.
 
14
0
TEPCO and NISA say "three complete meltdowns". Means 100% of volatiles get released from the fuel.
What about chemically reactive volatiles?
 
244
1
TEPCO and NISA say "three complete meltdowns". Means 100% of volatiles get released from the fuel. And anyway, how does some of the fuel melt down "later"?
IIRC, the statement on core status was changed from some freak percentage number of core damaged (based on direct interpretation of the CAMS values?) to "complete meltdown" in mid-May, after they recalibrated their level measurement sensors and the new reading showed the cores to be fully exposed. Then they made calculations based on the assumption that none of the seawater pumped by the firefighting system in the early stages of the accident entered the core and got a complete meltdown as an unsurprising result of that calculation.

I am not sure if they have later released any justification for the presumption that the seawater cooling was such a complete failure, and am therefore hesitant to take that statement of full core meltdowns as a given fact. If the cores have melted totally, then of course all iodine has escaped, but if part of the rods contrary to that remained intact and lost their integrity (note: i am not saying "melted") later, then their gas gap inventory would also have been released to the containment at a later stage.

Note: I am not claiming that any of this happened, I am only justifying my reluctance to jump to conclusions based by random (or selectively chosen) pieces of information. Detailed data on isotopic concentrations of all gamma emitters in the water found in the basements would give a better understanding of the situation until the core status can be verified directly, but so far we're in my opinion guessing on very thin data.


EDIT: to clarify, I think the simplest answer is "ongoing criticality". It may be not the correct one. But there must be an answer. It's too late in the game to dismiss this as a fluke of chemistry, I think.
Ongoing criticality is of course also possible, but it is made less probable by assuming a complete core meltdown, as the molten core lacks a proper geometry from moderation point of view. And it should be notable by other things as well instead of just one measurement curve of I-131 in a place far away from the reactors that seems to go down slower than the decay rate would imply. And if there are no other signs of criticality, such as neutrons or short-lived radioactive nuclei leading to increased dose rates close to the reactor, one can also ask, what would be the need for an urgent answer? You can always stop the fissions by increasing the boron content in the cooling water, but if there are no direct indications of fissions, it would not be necessary.

I am very interested in finding out the status of the cores, but I want the information to be coherent and justifiable, and that means we'll probably need to wait until they get a camera into the containment. Until then - especially if the entire gamma spectrum of the coolant samples is not analyzed - I'm afraid there's not much we can do to improve our knowledge of the situation.
 

NUCENG

Science Advisor
914
0
Yes, but why should one believe a model is correct, when it is free floating, quite detached from, and indeed inconsistent with any salient real world observation of water levels and entry in the operator logs?
I have been working to understand the "real world levels and operator logs" since they were first published. I believe the operator logs are accurate but incomplete. At the rate things were moving I would bet that some log entries were not performed and I hope we will eventually see the results of reconstruction and debriefing of the operators that were there to fill in or confirm questions like the efforts to reinitiate IC flow, any temperatures that were observed during the periods that the instruments weren't recording, and what physical damage may have been observed prior to the tsunami.

As to levels, we have previously discussed the level instrument reference leg and condensing chamber designed to keep the reference leg full. Once containment temperatures exceeded the boiling point the level of the reference legs would have been unknown. Any shortage of water in the reference leg causes a non-conservative high indicated water level. I don't believe we actually had any "real life" level data after a few hours.

I have worked with thermo-hydraulic codes accident modeling, dose consequencesw analysis, and fuel design calculations for years. While we have never had an actual "Fukushima" meltdown and containment failure before this year as a proof of the modeling codes like MAAP and RETRAN and numerous others, there have been events that were not so severe that have showed these codes give a good representation of those events. Certainly they have more validity than some of the wild speculation on the net and in the media.

I don't know if you have heard about the draft SOARCA report obtained by UCS.

http://pbadupws.nrc.gov/docs/ML1119/ML111920647.html

It actually discusses an unmitigated SBO for an American BWR4 (RCIC) The consequences are similar to what we see at Fukushima (no prompt radiation fatalities).

In the end, I am not asking you to trust the codes and models. I don't completely trust them and that is because many of the necessary inputs are still unknown. However, I will ask you to consider that there may be enough agreement between these models and what we know about Fukushima, that we can start there in our discussions. If we find things that don't fit, that is worth knowing.

Probably the best I can say about the SOARCA and MAAP analysis performed by Dr. Sekimura is that the codes implement physical principles that produce outputs and consequence predictions that are mathematically determined from the inputs used based on all the research and knowledge that we have learned from previous events and accidents. Look at all the different theories and speculations that have been bantered around about the damage to Unit 4 (SFP Hydrogen burn and detonation, Radiolysis and H2 gas burn, Physiscal damage from the earthquake that the NRC Chairman though had emptied the pool, H2 from Unit 3 to Unit 4 through the common stack piping, etc.) Look at the Unit 3 explosion thread. I think the analysis models should at least get that same level of attention. They may be wrong, but they could be right.
 
Last edited by a moderator:

Related Threads for: Japan Earthquake: nuclear plants

Replies
6
Views
15K
Replies
2K
Views
371K
  • Last Post
3
Replies
73
Views
19K
  • Last Post
Replies
17
Views
8K
Replies
10
Views
10K
  • Last Post
Replies
14
Views
12K
Top