Japan Earthquake: Nuclear Plants at Fukushima Daiichi

In summary: RCIC consists of a series of pumps, valves, and manifolds that allow coolant to be circulated around the reactor pressure vessel in the event of a loss of the main feedwater supply.In summary, the earthquake and tsunami may have caused a loss of coolant at the Fukushima Daiichi NPP, which could lead to a meltdown. The system for cooling the reactor core is designed to kick in in the event of a loss of feedwater, and fortunately this appears not to have happened yet.
  • #10,956
rmattila said:
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.
 
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  • #10,957
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'
 
  • #10,958
Something weird happened to R2's temperatures around 29th June..

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


WnNVr.png
 
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  • #10,960
Bodge said:
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 ).

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
 
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  • #10,962
~kujala~ said:
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



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/

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
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.
 
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  • #10,963
http://news.tbs.co.jp/newseye/tbs_newseye4805648.html 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.
 
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  • #10,964
tsutsuji said:
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.
 
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  • #10,965
~kujala~ said:
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



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/

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
 
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  • #10,966
NUCENG said:
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?
 
  • #10,967
rmattila said:
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.
 
  • #10,968
nikkkom said:
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).
 
  • #10,969
rmattila said:
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?
 
  • #10,970
zapperzero said:
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.
 
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  • #10,971
rmattila said:
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.
 
  • #10,972
rmattila said:
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.
 
  • #10,973
zapperzero said:
TEPCO and NISA say "three complete meltdowns". Means 100% of volatiles get released from the fuel.

What about chemically reactive volatiles?
 
  • #10,974
zapperzero said:
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.
 
  • #10,975
MadderDoc said:
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.
 
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  • #10,976
zapperzero said:
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?

The distribution of radioiodine is just as likely to be spread unevenly as Cs-137. You have seen reports of hotspots and local radiation fields. Why is it so hard to believe that there may be hotspots of I-131? The graphs of iodine show iodine in some samples but not others. The water in the basements and in the radwaste building is being stirred up by water processing to some extent, but is not at any rate sufficient to produce a uniform mixture, especially if it is in terms of sludge or deposited isotopes.

While recriticality is a possible explanation, it has to be at a very low rate or we would see the I-131 showing up in consecutive samples demonstrating a decay rate. Instead what we see seems to be interemittent samples folllowed by gaps until it appears again.

I have said it before. Half of a big number is still a big number. The 20 half-lives for I-131 since the reactors shutdown produce about 6 orders of magnitue of decay. But when you start off with numbers of 10^17 or 10^18 Bq, you can still expect to see I-131 for quite a while.
 
  • #10,977
NUCENG said:
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

I think this has been discussed before so I am making here a short summary.

From this (Japanese) TEPCO log one can find a log entry at 23:14 on the 11th day containing the words "300 mSv/h" which must be the same event we are talking about:
http://www.geocities.jp/swingi70/_gl_images_/P1020249toudenn.jpg

The first waves of the tsunami arrived at 15:27 and at 15:37 all generated electrical power was lost.
http://www.yomiuri.co.jp/dy/national/T110410003477.htm
http://en.wikipedia.org/wiki/Fukush...ling_problems_and_first_radioactivity_release

When this TEPCO log entry was first published there was some speculation in the newspapers that loss of power alone would not have been able to cause this high of radiation so early without earthquake causing some serious damage to the pipes and the RPV/the containtment. Even TEPCO admitted (at that point) that earthquake might have caused damage:

The source of the steam was believed to be the No. 1 reactor's overheated pressure vessel.

But for that scenario to hold, the pressure in the reactor would have to have reached enormous levels ~~~- damaging the piping and other connected facilities. It should have taken much more time to fill the entire building with steam.

A source at Tepco admitted it was possible that key facilities were compromised before the tsunami.

"The quake's tremors may have caused damage to the pressure vessel or pipes," the official said.
http://search.japantimes.co.jp/cgi-bin/nn20110516a3.html
(may 16th)

This announcement was made after TEPCO had already admitted the meltdown of the no. 1 reactor:
http://www.telegraph.co.uk/news/wor...9502/Nuclear-meltdown-at-Fukushima-plant.html
(may 12th)

However, NUCENG said earlier that it's very difficult to overpressurize the RPV because of the Safety Relief Valves:
https://www.physicsforums.com/showpost.php?p=3322467&postcount=8225

I think the workers were outside the containtment when they measured this 300 mSv/h.

The design capacity of the containtment was about 400 kPa. From the log entry here we can see that at 0:12 on 12th it was 600 kPa :
http://www.geocities.jp/swingi70/_gl_images_/P1020249toudenn.jpg

So it was about one hour after they had measured 300 mSv/h outside the containtment that the pressure was 1.5 times the allowed inside the containtment.

If we assume that the earthquake did no serious damage to the RPV, the pipes and the containtment to me it seems that the containtment starts loosing its integrity quite soon after the design basis has been exceeded. So there is really not a lot of loose margin.

But I guess that's the way it's supposed to go.

(Edit: We must of course take into account also the temperature which must have exceeded the design basis, too.)
 
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  • #10,978
~kujala~ said:
I think this has been discussed before so I am making here a short summary.

From this (Japanese) TEPCO log one can find a log entry at 23:14 on the 11th day containing the words "300 mSv/h" which must be the same event we are talking about:
http://www.geocities.jp/swingi70/_gl_images_/P1020249toudenn.jpg

The first waves of the tsunami arrived at 15:27 and at 15:37 all generated electrical power was lost.
http://www.yomiuri.co.jp/dy/national/T110410003477.htm
http://en.wikipedia.org/wiki/Fukush...ling_problems_and_first_radioactivity_release

When this TEPCO log entry was first published there was some speculation in the newspapers that loss of power alone would not have been able to cause this high of radiation so early without earthquake causing some serious damage to the pipes and the RPV/the containtment. Even TEPCO admitted (at that point) that earthquake might have caused damage:


http://search.japantimes.co.jp/cgi-bin/nn20110516a3.html
(may 16th)

This announcement was made after TEPCO had already admitted the meltdown of the no. 1 reactor:
http://www.telegraph.co.uk/news/wor...9502/Nuclear-meltdown-at-Fukushima-plant.html
(may 12th)

However, NUCENG said earlier that it's very difficult to overpressurize the RPV because of the Safety Relief Valves:
https://www.physicsforums.com/showpost.php?p=3322467&postcount=8225

I think the workers were outside the containtment when they measured this 300 mSv/h.

The design capacity of the containtment was about 400 kPa. From the log entry here we can see that at 0:12 on 12th it was 600 kPa :
http://www.geocities.jp/swingi70/_gl_images_/P1020249toudenn.jpg

So it was about one hour after they had measured 300 mSv/h outside the containtment that the pressure was 1.5 times the allowed inside the containtment.

If we assume that the earthquake did no serious damage to the RPV, the pipes and the containtment to me it seems that the containtment starts loosing its integrity quite soon after the design basis has been exceeded. So there is really not a lot of loose margin.

But I guess that's the way it's supposed to go.

(Edit: We must of course take into account also the temperature which must have exceeded the design basis, too.)

It might be my imperfect command of english, but I am not sure i understand your conclusion.
Are you leaning toward the idea that early damage to pipes, did in fact happen before the tsunami wave struck ?
 
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  • #10,979
~kujala~ said:
This announcement was made after TEPCO had already admitted the meltdown of the no. 1 reactor:
http://www.telegraph.co.uk/news/wor...9502/Nuclear-meltdown-at-Fukushima-plant.html
(may 12th)

To add to that, my recollection is that on May 12th TEPCO announced that the core of unit 1 had melted, but it was only three days later, on May 15, that they justified this statement by giving out the information that the isolation condenser would have been inactive since the arrival of the tsunami: http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110515e10.pdf.This information, which is still somewhat vague (what happened at 18:18 and 18:25, and was the system operable at all), would mean that the core damages would have started around 18:00, and proceeded to a meltdown within a couple of hours.

The following is my own speculation: if the IC really was closed for some incomprehensible reason between 15:30 to 18:18, and the steam-Zirconium reaction started to accelerate around 18:00, it could mean that there was enough accumulated hydrogen in the RPV by 18:18 to prevent steam from entering the IC, and this could explain the "no steam" notion discussed a couple of pages ago.
 
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  • #10,980
Luca Bevil said:
It might be my imperfect command of english, but I am not sure i understand your conclusion.
Are you leaning toward the idea that early damage to pipes, did in fact happen before the tsunami wave struck ?

No, I am saying that 300 mSv/h can be explained by the meltdown and rising pressure/temperature which exceeded the design basis of the containtment. I think NUCENG also meant this.

The only "point" I wanted to make was that for this to happen the containtment probably has not much "safe margin" and starts to brake into peaces quite soon after the design basis has been exceeded.

Of course this is not the only possible explanation, but anyways this 300 mSv/h could be explained without "mysteries". :cool:
 
  • #10,981
NUCENG said:
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.<..>

That may well be, but the assumption that some observations are missing does not allow the model to disregard existing observations. According to the operator log, the operator observed IC to be operational at about 18:18-18:25 on March 11th, and again at 21:30, while the model assumes the function of IC to have been lost at SBO, at about 16:00 on March the 11th,

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. <..>

Yes I understand that, but the model we are talking about does not have the PCV temperature exceeding that boiling point until about 9-12 hours after those water level data readings which the model needs to dismiss.
 
  • #10,982
~kujala~ said:
starts to brake into peaces

Sorry, I meant: break into pieces... :redface:
 
  • #10,983
There was some discussion of the CAMS units at Fukushima a while ago. I am at the Texas A&M Cyclotron right now, and they have a CAMS here. I looked for the manual but could not find it in the repository for manuals. But, I did get a good look at the unit. It is about a 12 x 12 x 6" box, with a paper filter and a small Silicon detector. I think the vacuum pump to suck air through the filter is external. The filter paper is on a roll and is advanced at regular intervals. So, this unit requires maintenance to replace the filter paper every so many days. Also, if it is exposed to steam or high amounts of water vapor, the filter paper is likely to disintegrate like wet toilet paper, and make the unit stop functioning.

Jon
 
  • #10,984
hello,

I personnally want to adress great thanks to the chemist who create the ' gum' that fill the hole of daichii fukushima (the leak were 3 months )

now the only way is to learn to live with a scrappet of a maximum of nuclear power plant.

best regards
 
  • #10,986
Bodge said:
Looks like, in the early days of the crisis, significant quantities of U-239 were able to migrate at least 35km from FUK-1.

https://www.physicsforums.com/showpost.php?p=3462692&postcount=221

Not good news.
Does that not imply burning fuel, or at least boiling uranium? It seems plausible given the reality of several meltdowns, but it also implies a much dirtier site if there are uranium and neptunium deposits outside of the containments.
 
  • #10,987
Bodge said:
Looks like, in the early days of the crisis, significant quantities of U-239 were able to migrate at least 35km from FUK-1.

https://www.physicsforums.com/showpost.php?p=3462692&postcount=221

I couldn't see exactly when the samples were taken, but the rough parity between iodine and cesium radiation levels in those figures suggests it was perhaps around the second week of April, based on published isotope distribution in Tokyo drinking water at the time. That would be roughly 10 half lives of Np-239, or three orders of magnitude of decay from scram levels. That would move it from several 10^2 Bq/kg to several 10^5 Bq/kg at release time, if the release was around the initial meltdown events. Given that Np-239 decays to Pu-239 with 24,000 years half life, that's certainly not good.

What puzzles me though is that uranium, neptunium and plutonium are not particularly volatile, especially in oxide form. They do not readily vaporize, unless there's extreme heat or a massive explosion. With the normal vent path, the gasses from the core would first be scrubbed through the suppression chamber water. I would imagine that most of these heavy oxides that make it into some kind of aerosol during a fuel rod fire or meltdown would be trapped at that stage.

We've had some debate in the unit 3 explosion thread about a leak from the unit 3 containment through the lid into the 5F/RF space during the explosion there. That is more like the kind of vent path that would be necessary in my opinion to get such high doses of heavy oxides into the plume.

On the other hand, given that the Np-239 should have decayed to Pu-239 by now, which is not going to disappear any time soon, I would like to see the actinide contamination levels to the NW of F-1 confirmed before we speculate too much.
 
  • #10,988
joewein said:
What puzzles me though is that uranium, neptunium and plutonium are not particularly volatile, especially in oxide form. They do not readily vaporize, unless there's extreme heat or a massive explosion.

Indirect evidence for recriticality keeps mounting, iow? :frown:
 
  • #10,989
""I would imagine that most of these heavy oxides that make it into some kind of aerosol during a fuel rod fire or meltdown would be trapped at that stage.""

there was venting and water injection in those early days.

My guess would be aerosols, and responsible for those small neutron readings at main gate too.

were levels "Significant" or detectaible ? I can't make out the numbers in that link.

old jim
 
  • #10,990
zapperzero said:
Indirect evidence for recriticality keeps mounting, iow? :frown:

I'd be more inclined to believe in recriticality if iodine levels exceeded cesium levels again and sampling around the site perimeter spiked, which it hasn't really since the end of March:

http://fukushima.grs.de/sites/default/files/Entwicklung_ODL.jpg"

http://fukushima.grs.de/sites/default/files/Messpunkte_Reaktorgelaende.jpg"
 
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