Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[ManuBZH]

Why unit 4 sfp is only 2300mm ?

This is the skimmer surge tank water-level reading, not the pool itself.
Current temperature readings (90~91°C) are nearing boiling point which increase evaporation. Looks like they'll have to use the "giraffe" concrete pump to pour some fresh water soon...

 

[Enthalpy]

Against the presence and amount of ³⁸Cl, I found then a convincing argument, because it doesn't depend on models about the health of the fuel cladding, the relative positions of sea water and fuel, and so on.

That was, ²³Na would have been at the same place as ³⁷Cl and would have produced very similar amounts of ²⁴Na, which is as well a very detectable gamma emitter, with a half-life longer than ³⁷Cl but short enough that its activity would have been much stronger than other nuclides mentioned in the analysis.

So: as no ²⁴Na was observed, ³⁸Cl must have been a mistake.
http://saposjoint.net/Forum/viewtopic.php?f=66&t=2657&start=160#p31368

 

[Joe Neubarth]

Has this already been discussed to death?

http://www.technologyreview.com/blog/arxiv/26738/

Perhaps, but it seems to disprove a Prompt Criticality Explosion in the SFP of Reactor Three.

 

[Astronuc]

Fukushima cover on its way
http://www.world-nuclear-news.org/RS-Fukushima_cover_on_its_way-2706118.html
27 June 2011

Interestingly,

Unit 1 spent fuel 'sound'

Nuclide analysis of water from the spent fuel pool at unit 1 suggests that most of the fuel in the pool is sound, Tepco reports. The analysis of 300 millilitres of water from the pool on 22 June showed higher activity levels than would be expected under normal conditions, but this is assumed to arise from contamination by radioactive materials from rubble, dust and incoming contaminated water.

We shall see.

 

[jim hardy]

@ Fine

you have my sympathy - looking at photos drives one to see things. Driven crazy? With me it's just a putt.

Whatever shape i am looking for appears everywhere - it's a quirk of human brain i think we are programmed by Mother Nature to look for patterns.

I find circles everywhere so always look for same object in at least two photos.

this shadowy circle i take to be an optical illusion or figment of my imagination. Many people won't see one at all others will think there's something round buried under the dirt.
Mark Twain called it "Excess of Imagination" , i call it "The curse of Creativity" and work to keep mine in rein.

i've got a mental note it's there and will keep an eye out for better photo of same area. But i don't expect to find anything there.

So, keep on looking but cross check yourself !

 

[joewein]

This is the skimmer surge tank water-level reading, not the pool itself.
Current temperature readings (90~91°C) are nearing boiling point which increase evaporation. Looks like they'll have to use the "giraffe" concrete pump to pour some fresh water soon...

On 16 June 2011 they switched from the "giraffe" (Putzmeister truck pump) to the pool cleaning and cooling system using a new spout hooked up to a handrail above the pool. They no longer use the truck pumps for refilling at any of the pools.

See "water injection and spraying to spent fuel pools" (page 3) in:
http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_110621_04-e.pdf

What they really need is not just a refill but a heat exchanger.

 

[Arizonan]

I do not at all see how this report disproves the prompt criticality event hypothesized for SFP 3 on March 14th. That material went straight up into the atmosphere. The measurements done for this article were only done with reactor water.

 

[robinson]

http://mdn.mainichi.jp/perspectives/news/20110627p2a00m0na004000c.html

More bad news.

 

[Fine]

@ Fine

you have my sympathy - looking at photos drives one to see things. Driven crazy? With me it's just a putt.

!

Thanks, I think the lack of info is driving everybody a bit batty.

 

[tsutsuji]

Fukushima cover on its way
http://www.world-nuclear-news.org/RS-Fukushima_cover_on_its_way-2706118.html
27 June 2011

We talked about the new details about the cover for unit 1 on page 639 of this thread. Basically the source of information is the following Tepco press release (English version) from June 24th:

Having seen more details about the temporary cover building for reactor 1, I quite like it.

http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110624e15.pdf

OK there are a few risks of things going wrong, but it should enable us to get a much better idea of what radioactive substances are still escaping, the opportunity to filter them, and better monitoring of things like the fuel pool.

http://www.mbs.jp/news/jnn_4762048_zen.shtml the closed loop cooling of the reactors (meaning reinjecting the decontaminated, desalinated water into the reactors) had to be stopped after one and a half hour of operation, after a leak of treated water was found.

http://www.nikkei.com/news/image-ar...XBZO3117681028062011I00001;R_FLG=0;z=20110628 : diagram showing the location of the leak, saying it is located in a hose coupling.

 

[PLG]

Hi all,

I am a newbie and something of an intruder around here (non-engineer, mere economic historian, and French to boot), but for personal reasons (Japanese friends) I have been following closely semi-public discussions of the crisis within the French nuclear establishment.

I have a question for you people: back where I come from, a lot of apparently knowledgeable people are in a pretty nervous state over the status of the molten fuel, i.e. corium. It seems that cooling it from above is a near impossibility -though I read a paper out of Argonne saying it actually could be done, cf.

http://article.nuclear.or.kr/jknsfile/v41/JK0410575.pdf

My folks rather rely on this

http://www.ornl.gov/info/reports/1981/3445600211884.pdf

(1981, thus old, but in English)

and this

http://www.irsn.fr/FR/Larecherche/p...bli/DSR/SAGR/Documents/rapport_RetD_AG_VF.PDF

(newer -2006- but in French. yeah, I know -useless)

The Mainichi piece just quoted

http://mdn.mainichi.jp/perspectives/news/20110627p2a00m0na004000c.html

confirms that at least some corium has escaped, and all the models the French at least are working with foresee no end to "installed" corium activity (and downward progression toward the water table), barring much more drastic measures than a few hundred tons of water on top.

Would you care to discuss the differing assessments of risks on each side of the Atlantic, and share your view of the corium situation? BTW "all froggies are yellabellied nogoodnik ignorants" does not qualify as a scientific answer...

Thanks to all for their wisdom!

Pierre

 

[etudiant]

Hi all,

I am a newbie and something of an intruder around here (non-engineer, mere economic historian, and French to boot), but for personal reasons (Japanese friends) I have been following closely semi-public discussions of the crisis within the French nuclear establishment.

I have a question for you people: back where I come from, a lot of apparently knowledgeable people are in a pretty nervous state over the status of the molten fuel, i.e. corium. It seems that cooling it from above is a near impossibility -though I read a paper out of Argonne saying it actually could be done, cf.

http://article.nuclear.or.kr/jknsfile/v41/JK0410575.pdf

My folks rather rely on this

http://www.ornl.gov/info/reports/1981/3445600211884.pdf

(1981, thus old, but in English)

and this

http://www.irsn.fr/FR/Larecherche/p...bli/DSR/SAGR/Documents/rapport_RetD_AG_VF.PDF

(newer -2006- but in French. yeah, I know -useless)

The Mainichi piece just quoted

http://mdn.mainichi.jp/perspectives/news/20110627p2a00m0na004000c.html

confirms that at least some corium has escaped, and all the models the French at least are working with foresee no end to "installed" corium activity (and downward progression toward the water table), barring much more drastic measures than a few hundred tons of water on top.

Would you care to discuss the differing assessments of risks on each side of the Atlantic, and share your view of the corium situation? BTW "all froggies are yellabellied nogoodnik ignorants" does not qualify as a scientific answer...

Thanks to all for their wisdom!

Pierre

Hi Pierre,
Afaik, you've got the major open corium studies listed. Note there may be Russian, Japanese or German studies that are unknown to me.
The conclusion, that the development of a large corium release is inadequately understood and poorly modeled is well recognized. The only ray of light is that the thermal output of the core material at this stage is relatively small, a few megawatts at worst. That will limit the scale and speed of any melt through the dry well floor. Also, there will be gradual mass loss of the corium from the time it escapes the RPV, as bits are left behind as slag, which also helps improve the cooling effort. But the reality is that there is no way to cool it. To freeze it, it would be necessary to break it apart to allow more access to the cooling water.
Presumably the greatest concern is of a steam explosion if the corium melts into a water bearing layer.
At this stage, that seems less likely. The thermal heat would produce only a few pounds of steam every second, not enough for a big blast unless the steam were confined for a period.

 

[Most Curious]

http://mdn.mainichi.jp/perspectives/news/20110627p2a00m0na004000c.html

More bad news.

The accuracy of some points in that article might be subject to considerable debate, IMHO.

 

[jim hardy]

Well PLG the closest i ever got to France was Quebec. Cold climate but great folks.

What i noticed real early on is, as soon as the shock&awe was over they tried to follow the steps in this document:

http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/24/072/24072657.pdf

namely depressurize, feed carefully and borate, and flood the containment so as to cool vessel from outside.

here's one on failure modes of vessel bottom

http://www.osti.gov/bridge/servlets/purl/6124656-R8y05j/6124656.pdf


my personal feeling, and it's not based on anything but reading stuff like above and watching what they do, is there's no China syndrome going but the alarmists are having a heyday. I would guess there's a debris bed in lower plenum as described in the studies and some leaks but not gross failure there.



so that's only my 0.014 Eu worth - i am as much a spectator as you.

From Arkansas to wherever you are - "Bonjour y'all, eh? "

 

[Most Curious]

Welcome, Pierre. This is a very diverse group here so I see no reason for you not to be made welcome. Interestingly, the French seem to be one of the more successful users of nuclear power, making their opinions & science of considerable interest.



On to my question:
I thought the theory of a "China Syndrome" for corium melting its way to the water table was no longer considered likely. Has that changed - again?



We all like to look at the Chernobyl accident as a source of data on a real world accident. The corium there was VERY hot at the time of the accident, little water was available to cool it yet the stuff is solidified in the basement(s) of the reactor building, not melting its way to the water table. I realize such a scenario was feared but does not appear to have occurred.

Why, then, would the Fukushima accident(s) be different? The cores are now much older since last operating with vastly reduced heat output as compared to Chernobyl. Has chemical evidence of breakdown of the DW floors been found and reported? (Or kept quiet like so much other data!) While top cooling is certainly not the best, has it been determined to be without effect? Does ANYONE know the real state of the corium - location and dispersion? I have yet to see such information.

 

[Joe Neubarth]

I do not at all see how this report disproves the prompt criticality event hypothesized for SFP 3 on March 14th. That material went straight up into the atmosphere. The measurements done for this article were only done with reactor water.

From the article:
"Matsui says the evidence comes from measurements of the ratio of cesium-137 and iodine-131 at several points around the facility and in the seawater nearby. He has calculated what the starting ratio must have been by assuming the reactors had been operating for between 7 and 12 months.

He says the ratios from drains at reactors 1 and 3 at Fukushima are consistent with the nuclear reactions having terminated at the time of the earthquake.

 

[LabratSR]

If anyone is interested, Ian Bradshaw has been doing a great job following the accident. He is graphing all the parameters daily and he has now started cataloging all the associated documents including all the Oak Ridge stuff posted here and elsewhere. He's also working on importing all the TEPCO docs and media. Worth checking out.

http://www.ianbradshaw.co.uk/multimedia/fukushima/

 

[Orcas George]

He says the ratios from drains at reactors 1 and 3 at Fukushima are consistent with the nuclear reactions having terminated at the time of the earthquake.

But do we know that the spent fuel pool at reactor #3 is leaking or ever overflowed? That would be big news in itself. I was under the impression that they were just "topping it up" to make up for evaporation, it certainly would not have been a great idea to deliberately overflow it. Given that reactors #1-#3 have holes in their containment (temp greater than boiling point but at atmospheric pressure) it seems more likely that the water in the basement is from there.

 

[Orcas George]

.

http://www.ianbradshaw.co.uk/multimedia/fukushima/

That is a good link but he is still stating that the amount of radiation released was "%10 of Chernobyl." First, the IAEA is talking about release of radioactivity into the atmosphere (not the ocean), secondly the estimates of the early releases have been raised. (http://online.wsj.com/article/SB10001424052702304432304576368890863809966.html), and thirdly the damn thing is still releasing significant amounts of radiation both into the atmosphere and the ocean.

However we are still selling the "only %10" line.

 

[LabratSR]

That is a good link but he is still stating that the amount of radiation released was "%10 of Chernobyl." First, the IAEA is talking about release of radioactivity into the atmosphere (not the ocean), secondly the estimates of the early releases have been raised. (http://online.wsj.com/article/SB10001424052702304432304576368890863809966.html), and thirdly the damn thing is still releasing significant amounts of radiation both into the atmosphere and the ocean.

However we are still selling the "only %10" line.

From your article.

" The latest figure is about 10% of the radiation released from the 1986 Chernobyl disaster, estimated at 5.2 million terabecquerels, NISA said."

 

[StrangeBeauty]

...a lot of apparently knowledgeable people are in a pretty nervous state over the status of the molten fuel, i.e. corium...

Correct me if I'm wrong, but the majority of fuel can only be a in a few places for all reactors:
1) the rpv, which is getting water
2) the bottom of the drywell, which has water in it
3) the basement, which is flooded with (highly radioactive) water
4) through the bottom of the basement, which would could trouble but appears very unlikely based on the other real world example we have, Chernobyl.
5) already washed out to the ocean

If I had to guess I'd say it's some combination of 1, 2, 3 and 5 for each unit. It's not clear what percentage of the fuel has been dispersed into the atmosphere, but obviously that has occurred to some degree.

My biggest concern for a worsening of the situation at the moment would be a typhoon or TS of any strength hitting the area, which could present significant issues for #3 above, leading to more of #5. Does any/all this sound reasonable to the expert crew here, or am I missing something?

 

[joewein]

But do we know that the spent fuel pool at reactor #3 is leaking or ever overflowed? That would be big news in itself. I was under the impression that they were just "topping it up" to make up for evaporation, it certainly would not have been a great idea to deliberately overflow it. Given that reactors #1-#3 have holes in their containment (temp greater than boiling point but at atmospheric pressure) it seems more likely that the water in the basement is from there.

The water in the basement of unit 3 is one order of a magnitude more radioactive than the water in the spent fuel pool of unit 3. Therefore I think at least the bulk of the radioactivity in the basement water must come from the reactor core, not the pool. At most, water from a leaking or overflowing pool could have diluted more radioactive water leaking from the containment.

The situation is similar in all four damaged units (1-4). Their SFP water cesium concentrations as a percentage of their reactor building basement water cesium concentrations:

• #1: 10%
• #2: 3% (skimmer surge tank)
• #3: 9%
• #4: <1%

 

[Jorge Stolfi]

So, has there been any explanation of what happened in unit #3 in the early morning of march 21? Pressure and temperature plots show that something really significant happened inside the RPV, just prior of the black smoke. CAMS data show something also happened around march 18. But there seems to be not a word of explanation in the reports. Or have I missed it?

 

[tsutsuji]

Cover structure in Onahama Port, picture taken by Kyodo news' helicopter : http://www.47news.jp/CN/201106/CN2011062801000432.html

 

[clancy688]

From your article.

" The latest figure is about 10% of the radiation released from the 1986 Chernobyl disaster, estimated at 5.2 million terabecquerels, NISA said."

770.000 Tbq compared to 5.200.000 Tbq is obviously more than 10%. 15% would be more accurate. But since they're using the nice expression "about", it's somehow right...

 

[MiceAndMen]

Correct me if I'm wrong, but the majority of fuel can only be a in a few places for all reactors:
1) the rpv, which is getting water
2) the bottom of the drywell, which has water in it
3) the basement, which is flooded with (highly radioactive) water
4) through the bottom of the basement, which would could trouble but appears very unlikely based on the other real world example we have, Chernobyl.
5) already washed out to the ocean

I think you can eliminate number 3. Directly under the middle of the drywell there is probably nothing but concrete down to the construction depth and then Earth below that. The "basement", as I understand it, is the dug out trench where the torus suppression pool sits, and that is not an excavation that extends below the entire drywell.

If that's the case then the corium would have to flow out of the RPV down into the pedestal area of the drywell, then radially outward for several meters (in fact the pedestal in some drawings is an enclosed concrete cylinder with its own access doorways), climb up to the level of the torus vent duct openings, and then flow several more meters until it entered the downcomers inside the torus itself. Total distance traveled horizontally would be measured in tens of meters.

I really don't think there is a physical path possible from the RPV straight down that hits anything except concrete, the steel drywell vessel, some sand, more concrete, and finally the Earth itself.

I could be wrong and if anyone can point to any of the TEPCO drawings that show any part of the "basement" capable of holding water that lies directly under the drywell I'd appreciate a link to it. But I don't think that's how the underground excavation for the torus is fashioned.

 

[SteveElbows]

and thirdly the damn thing is still releasing significant amounts of radiation both into the atmosphere and the ocean.

Says who? Data on continued emissions is limited, but we seem to see a picture where daily releases are not significant enough to cause appreciable new contamination away from the plant, nor do levels of radiation detected on site shoot up, not even after they opened the doors to reactor 2.

I think they estimated emissions past the early stages as being somewhere in the order of 1TBq per day. In terms of radioactive pollution in general, this is a significant amount, but compared to what already came out of Fukushima, it is not. Its not going to make an appreciable difference to the TBq total, so it won't make much difference to the percentage release comparisons with Chernobyl.

As for the oceans, again I see no evidence of continued high-magnitude leaks into the sea, nothing that compares with the large releases into the ocean in the earlier stages of disaster.

All of this leads me to believe that it will take a new event on site, or recalculations of earlier releases, in order to make a significant difference to the total release numbers. I could be wrong, as I am forming these conclusions based on data which may not be perfect or tell the whole story, but I certainly require evidence to support the claim of significant amounts of radiation continuing to be released.

 

[SteveElbows]

So, has there been any explanation of what happened in unit #3 in the early morning of march 21? Pressure and temperature plots show that something really significant happened inside the RPV, just prior of the black smoke. CAMS data show something also happened around march 18. But there seems to be not a word of explanation in the reports. Or have I missed it?

There has been precious little analysis or narrative about anything that happened past the first 5 days or so.

The entire period March 16th->March 24th interests me, rather than just one of the interesting smoke days, but I've reduced my expectations in regards to finding out more about this in the near future.

Also missing from most official analysis is much detail about any of the explosions, or the exact detail as to why reactor 2 is blamed for the vast bulk of the estimated releases, although we can make some assumptions in that regard.

The vast number of documents that have been released recently, comprising of faxes that TEPCO sent out over a period of months since the disaster began, may yet hold some detail about some of these things, but I am not sure they do. They are only available in Japanese and text cannot be copied & pasted from these documents, so without a Japanese speaker willing to sift through these for anything interesting, I am stuck.

http://www.nisa.meti.go.jp/earthquake/plant/plant_index.html

 

[elektrownik]

why unit 4 spf (or skimmer surge tank) is only 1400mm ?

 

[zapperzero]

Would you care to discuss the differing assessments of risks on each side of the Atlantic, and share your view of the corium situation? BTW "all froggies are yellabellied nogoodnik ignorants" does not qualify as a scientific answer...

Hi Pierre,

I think the corium is in different states, in the different reactors. My view is that it has probably stopped flowing, in all of them, and that if it hasn't, it still doesn't matter. It's cool enough to be covered in water by now, so there shouldn't be any problem with further releases into the atmosphere. The ground is contaminated heavily by radioactive water already.

Based on the (highly suspect) drywell CAMS data, I'd propose bits of corium dropping out of #1 RPV, as from a sieve, and total breaches of #2 and #3 RPVs, with corium ending up on the floor of the drywell more or less in one heap. #3 may have some still sticking to the walls, based on temp data.

I don't think the corium is recoverable in the short to medium term, by the way. This is not TMI.

EDIT: re-criticality seems a VERY remote possibility now, although I think we may still get nasty surprises with any of the reactors, should the boron content of the water fall.

 

[sheffters]

That is a good link but he is still stating that the amount of radiation released was "%10 of Chernobyl." First, the IAEA is talking about release of radioactivity into the atmosphere (not the ocean), secondly the estimates of the early releases have been raised. (http://online.wsj.com/article/SB10001424052702304432304576368890863809966.html), and thirdly the damn thing is still releasing significant amounts of radiation both into the atmosphere and the ocean.

However we are still selling the "only %10" line.

George, glad you find it useful.

However, just to clarify the 10% figure:

I am still quoting that number (not selling), which is sourced by the link provided on the page, as I have not yet seen any updated statistics from a credited national or international body as to the amount of radiation released. Additionally, everyone is estimating the amount released at the moment, so it is obviously subject to change. Given everyone is estimating, and the 10% figure comes from an accredited, sourced, agency and not a newspaper / magazine / crazy scientist with agenda, then that is the figure I stick with at the moment. If new information is released from IAEA, JAIF, NISA or other accredited body which can be sourced then I will update it. (I accept gov bodies also have agendas, but they are much more rigerously examined than a newspaper of lone ranger scientist, so they are the figures I tend to run with).

In the grand scheme of issues, whether its 10% or 15% doesn't really alter the point they are trying to make; i.e. the resulting radioactivity released will not currently have the same impact as Chernobyl. (Note: I am not saying if that is right or wrong, just what the people that know a lot more about nuclear than me are saying).

I am not a nuclear engineer, nor am I measuring the radiation. Therefore I can only go off what information is provided which I then provide sources as to where I get the information from.

I have also been concentrating on updating the graphs and charts on there a lot more than the guesstimated figures as these are factual pieces of information, not guesswork. You can ask 10 different people and get 10 different answers depending on how you measure it with regard to total release of radiation; it is the essence of the message that is important there, not the specific percentage that matters.

I try to keep an impartial view on it all and just provide the data for people to make their own judgements on as you can see from the Facebook updates. I'm not selling anything, just providing information and some background info on what I have learned whilst fukushima has been ongoing to give people who may have never read anything about nuclear some background as to what the numbers mean. Likewise with the text accompanying the graphs and charts, this is just what I have pieced together from varous sources (all linked) to give people an idea of what they are looking at. It should not be taken as a difinitive answer to the worlds problems, just my collection of information regarding the accident and nuclear background. There will be lots missing, lots to add, and lots to discuss from all sorts of places.

Cheers

Ian.

 

[joewein]

why unit 4 spf (or skimmer surge tank) is only 1400mm ?

The SFP is about 11 m deep, but the skimmer surge tank is much more shallow.

The two are connected via the overflow ports. Water gets added to the SFP so its level reaches the ports. From there it overflows waterfall-like into the surge tank. Pumps move it from there to a heat exchanger and a filter/demineralizer. Then it gets pumped back into the pool again.

That's the normal operation of the spent fuel pool cooling and cleaning system.

You can see a picture of the surge tank on page 37 and a diagram of the whole system on page 5:
http://www.docstoc.com/docs/77986256/Fukushima-Tragedy

(There are lots of other interesting pictures of BWR equipment there too.)

 

[PLG]

Hi all,

Thanks for the answers. A few more info, so as to share the little information I could read, and check if I actually understood the even smaller amount I am under the maybe delusional impression I did understand.

To Most Curious, #10285, re Chernobyl: again, if I have understood what I have read (a big if), a good deal of the nuclear fuel inventory was scattered around by the initial explosions; the total quantity of corium was anyway smaller than at Fukushima. Moreover the graphite control bars, which fed the fire in the core, also acted as impurities slowing neutron reactions within the corium. As a result the corium was less active than it could have been. Even then, according to the NEA report, the corium was turned off, so to speak, using 5000 tons of dry material (not water), including 40 tons of borate compounds, all of it dumped from helicopters. The corium was also fractioned using gravity and available ducts and spaces in the basement. Last but not least, this already significantly weakened corium, which had still managed to eat its way through the concrete floor, was countered with a specially constructed concrete mat built underneath its possible path, and which was to be cooled if there was need. In the end there was no need, which did indeed prove that a corium could stop -but that was through dry material attacks and fractioning, not water cooling from above. The thing is still pretty hot today, by the way, you wouldn't want to sit on it...

http://www.oecd-nea.org/rp/chernobyl/c01.html

By contrast, the papers I have read are not deliriously optimistic about dousing an active corium with water. Anyway, does not water get cracked way before getting at it? Water cracks at 700°C and the thing is well above 2000°C, so it generates oxygen and hydrogen rather than steam, no? Bottom line, I am not sure a corium turns off by itself once it becomes active after a criticality, the references I gave in my first post (#10281) make no mention of such an automatic switch-off process, and assume rather that the corium must be fractioned and cooled down to be containable.

And corium becomes active awfully fast, compared to Fuku1 timeline. Jim Hardy's doc (# 10284, thanks, and Hello Arkansas, do come over some time, Paris is as rainy as Seattle but at least it's not freezing, personal message) (and thanks for the papers) confirmed RPV failure at T0 + 7 hours or so in case of complete station blackout, but makes no mention of what happens next. The ablation rate of an active corium in the aforementioned references would make it able to eat through eight meters of solid concrete, including the embedded shell and the drywell wall, in 14 hours flat -that's the model from 1981. Also, I don't believe they added borate to their seawater at first, so it was just heat transfer, and eating a few neutrons here and there. A key point would be whether water got under the RPV before meltdown was effective, and that's not clear to me. If water had gotten under, they would not fret about RPVs being broken, would they? The effect of a corium falling into water would have been hard to miss even from far away...

If the RPVs are pierced as Tepco and the Japanese seem to say, these coriums were sure pretty active at some point, and went down without meeting water -we would have noticed otherwise, right? In this case, while a "China syndrom" is indeed not possible if I read what I read correctly, I was not referring to that, nor to any dramatic post-leak event, just to a plain old contamination of the ground and the water table and eventually ocean, all of which is supposed to be countered by this concrete wall they talk about. By the way even an inactive corium, if it has pierced all barriers, can contaminate its environment I suppose?

Last but not least, I know this is hearsay, but from French nuclear engineers, so it's a little less than pure specualtion, anyway it seems that the concrete basemat was hollowed out for seismic resistance reasons at Fukushima. So the drywell and its embedded shell sit atop a cavity which could indeed act as core-catcher, provided the corium is cool enough.

Don't get me wrong, but recapping your various posts I am under the distinct impression that nobody is very sure of where that corium is exactly, if it's cooled, if it's divided (some French models from what I heard forecast division of the corium, part of it seeping down, part of it remaining stuck in the RPV and cooling down), and what energy it generates exactly.

By the way, as a way to say thanks, here is what is UNDER the concrete

http://en.scientificcommons.org/49101133

The Tomioka formation (p. 4) is two layers, 60m + 140m; both fairly soft, more or less impermeable sedimentary formations, first layer argilite over fine then coarser sandstone, second layer solid sandstone intespersed with sandy argilite and coarse sandstone. I was unable to find anybody having ever thought of corium-argilite interactions -yeah I know, no surprise there.

So, here is what I have understood: Jim Hardy better be right and the RPV not broken through! A corium generates a lot of energy in a few cubic meters with very high density, not the kind of stuff you want to leave lying around. If anybody has more info or papers or sources, please bring 'em on, to quote a well-known poet.

PG

 

[zapperzero]

Don't get me wrong, but recapping your various posts I am under the distinct impression that nobody is very sure of where that corium is exactly, if it's cooled, if it's divided (some French models from what I heard forecast division of the corium, part of it seeping down, part of it remaining stuck in the RPV and cooling down), and what energy it generates exactly.

We do what we can, with the data available. I've said this before, in this forum - if I was running the show, I'd stuff borescopes into the RPVs to see what I can see. I'm not.

Water cracks at 700°C and the thing is well above 2000°C, so it generates oxygen and hydrogen rather than steam, no?

.

I don't know about that. I guess we could have a hydrogen explosion every day if that were still happening.

 

[clancy688]

In the grand scheme of issues, whether its 10% or 15% doesn't really alter the point they are trying to make; i.e. the resulting radioactivity released will not currently have the same impact as Chernobyl. (Note: I am not saying if that is right or wrong, just what the people that know a lot more about nuclear than me are saying).

Oh yes, it will.

http://imgf.tw/182135955.jpg

Source: IRSN (French radioprotection and nuclear safety institute)

http://www.irsn.fr/EN/news/Documents/IRSN-Fukushima-Report-DRPH-23052011.pdf