Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[Jorge Stolfi]

May I ask that what kind of software did you used for that?

In case you are still interested, the C programs I used (pnmprojmap, pnmfftfilter, pnmxarith) are in
http://www.ic.unicamp.br/~stolfi/temp/jsprogs-2011-05-09.tgz
They are unix-based (gcc). You may need to hack the Makefiles to get them to compile in your system. The pnmfftfilter prog requires the FFTW library package (libfftw3.a, fftw3.h). The "-info' option of each program prints its manpage.

 

[v13]

Hello,

In case you are still interested, the C programs I used (pnmprojmap, pnmfftfilter, pnmxarith) are in
http://www.ic.unicamp.br/~stolfi/temp/jsprogs-2011-05-09.tgz
They are unix-based (gcc). You may need to hack the Makefiles to get them to compile in your system. The pnmfftfilter prog requires the FFTW library package (libfftw3.a, fftw3.h). The "-info' option of each program prints its manpage.

I'm not sure what you're trying to do but you may be looking for http://hugin.sourceforge.net/" . It creates panorama images in the way you described it and can use multiple images to create an HDR version. I've created a number of panorama images but I did not have much success in HDR mostly because I'm not very familiar with that. It also does lens correction and can use different projections.

 

[|Fred]

about http://dcbureau.org/201103151304/Nat...ber-three.html

It has, and as it was to some extend irrelevant, there was not much discussion about it.
If I may, What part of the article make you qualify it as explanation of "the deep involvement of the French gov't, regulators and AREVA itself "
The article is no so much about AREVA involvement, and strictly speaking and GE is more involved..

The article is about Robert Alvarez saying MOX does not work , because its hot
"One reason proponents of MOX reactor fuel support its use is because, once the fuel is burned in a reactor, it is so hot that terrorists would not be able to steal a fuel assembly"

and

Because terrorist may use it "Reprocessing was abandoned by the United States in the 1970s because of the dangers of weapons proliferation."

No to mention it's a French thing ...

Point is this is not so much of about physics but much more about political and divergent economical interest.. And it has always been.. Here is a partially declassified (old) CIA intelligence report on French MOX http://cryptome.org/0003/cia-fr-pu.zip

 

[zapperzero]

about http://dcbureau.org/201103151304/Nat...ber-three.html
It has, and as it was to some extend irrelevant, there was not much discussion about it.
If I may, What part of the article make you qualify it as explanation of "the deep involvement of the French gov't, regulators and AREVA itself "

So. I have been unattentive again. Sorry, real life keeps throwing me curveballs these days and my attention span isn't what it used to be.

I do not believe it irrelevant, even from a technical point of view. Tests of AREVA MOX fuel elements have ended badly in other places. There may be a common factor that makes them unreliable, such as, oh, say, French quality control (if you've ever owned a Renault you know of which I speak).

The article does not mention the involvement, but it has been visible and high-profile from day one almost.

Sarkozy was there specifically to talk about nukes, the French whatsitsname agency was first to break ranks and say that yep, Fukushima is a big problem indeed, Areva offered help early on and was accepted instantly (only the US achieved similar performance). I had been wondering why the interest - seems they're playing for the home audience as well, trying to look all grown up and responsible and efficient (la Hague has been a smoldering scandal in France since before it was put in operation).

 

[BlueCactus]

New pics of Fukushima NPP are released anounymously.
here, we can see it in slideshow.

http://seiga.nicovideo.jp/watch/sg21679

 

[zapperzero]

Better-quality videos of the ventilation op and the sfp. Same content, so ignore if you're not into image processing.

http://martynwilliams.posterous.com/fukushima-daiichi-reactor-1-4-latest-video

 

[ascot317]

Yeah, of course.

I think it's plausible that some tv producer added three loud booms to an otherwise "silent" video of a major explosion in a NPP. That helps to spice things up a bit, to "entertain" viewers so that they'll watch again next time.
Or just to make his own video stand out so that it's getting bought by foreign tv stations.
As I said, for me, that's very plausible.

But it's highly implausible that the same tv producer would add helicopter noise to an explosion video. Think about it, why should he do that? It doesn't spice up anything. Moreover, why should he replace three booms (if those are the real deal and were in fact recorded parallel to the video track) with boring helicopter noise? There is no logic in that.

So I'm guessing that the three booms are just ear candy, and that the "helicopter noise vid" from tagesschau is the real deal.

Erm, you still seem to believe that it must be a production just because one video has helicopter noise and the other hasn't. Like I said, the explosion sound doesn't have to come from the supplier of the video. That does not mean it's not authentic. A different unit/person could have had an audio recorder running at that time, just no camera, or had the camera aimed at something else.
News channels usually pay for video and don't care much for the audio (when's the last time you had nobody talking on a news channel). So faking sound to make more money is rather unlikely.

 

[|Fred]

New pics of Fukushima NPP are released anounymously.
here, we can see it in slideshow.

http://seiga.nicovideo.jp/watch/sg21679

Could you please upload them elsewhere, in order to share them with non Japanese readers
that's about 80 pictures it seems

 

[mrcurious]

A question for the brilliant people on this thread regarding the explosion in #3.

Assuming the top of the reactor building had filled with hydrogen and that the water in SFP had dropped considerably exposing and partially melting a portion of the fuel rods, would the force of the explosion down the SPF onto the top of the water act as if it was hitting concrete thereby pushing the force of the explosion back up taking the exposed fuel rods and assemblies with it?

 

[|Fred]

This seems to me unlikely, then again I'm not one of the brightest of the crowd

 

[~kujala~]

But are they out of order? or is there something happening in the reactor that we are not supposed to know or deduce from their data, now look at the temperature plot, on the same day 8th April there was a sudden spike coinciding with the spike of the CAMS data

Could it be ... that the sudden spike of temperature on April 8th is somehow related to the nitrogen operation?

April 6th 22:30 Started the operation for the injection of nitrogen to PCV.
April 7th 01:31 Confirmed starting the injection of nitrogen to PCV.

http://www.nisa.meti.go.jp/english/files/en20110504-1-2.pdf

Also by some strange coincidence this nitrogen operation might have messed with CAMS drywell?

 

[pdObq]

OMFG did you saw CAMS data 3/14 for unit 3 ? It is error or 100% of unit 1 core is damaged

You mean unit 1? Did you see D/W value for 4/8 ?

added: Does anyone have an idea at what level those sensors saturate or get damaged?

pdObq, it's better to look the overall trend, not some big values every here and now.
For the unit 1 it mostly makes sense until April 7th 18:00 (31,1 Sv/h), then you suddenly get these mega values after which CAMS D/W(A) stops working.
I wouldn't trust the values between April 8th 0:00 - April 8th 13:00 for the unit 1.

Hmmm, the sudden high readings at 4/8 coincide with the sudden temperature rise of that N4B sensor (sorry, too lazy to put the japanese label into google translate). The other temp. sensors seem not to see that.

Now note that spike in Unit 1, and Tepco refrained from publishing any more D/W CAMS data after that event, their reports mention that the unit 1 D/W Cams is out of order, both of them the A and B channels

But are they out of order? or is there something happening in the reactor that we are not supposed to know or deduce from their data, now look at the temperature plot, on the same day 8th April there was a sudden spike coinciding with the spike of the CAMS data

I leave it for the experts to comment, was there a sudden small sub-critical event on the 8th April?
[PLAIN]http://k.min.us/in4JQ0.JPG

Could it be ... that the sudden spike of temperature on April 8th is somehow related to the nitrogen operation?

http://www.nisa.meti.go.jp/english/files/en20110504-1-2.pdf

Also by some strange coincidence this nitrogen operation might have messed with CAMS drywell?

I was not able to copy and past the Japanese sensor labels into Google Translate (pdf document does not allow copying [sure, there might be tricks..]), but awesomely enough Google Translate eats the whole pdf file and spits out translations for all sensor labels.
Wow, I am amazed... (even if the images are lost and the format gets screwed up)

http://translate.google.com/translate?js=n&prev=_t&hl=en&ie=UTF-8&layout=2&eotf=1&sl=ja&tl=en&u=http%3A%2F%2Fk.min.us%2FilskVG.pdf

The N4B sensor translates as "Water nozzle N4B (end)". But still what does N4B stand for? Just some label on some schematic that we don't have? There is also some N4C on page two of the document. (Btw, those documents are awesome! Thanks AntonL!).

 

[unlurk]

A question for the brilliant people on this thread regarding the explosion in #3.

Assuming the top of the reactor building had filled with hydrogen and that the water in SFP had dropped considerably exposing and partially melting a portion of the fuel rods, would the force of the explosion down the SPF onto the top of the water act as if it was hitting concrete thereby pushing the force of the explosion back up taking the exposed fuel rods and assemblies with it?

I also demur on the "brilliance" accusation.

But what I see missing in your hypothesis is the lack of a pressure differential between the lower parts of the SFP and the top surface.

Water is all but non compressible as were the other contents of the pond, so I can't see how an explosion above the pond would generate much force to push pond contents upward. Some force would be created when the shockwave compressed bubbles in the pond and the steel/concrete vessel was stretched and rebounded.

But that would hardly seem enough of an energy source to eject the pond contents a kilometer in the air.

TCups had a theory (early April) that went along the lines of the pond being at (something like) 211 and 3/4 degrees and the explosion adding the last 1/4 degree to make all the water in the pond turn into steam in an instant. I don't know if he still peruses this theory, but I don't think the theory has a large band of adherents in any event.

IMO, it took a large injection of energy into the lower part of the pond to achieve the explosion that we can see in the videos.

 

[AntonL]

(Btw, those documents are awesome! Thanks AntonL!).

Pleasure!, had to use a nice trick to recover them as they are pulled from the Tepco sites, Found them with google by chance, which allowed a Quick View, which then allowed me to save to googledocs, which intern then allowed me to save the pdf file to my PC

This was my first lucky find
[PLAIN]http://k.min.us/in0toI.JPG

 

[MiceAndMen]

I am not drawing any conclusions. Just pointing out that we cannot tell yet whether there was any damage or not.

On that point I agree 100%.

 

[pdObq]

The N4B sensor translates as "Water nozzle N4B (end)". But still what does N4B stand for? Just some label on some schematic that we don't have? There is also some N4C on page two of the document. (Btw, those documents are awesome! Thanks AntonL!).

Oh, google comes up with some stuff for "feedwater nozzle n4b".
These are just the first two documents with drawings and stuff, which I don't have time to digest now:

Oyster Creek: http://pbadupws.nrc.gov/docs/ML0819/ML081900084.pdf
Clinton: http://pbadupws.nrc.gov/docs/ML1103/ML110320387.pdf

Quote from the first one: "There are four feedwater nozzles in the system (N4A, N4B, N4C, and N4D)."

From the second one (p.11f) it seems that all the openings of the RPV (they call the N ones nozzle-to-shell-welds it seems) have such labels.

 

[unlurk]

On that point I agree 100%.

Unit four seems a pretty straightforward case.

Hydrogen accumulated in the building structure, mixed with oxygen and ignited.

This was not a contained explosion, the gasses could expand and compress the interior air throughout the structure before achieving enough overpressure to lift the roof slab and pop out the "blast panels."

I'm not an explosives expert, but I know that an uncontained explosive delivers less energy than one which is contained (think pipe bomb) and I can see that that fact is in play here.

The overpressure on the SFP wouldn't have been all that much.

 

[TCups]

I also demur on the "brilliance" accusation.

But what I see missing in your hypothesis is the lack of a pressure differential between the lower parts of the SFP and the top surface.

Water is all but non compressible as were the other contents of the pond, so I can't see how an explosion above the pond would generate much force to push pond contents upward. Some force would be created when the shockwave compressed bubbles in the pond and the steel/concrete vessel was stretched and rebounded.

But that would hardly seem enough of an energy source to eject the pond contents a kilometer in the air.

TCups had a theory (early April) that went along the lines of the pond being at (something like) 211 and 3/4 degrees and the explosion adding the last 1/4 degree to make all the water in the pond turn into steam in an instant. I don't know if he still peruses this theory, but I don't think the theory has a large band of adherents in any event.

IMO, it took a large injection of energy into the lower part of the pond to achieve the explosion that we can see in the videos.

Actually, the thought was that a still pool of absolutely pure water might superheat, and that an explosion venting through the fuel transfer chute, particularly one that caused a very violent agitation (atomization?) of the pre-heated water as well as initiating an accompanying, secondary hydrogen explosion in the upper floor might well result in the phase change of a sufficient volume of water to steam to result in an "eruption" from the SFP.

Water vaporizing in and around the fuel might eject some of the contents of the SFP. I can't see how a hydrogen explosion confined to the air space over the SFP could do so, however. At Unit 3, I surmise that hydrogen and superheated steam came from the primary containment, as did the initial lateral component of the explosion, into the SFP then out the SE corner of the building.

But perhaps I am just getting mixed up on conflagration vs confabulation.

 

[dh87]

Yes, this sounds odd. But hydrazine is used to prevent corrosion of steel parts in steam circuits - it removes oxygen molecules. Concentrations are very low, less than 1 ppm.

Even stranger: vitamin C is recommended as a substitute!
http://pubs.rsc.org/en/Content/Database/HAZ1307001305

I haven't read the posts beyond this one yet, but earlier posts stated that oxygen and hydrogen would recombine readily. This isn't generally true; hydrogen and oxygen don't just react. Reaction could be rapid if the oxygen is singlet oxygen (excited state). In this case ascorbic acid (Vitamin C) could help with singlet relaxation to the ground state triplet. The triplet ground state won't react readily with hydrogen. I'm not sure about hydrazine reactions.

 

[unlurk]

At Unit 3, I surmise that hydrogen and superheated steam came from the primary containment, as did the initial lateral component of the explosion, into the SFP then out the SE corner of the building.

As far as unit three goes: we are in agreement up to the point of the blast roaring through the chute and hitting the back wall of the SFP.

Where we diverge is on what happened next.

I don't see any way for the southbound hydrogen explosion to have created the pressure differential between the lower FP and its upper surface.

I don't think the hydrogen explosion had enough total energy to create the process we see in the number three explosion video anyway

The energy had to come from somewhere else and I can't buy into the idea of it coming from the latent heat of the SFP.

Tubs of hot water just don't have a reputation for blowing up like that.
This would be a first.

 

[MadderDoc]

<..>At Unit 3, I surmise that hydrogen and superheated steam came from the primary containment, as did the initial lateral component of the explosion, into the SFP then out the SE corner of the building. <..>

A blowout from the primary containment as you describe would seem to fit about every bit of strong evidence I've seen, except, I think, the ballistic expulsion of so many large and dense objects.

One can easily imagine that the fhm was blown away by such an event, although we haven't found any of it, yet, and may never do. But what about those other pieces, that went ballistic, and which we can find? I've not seen any ballistic objects that looks to me like something coming from the sfp. (see attachment for some candidate species).

I suggest we may be looking at a blowout -- like the one you describe -- but one which involved other and more than 'just' the transfer chute and the sfp.

 

[MadderDoc]

Actually, the thought was that a still pool of absolutely pure water might superheat, and that an explosion venting through the fuel transfer chute, particularly one that caused a very violent agitation (atomization?) of the pre-heated water as well as initiating an accompanying, secondary hydrogen explosion in the upper floor might well result in the phase change of a sufficient volume of water to steam to result in an "eruption" from the SFP.<..>

However this runs counter to theory and practical experience with superheated water. Yes, you can make it hiccup, but you just cannot make it flash into large amounts of water vapor. Problem is, 2000 kJ/kg is needed to vaporize water, and it has to come from somewhere. If we assume generously, that the water in the sfp had managed to superheat to 10 deg C above bp , without its boiling, the water would have a surplus energy content of only about 40 kJ/kg. There would be energy to vaporize only 2% of it.

 

[TCups]

A blowout from the primary containment as you describe would seem to fit about every bit of strong evidence I've seen, except, I think, the ballistic expulsion of so many large and dense objects.

One can easily imagine that the fhm was blown away by such an event, although we haven't found any of it, yet, and may never do. But what about those other pieces, that went ballistic, and which we can find? I've not seen any ballistic objects that looks to me like something coming from the sfp. (see attachment for some candidate species).

I suggest we may be looking at a blowout -- like the one you describe -- but one which involved other and more than 'just' the transfer chute and the sfp.

Well, first, remember that the chute gate is just a potential weak spot in the upper primary containment, particularly if a seal was already leaking. A blow out might have started at the gate and then involved some portion of one or more of the segmented "rings" that form the upper containment. Several segments are obviously engineered to be removable (certainly on the side of the equipment pool). This would seem even more likely if the force of an explosion in the primary containment were to have enough energy to lift the top plug even a small amount. Loss of the weight bearing forces, as least as I interpret the technical drawings I have seen, might substantially weaken the structural integrity of a "stacked" arrangement of semicircular segments reinforced with a concentric tongue in groove arrangement.

Second, a blow out through the fuel transfer chute might well have been into the water of the SFP, not necessarily just into the air above it.

Third, a blow out starting at or near the fuel transfer chute looks to me like it might extend into part of the upper primary containment that was below the level of the deck of the top floor, ie, into the lower confines of Bldg 3 as well as into the upper floor.

Or, lacking any other "Clues" as to what really happened, I guess that Col. Mustard did it, in the refueling bay, using a spent fuel rod assembly!

 

[MadderDoc]

<..>a blow out starting at or near the fuel transfer chute looks to me like it might extend into part of the upper primary containment that was below the level of the deck of the top floor, ie, into the lower confines of Bldg 3 as well as into the upper floor.<..>

That might explain some of the ballistic objects we find, we could be looking at bits and pieces of water heaters, heat exchangers and stuff. But we could have that too, with an eruption from somewhere else in the primary containment, Which indications do you see that the pool was involved at all?

 

[unlurk]

a blow out through the fuel transfer chute might well have been into the water of the SFP, not necessarily just into the air above it.

I guess that Col. Mustard did it, in the refueling bay, using a spent fuel rod assembly!

How do you envision a blast coming from the chute "under the water in the SFP"?

Are you suggesting that the fuel transfer chute was full of water?
That's a difficult assertion, in the face of the premise that the source of the hydrogen was the drywell. Hydrogen is lighter than water.

In any event, the tops of the rods were below the level of the transfer chute.

And fuel rods from the SFP of unit three are currently scattered about the Fukushima one site. I hope we are in agreement on that.Col. Mustard? It seems as though you will grasp at any straw to avoid seeing the obvious.Nobody is served by covering up the real source of the accident at unit three.
Least of all the nuclear power industry, if that is who you are trying to protect.Edit: I notice I used the term "under the water in the SFP" when you actually said "into the water."

However my point still stands unless you meant downward when you said "into the water", into appeared to me to be meant to suggest that the hydrogen blast got under the water.

Correct me if I was wrong.

 

[Jorge Stolfi]

One can easily imagine that the fhm was blown away by such an event, although we haven't found any of it

The FHM can travel only between the SFP and the reactor refueling pool. Is there any chance that it may have been under the crane, and was partly squashed flat, partly pushed down into the refueling pool, when the latter fell on top of it?

The FHM looks big and bulky, but perhaps it is relatively light and fragile, as it does not have to carry heavy loads. The conspicuous "hockey sticks" on the east side, for example, seem to be hollow cable counduits (those in the #4 FHM were bent by the explosion, which hardly damaged other flimsier parts of it.) The crane, on the other hand ...

Also the aerial photos from the West show that the service floor slab was damaged and the part under the crane is sagging.

This theory would be less implausible if the refueling pool was open (without the concrete shield plugs) at the time of the explosion. Any chance of this being the case?

 

[TCups]

That might explain some of the ballistic objects we find, we could be looking at bits and pieces of water heaters, heat exchangers and stuff. But we could have that too, with an eruption from somewhere else in the primary containment, Which indications do you see that the pool was involved at all?

Well, something . . .
1) started with a fireball shooting out of the southeast corner of Bldg 3.
2) tore a big hole directly over the SFP
3) moved the FHM somewhere else
4) caused a large, dense column of steam (I think) to erupt, Vesuvially, straight upward
5) spread a bunch of radioactive debris hither and yon
6) left the top plug of the primary containment in place, under the large overhead crane
7) and left the RPV more or less intact, at least initially

Connecting the dots, the SFP3 is at the top of my list, but something had to add a substantial amount of energy to the mix. I doubt an unconfined "sudden criticality", based on comments from a few trusted sources on this board, and, absent any large quantities of really nasty, really hot, high level radioactive debris that one might expect from the explosion and expulsion of the fuel rod assemblies themselves. (One piece of 900 mSv/hr concrete ≠ exploded fuel rods). But who knows for sure? I may be just another Bozo on the bus. . .

 

[unlurk]

<b>Source of energy for the Number three blast</b>

If the rods in the FP were capable of criticality inside a reactor, why would they not be capable of criticality in the SFP?

A rather powerful explosion had just occurred adjacent to and directly above the fuel pond, in fact the leading edge of this blast had collided with the part of the fuel pond which is above the rods in the pool and would have potentially, or very likely, sent an aysemetric shock wave down into the pool thereby distorting and bending the rods and maybe even the contents of the rods.

In this turmoil of uranium rods and pieces of rods swirling around in the spf why couldn't a mass of them come into proximity with each other for a half a picosecond in a configuration which would support criticality? They had plenty of water for a moderator.

The critical mass would then blow itself apart nearly instantly (maybe in a microsecond) but in the process would release enough joules of heat to create a steam explosion and send the (preheated) contents of the fuel pond out the only escape route it had: skyward.

This will not remain a mystery forever, we can be sure of that.

To say this couldn't happen is to deny the history of criticality accidents.

 

[MiceAndMen]

Col. Mustard? It seems as though you will grasp at any straw to avoid seeing the obvious.

Nobody is served by covering up the real source of the accident at unit three.
Least of all the nuclear power industry, if that is who you are trying to protect.

TCups's theory is not one I subscribe to, but I think you misunderstand him here. You would do well to go back through the thread and see for yourself what that theory is. He has been remarkably consistent with it and if you had bothered to read even a handful of his posts about it you wouldn't be accusing him of protecting anyone.

 

[TCups]

If the rods in the FP were capable of criticality inside a reactor, why would they not be capable of criticality in the SFP?

A rather powerful explosion had just occurred adjacent to and directly above the fuel pond, in fact the leading edge of this blast had collided with the part of the fuel pond which is above the rods in the pool and would have potentially, or very likely, sent an aysemetric shock wave down into the pool thereby distorting and bending the rods and maybe even the contents of the rods.

In this turmoil of uranium rods and pieces of rods swirling around in the spf why couldn't a mass of them come into proximity with each other for a half a picosecond in a configuration which would support criticality? They had plenty of water for a moderator.

The critical mass would then blow itself apart nearly instantly (maybe in a microsecond) but in the process would release enough joules of heat to create a steam explosion and send the (preheated) contents of the fuel pond out the only escape route it had: skyward.

This will not remain a mystery forever, we can be sure of that.

To say this couldn't happen is to deny the history of criticality accidents.

Maybe it is an empiric trust in the nuclear energy industry sadly misplaced, but, I must believe that "criticality" inside a reactor core, using uranium fuel rods enriched to 3% requires a pretty carefully planned geometric arrangement of fuel rod assemblies, control rods and moderators that doesn't happen by chance.

This accident is not a scenario of letting two hemispheres of pure plutonium get too close, or pouring concentrated uranium salts in liquid solution from several smaller containers into a single large container too quickly.

I just simply cannot bring myself to imagine the conceptual failure to engineer and store spent or unspent fuel rods in any arrangement inside SFP racks, or anywhere else outside of a reactor core that would allow even the remote possibility of criticality to occur.

But perhaps we are destined to see many strange things in Fukushima now that George Bailey San never existed.

And fuel rods from the SFP of unit three are currently scattered about the Fukushima one site. I hope we are in agreement on that.

!?? Has that indeed been confirmed? Did I miss it? Gulp.

 

[unlurk]

I just simply cannot bring myself to imagine the conceptual failure to engineer and store spent or unspent fuel rods in any arrangement inside SFP racks, or anywhere else outside of a reactor core that would allow even the remote possibility of criticality to occur.

That sounds almost "faith based" IMO.
Faith based reasoning rolls off me like water off a ducks back.

!?? Has that indeed been confirmed? Did I miss it? Gulp.

Post # 3319 at page 208 was never rebutted that I know of.
https://www.physicsforums.com/showthread.php?t=480200&page=208


TCups, You have added the search for answers which would be all but lacking here if not for you. I don't mean to be critical of you personally.

But I think you are fighting somebody else's battle here. So you get to take the slings and arrows of righteous indignation which follow.

Sorry about that.

 

[Dmytry]

Maybe it is an empiric trust in the nuclear energy industry sadly misplaced, but, I must believe that "criticality" inside a reactor core, using uranium fuel rods enriched to 3% requires a pretty carefully planned geometric arrangement of fuel rod assemblies, control rods and moderators that doesn't happen by chance.

BS. It is closer to 5% for unspent rods in BWR, and it used to happen for 2..3% naturally a while back:
http://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor

This accident is not a scenario of letting two hemispheres of pure plutonium get too close, or pouring concentrated uranium salts in liquid solution from several smaller containers into a single large container too quickly.

I just simply cannot bring myself to imagine the conceptual failure to engineer and store spent or unspent fuel rods in any arrangement inside SFP racks, or anywhere else outside of a reactor core that would allow even the remote possibility of criticality to occur.

Google 'boral'. Compressed mix of boron carbide and aluminium dust.

I think you have some sort of severe misunderstanding as of why the very careful geometry is necessary. It is necessary to sustain the controllable criticality over a wide range of uranium concentrations (from fresh to old fuel), and furthermore burn up the fuel equally. Also, the xe-135 is produced during reactor operation, with a good lag. xe-135 is a neutron poison and it limits lifespan of fuel. But after you take the spent fuel out, and xe-135 decays, the spent fuel has some criticality margin again.

Really, the thought that the criticality is something hard to achieve is how most of the criticality accidents have happened (the mundane ones, not dramatically stupid like Slotin's)

 

[ascot317]

And fuel rods from the SFP of unit three are currently scattered about the Fukushima one site. I hope we are in agreement on that.

They must be pretty cold then, they're not showing up on IR. I yet have to see evidence for that claim. We've asked this before, were is it? I've been actively looking for it, but it is frustrating to see claims of such but not finding evidence supporting it.


Regarding criticality in the #3SFP, well, #4 blew up without any working reactor. Still, the SFP looks fairly undamaged inside. #3 had a hot reactor in addition to a SFP. #3 was very likely leaking hydrogen into the containment, in addition to the SFP doing the same.

It's even possible that there were numerous hydrogen leaks/sources in the whole building:

the SFP, the drywell-head, the SGTS/venting system. It's known that the containment leaks under high pressure, so do the venting systems. There were probably many cavities filled with hydrogen (even the venting stack pipes were affected). I still believe this was just another hydrogen explosion. Just a very powerful one, possibly with more than one room affected.

 

[RealWing]

Some interesting facts about dense packing and criticality in this document. It also discusses fuel cooling as the water level drops.

Reducing the Hazards from Stored Spent Power-Reactor Fuel in the United States http://www.princeton.edu/sgs/publications/sgs/pdf/11_1Alvarez.pdf

Because of the unavailability of off-site storage for spent power-reactor fuel, the NRC
has allowed high-density storage of spent fuel in pools originally designed to hold much
smaller inventories. As a result, virtually all U.S. spent-fuel pools have been re-racked
to hold spent-fuel assemblies at densities that approach those in reactor cores. In order
to prevent the spent fuel from going critical, the fuel assemblies are partitioned off from
each other in metal boxes whose walls contain neutron-absorbing boron. It has been
known for more than two decades that, in case of a loss of water in the pool, convective
air cooling would be relatively ineffective in such a “dense-packed” pool. Spent fuel
recently discharged from a reactor could heat up relatively rapidly to temperatures at
which the zircaloy fuel cladding could catch fire and the fuel’s volatile fission products, including 30-year half-life137 Cs, would be released. The fire could well spread to older spent fuel. The long-term land-contamination consequences of such an event could be significantly worse than those from Chernobyl.

Page 24
Figure 8 shows the value of the neutron multiplication factor keff in an infinite
square array of 4.4% enriched fuel at various burnups as a function of the spacing
between the rod centers (the array “pitch”) in a pool of unborated water.
It will be seen that, for burnups of less than 50 percent, the open array is critical
at a pitch of 2.6 cm and that the neutron multiplication factor increases as the
pitch decreases to about 1.6 cm.

 

[TCups]

That sounds almost "faith based" IMO.

TCups, You have added the search for answers which would be all but lacking here if not for you. I don't mean to be critical of you personally.

But I think you are fighting somebody else's battle here. So you get to take the slings and arrows of righteous indignation which follow.

Sorry about that.

The only "battle" I am waging is in my own mind.

The only criticality (or lack thereof) of which I can be sure lies is in my thought processes.

Did "sudden criticality" occur in SFP3? Maybe, I don't know, but

Neutron source ≠ fuel rod.

High level radioactive debris ≠ fuel rod.

A small, exposed fragment of a damaged fuel rod ≠ irrefutable evidence of criticality

Did very small fragments of fuel rods get scattered for up to a mile? Maybe, I don't know.

If a substantial piece of a fuel rod blew out of SFP3, it almost certainly did not end up 1 mile away, IMO.

Per private correspondence with those much more knowledgeable than I, it appears that an exposed spent fuel rod would heat rapidly in air and be easily visible on thermal images.

Have I seen a definitive picture of a substantial piece of an exposed fuel rod, either by standard or thermal imagery, outside of the SFP or core of any reactor in any of the preceding 6347 posts? -- I don't think so.

Might there be some other explanation besides "sudden criticality" that powered the explosion(s) at Bldg 3 and SFP 3? Maybe, I don't know.

I do know that it is bedtime for Bozo, though. I will sleep on it.
PS: Wake me up if Bldg 4 falls over, please.