Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[M. Bachmeier]

How does Iodine get into tap water so quickly? Most drinking water system facilities have been shut down by the earthquake and Tsunami. Also, most domestic drinking water supplies are a relatively closed system with carbon adsorbers, which would filter out the Iodine. Sounds fishy to me. Everyone probably went to bottled water following the Tsunami and destruction.

It makes you wonder if the samples were contaminated during testing?

 

[Reno Deano]

The helicopter fly over spent a lot of time looking at this debris field and at something on the top of this building. Curious.

What sort of blast might scatter spent fuel rods out of a SFP? One venting through the channel between the SFP and the reactor containment?

Astronuc: I hope you make it -- God speed and take care. Be sure to take a laptop and check in with us. Anyone else from your team likely to make the trip?

Since the blast was not likely below the spent fuel pool (pool structure would mitigate the blast force), the spent fuel elements due to their weight would not be ejected from the racks which are a tight fix due to seismic considerations.

 

[MadRocketSci2]

So you're going to take a bunch of half-starved, injured, freezing refugees and tell them not to drink the water because there is a remote possibility that they might get cancer someday if the levels of radioactives detected were 300 times what they are? This is the kind of insanity about radiation that is going to get more people hurt than the disaster ever will.

There might be other good reasons not to drink the water (quite a lot of things broke during the quake and the tsunami - there's probably all sorts of chemical stuff washing around. Radiation though?

1 Bq is 1 decay per second. I wouldn't be surprised to see 1 Bq/kg in natural sources - we have radon in basements on the east coast. There are 10^26 atoms in a typical kg of material. 1 Bq is nothing. Your body has 4kBq going on in it all the time.

 

[swimmer]

So you're going to take a bunch of half-starved, injured, freezing refugees and tell them not to drink the water because there is a remote possibility that they might get cancer someday if the levels of radioactives detected were 300 times what they are? This is the kind of insanity about radiation that is going to get more people hurt than the disaster ever will.

There might be other good reasons not to drink the water (quite a lot of things broke during the quake and the tsunami - there's probably all sorts of chemical stuff washing around. Radiation though?

1 Bq is 1 decay per second. I wouldn't be surprised to see 1 Bq/kg in natural sources - we have radon in basements on the east coast. There are 10^26 atoms in a typical kg of material. 1 Bq is nothing. Your body has 4kBq going on in it all the time.

Regarding tap water and I-131, this is the equation that works for me:

Reading up on science + common sense + friends in Tokyo & Japan + given a choice = avoid tap water.

 

[Maxion]

Regarding tap water and I-131, this is the equation that works for me:

Reading up on science + common sense + friends in Tokyo & Japan + given a choice = avoid tap water.

I would ask for a refund of my education and common sense if that is your opinion. I-131 is absorbed by the thyroid, if there are large levels of I-131 running around the common thing to do is to fill your thyroid with non-radioactive iodine which prohibits the uptake of radioactive iodine. Besides I-131 has a half-life of roughly 8 days so it is quite quickly gone.

Irrational fear of radiation is something that will really hurt our civilization.

 

[TCups]

DEBUNK THE UNIT 3 BLAST SCENARIO PLEASE

Since the blast was not likely below the spent fuel pool (pool structure would mitigate the blast force), the spent fuel elements due to their weight would not be ejected from the racks which are a tight fix due to seismic considerations.

OK, understand, but I am not sure that the blast force can be mitigated as easily.

Looking for those more learned than me to debunk this hypothesis of the blast mechanism at Unit 3, which I have put together from what I have gleaned at this website.

SCHEMATIC:

(1) An overheating reactor core results in damaged fuel rods, oxidization, and reaction of steam + zirconium accumulating in the reactor containment vessel. Due to increased pressure and heat in the reactor vessel, hydrogen gas is vented into the primary containment vessel, but that increased pressure eventually compromises the seals at the drywell head.

see: http://allthingsnuclear.org/post/3940804083/possible-cause-of-reactor-building-explosions

(2) Hydrogen gas under pressure can now leak into the refueling cavity, and perhaps into the upper building structure either around the concrete shield plug or the gate between the refueling cavity and the spent fuel pool.

(3) The seals on the gate to the spent fuel pool are pneumatic and pressure in the seals is maintained by electric pump. If the electricity fails, the seals could fail allowing both water from the SFP to leak into the refueling cavity, and H2 gas to leak out.

see: http://allthingsnuclear.org/post/3964225685/possible-source-of-leaks-at-spent-fuel-pools-at

(4) An explosion arising from the pressurized hydrogen + steam within the primary containment, but leaking into the upper building, might find the path of least resistance as a blow-out through the gate with damaged seals and chute, and finally, into the SFP. The SPF, would tend to direct a large portion of the blast from the containment upward, and could potentially scatter high level radioactive debris -- if not all of the fuel rods, then perhaps fragments of the damaged fuel rods, many of which may be visible within the damaged upper portion of unit 3, in the area of the blast near the SFP, as seen on the helicopter fly by. Additional hydrogen gas accumulated in the upper building structure would also explode, blowing out the walls of the upper building -- a 1-2 punch. Steam from the primary reactor containment could now vent through the blast defect in the transfer chute.

see:
http://1.bp.blogspot.com/-5gGV59tdlt0/TX2J7O4F1rI/AAAAAAAABkM/FIfqa-RMJNQ/s400/reactor3.JPG

 

[Maxion]

(2) Hydrogen gas under pressure can now leak into the refueling cavity, and perhaps into the upper building structure either around the concrete shield plug or the gate between the refueling cavity and the spent fuel pool.

(3) The seals on the gate to the spent fuel pool are pneumatic and pressure in the seals is maintained by electric pump. If the electricity fails, the seals could fail allowing both water from the SFP to leak into the refueling cavity, and H2 gas to leak out.

see: http://allthingsnuclear.org/post/3964225685/possible-source-of-leaks-at-spent-fuel-pools-at

(4) An explosion arising from the pressurized hydrogen + steam within the primary containment, but leaking into the upper building, might find the path of least resistance as a blow-out through the gate with damaged seals and chute, and finally, into the SFP. The SPF, would tend to direct a large portion of the blast from the containment upward, and could potentially scatter high level radioactive debris -- if not all of the fuel rods, then perhaps fragments of the damaged fuel rods, many of which may be visible in the area of the blast in Unit 3 as seen on the helicopter fly by. Additional hydrogen gas accumulated in the upper building structure would also explode, blowing out the walls of the upper building -- a 1-2 punch. Steam from the primary reactor containment could now vent through the blast defect in the transfer chute.

see:
http://1.bp.blogspot.com/-5gGV59tdlt0/TX2J7O4F1rI/AAAAAAAABkM/FIfqa-RMJNQ/s400/reactor3.JPG

IANANE (I am not a nuclear engineer) but isn't the SFP, canal and drywell head submerged under water constantly?

If that is the casen for the hydrogen to explode it would first have to seep through the concrete plug and into the containment building. Then it would rise to the roof and the highest concentration of hydrogen would be at roof level, not floor.

Here's a cross section of a BWR MK 1 design (I think?) posted earlier. ( http://media.tumblr.com/tumblr_li9czl6f4v1qbnrqd.jpg )

 

[TCups]

IANANE (I am not a nuclear engineer) but isn't the SFP, canal and drywell head submerged under water constantly?

Unless a portion of the water is boiled off or leaks off or both. The transfer chute is not as deep as the entire well, though.

If that is the casen for the hydrogen to explode it would first have to seep through the concrete plug and into the containment building. Then it would rise to the roof and the highest concentration of hydrogen would be at roof level, not floor.

Unless, of course, the explosion ORIGINATED in the primary containment, where the pressurized hydrogen gas and most of the really hot stuff that might cause an explosion are most likely to be. The unpressurized hydrogen gas that had leaked into the upper building ignited as a secondary explosion after the high-pressure explosion below.

Here's a cross section of a BWR MK 1 design (I think?) posted earlier. ( http://media.tumblr.com/tumblr_li9czl6f4v1qbnrqd.jpg )

I will study it and comment if appropriate. I hope IANANE means "I am not a network engineer" and wasn't intended to be INNANE. I am not a network engineer, either.

Addendum: sorry, I initially posted the wrong pic under "SCHEMATIC" -- I apparently made that correction while you were typing. I have annotated the same diagram you supplied.

Give me your best shot. I am just struggling to figure this out and can use any feedback or alternative hypothesis.

 

[AntonL]

What sort of blast might scatter spent fuel rods out of a SFP? One venting through the channel between the SFP and the reactor containment?

I have been toying with this problem for some time. I tried to imagine the explosion dynamics at the explosion centre and the SPF being at the explosion centre. I put my ideas here for test and discussion.

Idea 1:
a. Let's assume a hydrogen explosion, H2 and O2 combine generate enormous heat and water, the blast shock wave spreads out accelerating the atmosphere away from the explosion centre, thus leaving a vacuum
b. The explosion is immediately followed by an implosion at the explosion centre.
c. Now assume a boiling SFP, and if the vacuum does exist the water in the SFP will momentary super-boil as during the low pressure phase of the explosion huge amounts of steam generate where it is hottest, right by the fuel, ejecting or propelling water fuel rods into the air.

Idea 2:
Assume water is boiling in SFP. Its volume is a combination of liquid volume and steam volume. The steam bubbles in the water allow the water to be compressed like a sponge and the explosion will compress the water, a shock wave is established in the pool and the re-condensing of the steam in suspension due to the higher pressure causing the water to collapse. This shock wave soon will have the opposite effect and a decompression will take place which will stretch or lower the pressure of the water and water will again expand as the steam bubbles are produced. Once the water is accelerated vertically this movement is sustained by the water being immediately replaced by steam. Again super-boiling could take place causing the ejection as in c above.

Idea 3: combination of 1 and 2

Above might describe what TCups calls "what sort of blast"

I do not know if this was discussed earlier, Look at the video of the explosion of reactor 1
http://www.youtube.com/watch?v=TZ6lurStTvU&feature=related"
The very first frames 0 to 2 seconds of the video and repeated later at 40 to 42 seconds. At the beginning of explosion a vertical column of I do not know what is rising at great speed and then quickly disappearing into nothing. Can someone please explain this vertical column that then disappears. What makes it even more intriguing from satellite pictures it seems that the roof of reactor 1 has collapsed as one piece as no visible roof or building structure is visible. Now if you continue watching the video you will note something black/dark lifting in the explosion cloud and then falling back to ground. If that something dark is the roof and then lands right back from where it came from I conclude that it got sucked back lending weight to idea 1 above.

 

[TCups]

I have been toying with this problem for some time. I tried to imagine the explosion dynamics at the explosion centre and the SPF being at the explosion centre. I put my ideas here for test and discussion.

Above might describe what TCups calls "what sort of blast"

I do not know if this was discussed earlier, Look at the video of the explosion of reactor 1
http://www.youtube.com/watch?v=TZ6lurStTvU&feature=related"
The very first frames 0 to 2 seconds of the video and repeated later at 40 to 42 seconds. At the beginning of explosion a vertical column of I do not know what is rising at great speed and then quickly disappearing into nothing. Can someone please explain this vertical column that then disappears. What makes it even more intriguing from satellite pictures it seems that the roof of reactor 1 has collapsed as one piece as no visible roof or building structure is visible. Now if you continue watching the video you will note something black/dark lifting in the explosion cloud and then falling back to ground. If that something dark is the roof and then lands right back from where it came from I conclude that it got sucked back lending weight to idea 1 above.

The 0-2 sec is a shock wave, perhaps a reflected shock wave, traveling upward, ahead of the debris and smoke. The force of the actual explosion at unit one blasts most of the building outward, consistent with origin of the explosion from within the top floor. There isn't much in the way of concrete and dust to blast skyward in that scenario.

 

[TCups]

UNIT 3 EXPLOSION

Video here:


Unlike the explosion at Unit 1, the Unit 3 explosion starts with a fireball blasting upward and to the right -- not with the whole top floor of the building blowing outward.

. . . which fits with my proposed mechanism.

 

[jensjakob]

TCups - I think that we together are hitting bulls eye.

 

[TCups]

TCups - I think that we together are hitting bulls eye.

Well, there does definitely seem to be some part of the bull involved -- not yet sure whether it is the eye or not. But until someone proves me wrong, my working hypotheis is that it was hydrogen in the reactor containment that exploded first, probably venting upward and outward through the transfer chute then the SFP. And I believe there will be many bits of very nasty stuff blasted out as a consequence.

 

[Maxion]

Well, there does definitely seem to be some part of the bull involved -- not yet sure whether it is the eye or not. But until someone proves me wrong, my working hypotheis is that it was hydrogen in the reactor containment that exploded first, probably venting upward and outward through the transfer chute then the SFP. And I believe there will be many bits of very nasty stuff blasted out as a consequence.

Going back to my limited knowledge of BWR reactors, the primary containment is supposed to be filled with an internt gas and therefor hydrogen in the primary containment shouldn't be able to explode.

IMO if the explosion didn't occur in the containment building then it occurred in the refueling cavity if it wasn't under water.

 

[AntonL]

DEBUNK THE UNIT 3 BLAST SCENARIO PLEASESCHEMATIC:

(2) Hydrogen gas under pressure can now leak into the refueling cavity, and perhaps into the upper building structure either around the concrete shield plug or the gate between the refueling cavity and the spent fuel pool.

I would imagine that the concrete plugs are not airtight nor is it circular as we would imagine a plug to be. Concrete has a specific gravity of 2.5 I would imagine the plug to be an array of concrete beams sized to be of manageable weight for the overhead crane to handle. They would be impossible to be made air tight. They just provide a floor and possibly radiation shielding. Primary containment ends with the steel dome labelled Steel Containment Vessel

[PLAIN]http://nei.cachefly.net/static/images/BWR_illustration.jpg

 

[curious11]

Fascinating analysis and discussions on here.
The containment explosion hypothesis seems a likely explanation for the multiple explosions heard during the reactor 3 event. ie pop 1 being the pressure vessel, pop2 being the primary containment, and then pop 3 being the unpressurised hydrogen in the roof void. Although I would not have expected such large durations between each pop, and there are no visible signs of 3 independent explosions.

To add another area of curiousity, has anyone considered what the grey area that appears to have emanated from reactor 3?

http://patrick.reformstudios.com/p.jpg

 

[TCups]

I would imagine that the concrete plugs are not airtight nor is it circular as we would imagine a plug to be. Concrete has a specific gravity of 2.5 I would imagine the plug to be an array of concrete beams sized to be of manageable weight for the overhead crane to handle.

[PLAIN]http://nei.cachefly.net/static/images/BWR_illustration.jpg[/QUOTE]

Yes, in one of the pictures, the plug looks octagonal. So perhaps a portion of the plug blew out.

[PLAIN]http://i306.photobucket.com/albums/nn270/tcups/5596b43d.jpg

Still, the primary explosion is extremely powerful, and it is upward and to the right, consistent with the visible damage in the close ups. Hydrogen is lighter than any other inert gas and would rise to the top. The seal of the transfer chute (and therefore the primary containment) may have leaked. And did I read that the oxidation reaction with zirconium and steam produced hydrogen and oxygen? Someone correct me if I am wrong please.

 

[Maxion]

Y
The seal of the transfer chute (and therefore the primary containment) may have leaked. And did I read that the oxidation reaction with zirconium and steam produced hydrogen and oxygen? Someone correct me if I am wrong please.

No, the seal of the primary containment is the cap of the steel containment vessel. There should be no pressure proof anything above that. I'm not sure where you're getting this seal of the transfer chute from, that seal is most likely no more secure than the concrete plug.

 

[jensjakob]

@TCups:
Hints at Drywell Head leaks:
http://www.nrc.gov/reading-rm/doc-collections/gen-comm/bulletins/1978/bl78009.html

 

[jensjakob]

Quote: "Results indicate failure of the drywell head seals due to the extremely hot atmospheric conditions extant in the drywell"

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V4D-4810V35-3B&_user=10&_coverDate=08%2F31%2F1990&_rdoc=1&_fmt=high&_orig=gateway&_origin=gateway&_sort=d&_docanchor=&view=c&_searchStrId=1686158130&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=65af6e45103124c71a4ec4249f9e5577&searchtype=a

 

[jensjakob]

Containment Integrity study:
http://www.nrc.gov/reading-rm/doc-collections/nuregs/contract/cr6906/cr6906.pdf

 

[AntonL]

Fascinating analysis and discussions on here.
The containment explosion hypothesis seems a likely explanation for the multiple explosions heard during the reactor 3 event. ie pop 1 being the pressure vessel, pop2 being the primary containment, and then pop 3 being the unpressurised hydrogen in the roof void. Although I would not have expected such large durations between each pop, and there are no visible signs of 3 independent explosions.

echos - not three explosions

To add another area of curiousity, has anyone considered what the grey area that appears to have emanated from reactor 3?

Side of cut away hill plastered with debris

And did I read that the oxidation reaction with zirconium and steam produced hydrogen and oxygen? Someone correct me if I am wrong please.

Yes correct - hot zirconium and steam will extract the oxygen from the H20 releasing the H2

Hydrogen for Unit 1 and 3 produced in reactor and leaked into the building.

Unit 4 Hydrogen generation is a mystery to me as TEPCO always claimed that SFP had water in it so how did fuel rods get partly exposed to generate steam and heat to allow the oxyidizing reaction of zirconium to and what caused a self extinguishing fire twice in unit 4.

 

[Maxion]

Unit 4 Hydrogen generation is a mystery to me as TEPCO always claimed that SFP had water in it so how did fuel rods get partly exposed to generate steam and heat to allow the oxyidizing reaction of zirconium to and what caused a self extinguishing fire twice in unit 4.

There is a plausible explanation to unit four IMO. TEPCO claimed the SPF had water in it. Let's say it does. Unit four was under maintenance during the disaster and the fuel had been removed from the reactor to the SPF. Since I am not at all familiar to the procedures taken during maintenance or refueling of a reactor this is speculation but could there have been fuel rods in the equipment storage pool? IF there was fuelrods there then that might explain fuel rods oxidizing with there still being water covering the fuel rods in the SPF ;)

 

[jensjakob]

Good point:
http://lewis.armscontrolwonk.com/archive/3640/fukushima-reactor

Immediate after the shutdown,there still needed for quite a while to be removed residual heat compared to 100% power production.

Remember, even though that after shutdown residual powergeneration went to 7% - there still was the heat a few minutes ago from 100% power generation (or what ever level they were blasting along at)

 

[jensjakob]

"Drywell head is predicted to unseat at 27 psig" (page 5, upper part)
http://www.osti.gov/bridge/purl.cov...F5E975EF06A9A903D0D15E6?purl=/5630475-EX87x5/

Holy cow - that is about just a FEW BAR!

"Just a few square inches are enough to relieve pressure"
"Due to the large surface of the drywell head, leaks are easy"

If that is true - then there is a SERIOUS flaw in the BWR 1 (and otherrrs?) design - and a quite plausible documentation for TCups theory.

That is quite bad - so I kindly request you to do your best to dis-prove this theory, we need to see if we have hit bulls-eye.

Found also this detail diagram of drywell head fastening:
http://www.ansn.org/Documents/Training/PSA%20Level%202%20(Probabilistic%20Safety%20Assessment)/M5%20%20Containment%20Perform.ppt#292,17,Example: BWR Drywell Head Seal

 

[M. Bachmeier]

echos - not three explosions


Side of cut away hill plastered with debris



Yes correct - hot zirconium and steam will extract the oxygen from the H20 releasing the H2

Hydrogen for Unit 1 and 3 produced in reactor and leaked into the building.

Unit 4 Hydrogen generation is a mystery to me as TEPCO always claimed that SFP had water in it so how did fuel rods get partly exposed to generate steam and heat to allow the oxyidizing reaction of zirconium to and what caused a self extinguishing fire twice in unit 4.

In an interview with an employee working in unit 4, he described water (in large quantities) splashing out of the spent fuel containment pool at the time of the earthquake (said he was covered with it and thought he was going to die). Also, several pieces of equipment that were brought into the building (for inspection purposes) were knocked to the ground. There was definitely water lost at the time of the quake.

 

[|Fred]

Hey,
I'll concede that I'm out of my league in here, None the less couldn't be one way of looking at the issue to look at the kind of radioactivity (isotopes) we are dealing with ?

If I'm not mistaken, the radioactivity that we measure at 30Km did not arrive by it self and seems to be increasing. In order for those fission material to travel they need to fly hence to be Gaseous / Soluble in watter => Steam / Metal ionised => Smoke

We are seeing vapor for the past days
We are seeing increasing radioactivity in the 30km zone
We are seeing iodine radiation in the 30km zone
Iodine isotope is water soluble / Vapor "movable"
There has been no logged venting since the 15th
Iodine radioactive isotope has a small half live

Doesn't it make sens that the idodine that they are getting comes from the reactor 3 core rather than the spent fuel pool ? And since they did not vent R3 that it comes from the steam that is said to be SFP related?

 

[jensjakob]

Fred, interesting chain of action analysis.

If you're correct - we're facing a melting core in #3, that is venting to the outside :-(

I hope you're wrong - for the sake of the environment.

One hole I can see, the theory would need a leak from the reactor pressure vessel to the containment bulding.

 

[Maxion]

Doesn't it make sens that the idodine that they are getting comes from the reactor 3 core rather than the spent fuel pool ? And since they did not vent R3 that it comes from the steam that is said to be SFP related?

Why would it have to come from the core rather than the SFP? The same rods are in the pools and according to Tepco the ponds have most likely been empty at some point in time. Remember Occam's razor. A simple theory is most likely the correct one, unless we have proof that it is more complex.

 

[Bez999]

@jensjakob: one would assume they continuously vent from the reactor vessel to the dry well, as that is in fact the cooling procedure going on with sea water. This venting ends up through the wet well also, as per the design. What is not according to design is any leaking of the containment through the dry well cap, a problem earlier encountered in this design (see report quoted above). In this case the seal of that cap may well have been further breached as per tcup's theory, and this would accord with the sort of steam plume we see above the no3 building, again see tcup's argument. So, while the officials say that no venting to the outside was necessary because the pressure dropped by itself, it may be that the containment is venting continuously anyway, which would also tie in with the ongoing radiation readings, and especially the presence of soluble iodine isotopes, which could presumably be transferred effectively through steam and water vapor.

 

[|Fred]

The one in the Core had one week (1/2 life) of decay while the one in the pool Have a lot more. Venting has been stopped for five days. Iodine radioactivity increase more than during wenting. It does make sens to get more with a less radioactive source?

 

[havemercy]

Hello to all,

I am a new visitor of this site and, first of all, i want to apologie for my poor level of english.

Here in switzerland and France we are a little lost with the F. situation and in particular regarding the information confirming or not the formation of a corium and in which reactor.

Some are saying, from the TMI situation, that coriums are actualy presents in reactor 1, 2 and 3, that they are going through the ciment structure of the reactors (probably 1 meter per 24 hour) and that the big threat is now the contact of it with groundwater in the soil.

We also wander what occurred to the main used fuell vessel that should contain a lot of material. Many thanks in advance.

havemercy

 

[jensjakob]

More studies on BWR Mark1 failures:
http://www.osti.gov/bridge/product.biblio.jsp?query_id=1&page=0&osti_id=6980202&Row=1

A very nice source for many good factual background documents:
http://sustainableenergytoday.blogspot.com/2011/03/post-31-bwr-severe-accidents-primer.html

 

[TCups]

Fascinating analysis and discussions on here.
The containment explosion hypothesis seems a likely explanation for the multiple explosions heard during the reactor 3 event. ie pop 1 being the pressure vessel, pop2 being the primary containment, and then pop 3 being the unpressurised hydrogen in the roof void. Although I would not have expected such large durations between each pop, and there are no visible signs of 3 independent explosions.

To add another area of curiousity, has anyone considered what the grey area that appears to have emanated from reactor 3?

http://patrick.reformstudios.com/p.jpg

The additional "booms" are very likely echoes. The gray debris result from two of the side panels of building three blowing out, striking the smaller building behind, and scattering debris on the steep slope of the berm, behind. I think I posted that earlier when we were looking at the holes in the top of the steam turbine buildings.

 

[fusefiz]

If water has been covering the fuel in the reactor 4 pool, what could have generated the hydrogen?

I have been reading this thread for most of the week and wondering myself. Today I discovered the French analysis, which is the most coherent treatment I have found. I have almost no time now, so I will just briefly pass on a few of their conclusions. Sometime during the next 24 hours I hope to write more.

The French conclude that the reactor 4 pool has been covered by water. They believe the explosion was due to hydrogen which was created in the fuel pool by radiolysis. This hydrogen and oxygen could accumulate in the building since the ventilation equipment that usually handles this problem was not powered.

They calculate 3MW of heat generation in this pool, which should be boiling or start to boil soon. If this water is boiled off and not replenished, they expect this fuel to burn, melt into corium, and eat through the pool bottom, accompanied by a MAJOR release of radiation.

The French analysis also concludes that the "biological shield" (i.e., the concrete plug) is missing in reactor 3 (but still present in reactor 1, where the roof has apparently been completely blown away leaving a clear view of the refueling deck). As I understand it, under this shield there would still be the drywall head, and under that would be the cap on the reactor pressure vessel.

From an analysis of the damage in the reactor 3 building, the French suggest that the spent fuel pool may have suffered major structural damage which, in the worst case, would leave only 1 meter of water over the top of the fuel rods (this damage would be in addition to any possible leaks).

So suppose there is reduced shielding over the reactor 3, and possibly reduced shielding over its spent fuel pool. Could this explain the strong radiation detected by the helicopters over the reactors? I.e., this would be gamma radiation from reactor 3 and possibly its pool, not from the reactor 4 pool. If that is the case, I believe some of this gamma radiation would be also be reflected down to Earth around the reactor by the damaged structural beams. And if this is the case, reactor 3 will be difficult to deal with and eventually clean up.

Here is a link to an English article which communicates a bit of their analysis,
| http://blogs.wsj.com/washwire/2011/03/17/did-nrcs-jaczko-misspeak/

The French news releases can be found here (1 or more per day, PDF files):
| http://www.irsn.fr/FR/Actualites_presse/Actualites/Pages/actualite.aspx

The following press release contains, at the end, a photo annotated with some of their conclusions (all in French, their English version of this website does not have translations of these press releases):
| http://www.irsn.fr/FR/Actualites_pr...Seisme-Japon_Point-situation-20032011-06h.pdf