Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[Borek]

I simply said that I wanted to estimate its mass if we were able to calculate the energy involved during the explosion as I know the height at which these items have gone up.

No matter how many times you will repeat it, the answer will be still the same - you are trying to do thing that is impossible.

I suggest you open a new thread in the General Physics subforum, as this discussion is OT here.

 

[|Fred]

You can not trust any of the readings/reports. Because it's TEPCO and the press most of the time do not know what they are writing about

I won't go as far as giving 100% trust to tepco's number has they have been proven wrong, but I would not comment on TV press report that more often than not, are misleading.

 

[artax]

Hello, I've been lurking here for the last month. I was happy to find a place where people actually knew what they were talking about. For that, thank you.

I found a Tepco press site with images and videos, some that I have not yet seen on any other sites.
http://www.tepco.co.jp/en/news/110311/

I found the "Sampling in Spent Fuel Pool of Unit 4" video very interesting. I was surprised it is in such good shape, at least to my "not-a-scientist" eyes.
http://www.tepco.co.jp/en/news/110311/images/110414_1f_1.zip

If you have already seen these, I apologize and I will go back to my lurking.

Excellent link thanks!

 

[TCups]

Nice one!

not read the last 20 pages but there's a good situation update here:-

http://cryptome.org/0003/daiichi-assess.pdf

I know there are translation problems, but I just love the way they say "unit one is relatively stable"!

Relatively! ... to what!

The status report is dated 26Mar. Is there a more recent version of this document?

 

[Krikkosnack]

http://nige.wordpress.com/2011/03/1...-fukushima-dai-ichi-nuclear-reactor-number-1/

the overpressure-impulse from an air burst 1 kiloton or 1,000 tons of TNT equivalent nuclear explosion is only 10 kPa-sec or 1.4 psi-seconds at 100 metres and varies inversely with distance, 200 psi-seconds or 1.4 MPa-seconds of overpressure impulse (which Dr Conrad V. Chester of Oak Ridge National Laboratory calculates is needed to rupture the steel pressure vessel containing a nuclear reactor core) requires the distance between the steel reactor vessel and the 1,000 tons of TNT explosion to be just 0.7 metre (70 cm). This blast overpressure impulse can’t arise from a hydrogen gas explosion; there simply isn’t enough energy available!

 

[artax]

How thick is the containment vessel? And what's the temperature difference across it (inside to outside)? I'd guess that the thickness of the steel doesn't matter much relative to the (probably low) heat transfer coefficients at the inner & outer surfaces.

Early on I heard a value of six inches, or 150mm, but I later heard 100mm thick, however the thermal conductivity of steel would mean temperature of insid and out would be the same unless there was a very rapid temp change and you took measurements within a few tens of seconds.

 

[artax]

The status report is dated 26Mar. Is there a more recent version of this document?

They're undoubtedly doing a lot of work vetting/editing/sensoring any info or data before releasing to general public. this is what is so annoying... and why we're all on here.

 

[artax]

I'll start a new attempt to raise awareness for an annotated picture posted before:

The annotation characterizes the curved deformation as damage from heat. Isn't that plausible? Do we have any reliable information on the sequence of events in No4 (fire before/after explosion)

@TCups, you posted the picture, You remember where you got it?

Hey Tcups, I was discussing this with my Dad a while back and he immediately suggested that the roof bowed upwards in the explosion bending the girders and pulling the walls in at the top.

PS sorry for all these posts, just been away and not read anything for days! (only have t'internet at work)

 

[TCups]

Hey Tcups, I was discussing this with my Dad a while back and he immediately suggested that the roof bowed upwards in the explosion bending the girders and pulling the walls in at the top.

PS sorry for all these posts, just been away and not read anything for days! (only have t'internet at work)

Hmmm . . .

The northeast corner of Bldg 4 is odd, for sure. I don't believe it was the whole roof that lifted -- maybe the northeast corner might have had that effect. But if so, why?! What happened in the northeast corner of that building.

@liamdavis:

Maybe you could lend your expertise here, sir. Also, can you comment on your assessment of the possibility that the concussion and shock wave from the Bldg 3 explosion might have done structural damage to the northeast corner of Bldg 4 that wasn't readily visible from the outside. Perhaps after the blast at Bldg 3, the northeast corner of Bldg 4 was simply the weakest link.

 

[PietKuip]

Early on I heard a value of six inches, or 150mm, but I later heard 100mm thick, however the thermal conductivity of steel would mean temperature of insid and out would be the same unless there was a very rapid temp change and you took measurements within a few tens of seconds.

The thermal resistance of such a length of steel is quite high, you can keep one end of a steel rod in your hand while the other end is hot. Also, the content of the RPV has a large heat capacity. Flooding the outside with cooling water is not an effective way of removing the heat generated inside. I am too lazy right now the look up the numbers (what thermal power is supposed to be generated a month after scramming, the surface area of the RPV, the thermal conductivity), but my gut feeling is that the equilibrium temperature inside would come out too high if this were the only method of cooling.

Maybe the want to flood the drywell because there are holes in connections that are at or below the level of the fuel rods? Holes that prevent increasing the water level?

 

[etudiant]

Has anyone had the time to take an informed look at the TEPCO road map?
It reads as a logical wish sequence, but the specifics of how anything gets done are scant.
Looking at the rubble strewn site it is difficult to reconcile the three months expectation for a clean up phase with the means thus far deployed.
Three decades might be more correct at the current rate of progress.

 

[Rive]

It is hard to escape the conclusion that water flashing to steam occurred at Bldg 3 and that the source of the explosion in Bldg 4 had to ultimately be the spent and un-spent fuel in the SFP.

Hi,

Just two points to consider:

- by the look of the third floor (from top) it's interesting that the panels were blown off right and left around the SFP - but not where the SFP is. Was it the SFP itself what protected those panels from the blastwave, or just there was not enough place between the SFP and the wall to generate enough blast power?

- there is a door (I don't know where it leads) on the FHM of U4 - the door is barely bent, but the wall and pillars opposite the door are completely gone. How is such a thing possible?

 

[rowmag]

Maybe the want to flood the drywell because there are holes in connections that are at or below the level of the fuel rods? Holes that prevent increasing the water level?

That was the reason offered on the news tonight (NHK), for what it's worth.

 

[elektrownik]

How this is possible ? Unit 4 core location is 5C more than SFP, how empty core can be so hot ?
This can't be water from SFP becouse it temperature is bigger than this in SFP.
This shouldn't be exploded fuel from SFP becouse tepco tell us that fuel is not much damaged.
[PLAIN]http://img191.imageshack.us/img191/6088/sssssssd.jpg

 

[rowmag]

As for Unit 4, the shattered upper mast of the FHM seems to indicate a violent event in the SFP with lots of energy transferred to the mast, but perhaps not so much damage to the remainder of the FHM.

I'm not convinced the mast is broken. Several views from around the 3:00 mark onwards in the following video suggest, to me at least, that the upper part of the mast ends naturally there. The end looks too flat and clean to be a break:

 

[TCups]

I'm not convinced the mast is broken. Several views from around the 3:00 mark onwards in the following video suggest, to me at least, that the upper part of the mast ends naturally there. The end looks too flat and clean to be a break:

Yes, I think you may be right. At first glance, I had misinterpreted a superimposed wire as a crack. So it was not blasted away and cracked, but in any case, it appears that the lower end of the mast is missing.

 

[gmax137]

Early on I heard a value of six inches, or 150mm, but I later heard 100mm thick, however the thermal conductivity of steel would mean temperature of insid and out would be the same unless there was a very rapid temp change and you took measurements within a few tens of seconds.

The thermal resistance of such a length of steel is quite high, you can keep one end of a steel rod in your hand while the other end is hot. Also, the content of the RPV has a large heat capacity. Flooding the outside with cooling water is not an effective way of removing the heat generated inside. I am too lazy right now the look up the numbers (what thermal power is supposed to be generated a month after scramming, the surface area of the RPV, the thermal conductivity), but my gut feeling is that the equilibrium temperature inside would come out too high if this were the only method of cooling.

Maybe the want to flood the drywell because there are holes in connections that are at or below the level of the fuel rods? Holes that prevent increasing the water level?

Sorry, I was mixing up what you originally had in mind - I was thinking they were flooding the exterior of the containment vessel (probably 1/2 to 3/4 inch steel); seems you are saying they are flooding the containment, in that case the thickness of the reactor vessel (probably 4 to 8 inch steel) is pertinent. External cooling of the vessel is not an unknown idea for severe accidents with core damage.

On the other hand, you may be correct about leak paths preventing vessel filling. Someone has mentioned the recirc pump seals as potential leak paths. Again, I apologize for confusing your post.

 

[rowmag]

Apparantly NISA announced that the reactor builing No 4 is now flooded in 5 meters of water. Anyone to explain this? Do they mean the SFP?

It is not the SFP, it is in the basement. Source unknown, possibly left over from the tsunami, according to the news tonight (Houdou Station).

 

[TCups]

How this is possible ? Unit 4 core location is 5C more than SFP, how empty core can be so hot ?
This can't be water from SFP becouse it temperature is bigger than this in SFP.
This shouldn't be exploded fuel from SFP becouse tepco tell us that fuel is not much damaged.
[PLAIN]http://img191.imageshack.us/img191/6088/sssssssd.jpg[/QUOTE]

https://www.physicsforums.com/attachment.php?attachmentid=34539&d=1303130979

Well, the SFP and the empty reactor vessel are connected by the fuel transfer chute. It also seems logical that the gate to the equipment pool would be open, too.

The thermal signal from SFP4 is partially obscured by the FHM, the overhead crane and debris on the roof. The open reactor vessel is partially obscured by the roof girders. The equipment pool is partially obscured by a portion of the damaged roof.

The question might be "How hot is the SFP under the FHM?" I think perhaps we see only the southwest corner of the SFP. How likely is it that the small portion of the SFP seen in the southwest corner would be the hottest spot in the pool? Still, the temperature in the reactor vessel seems relatively warm.

 

[TCups]

Hi,

Just two points to consider:

- by the look of the third floor (from top) it's interesting that the panels were blown off right and left around the SFP - but not where the SFP is. Was it the SFP itself what protected those panels from the blastwave, or just there was not enough place between the SFP and the wall to generate enough blast power?

- there is a door (I don't know where it leads) on the FHM of U4 - the door is barely bent, but the wall and pillars opposite the door are completely gone. How is such a thing possible?

Rive: Can you please link to the images you reference? Thanks.

 

[default.user]

Sorry, my english is verry bad. I use my german. maybe the translater works fine. ;=))

1. Hatten die Explosionen genug Kraft, um das Wasser aus den Abklingbecken zu ziehen?

2. Wie lange standen die Abklingbecken nach den Explosionen trocken?

Danke

 

[TCups]

Sorry, my english is verry bad. I use my german. maybe the translater works fine. ;=))

1. Hatten die Explosionen genug Kraft, um das Wasser aus den Abklingbecken zu ziehen?

2. Wie lange standen die Abklingbecken nach den Explosionen trocken?

Danke

1. The explosions had enough force to pull the water from the cooling pond (spent fuel pool)?

At Building 3, yes. It is probable that the explosion was steam, and the steam was the vaporized water leaving the cooling pool.

At Building 4, it is not known with certainty, but it is possible and perhaps probable. The spent and un-spent fuel in the pool would have to be partially uncovered to become damaged and to then produce the hydrogen gas. It was hydrogen gas that most likely caused the explosion in Building 4.

2. As long as (For how long were) the cooling ponds were dry after the explosions?

I do not know, but perhaps someone can give a better answer. Attempts were made soon after the explosions at Building 3 and 4 to add water by helicopter drops and by spraying with fire hoses, but I do not know how long it actually took to again cover the fuel in the spent fuel pools.

 

[Astronuc]

1. The explosions were over the SFP / Die Explosionen waren über (oben) den Abklingbecken

The explosions were of short duration / Die Explosionen dauern nicht so lang (sie hatten kurze Zeitdauern).

2. That is not clear / Das ist nicht klar (oder daß ist unbekannt).

 

[default.user]

Danke sehr.

Thank you for the answers.

 

[Rive]

Rive: Can you please link to the images you reference? Thanks.

Sorry.
The first attachment below about the U4: the two wall sections closest to the SFP (distance could be about one meter or so between the wall and the SFP) are OK, the next to them to left gone. On the other wall every sections are gone, but the first three, which has the pool and the containment just a few meters back are with less damage than the rest as I see. I don't know the source of the picture.

The second attachment about the knocked door is from the sample-taking process video.

 

[Rive]

Ooops. TCups, I think I've found a picture about that mysterious 'Fuel Prep. Machine'.

It's from here: http://www.nucleartourist.com/areas/bwr-in1.htm
"Inspecting a BWR fuel assembly"
http://www.nucleartourist.com/images/Finsp1.gif

 

[TCups]

Sorry.
The first attachment below about the U4: the two wall sections closest to the SFP (distance could be about one meter or so between the wall and the SFP) are OK, the next to them to left gone. On the other wall every sections are gone, but the first three, which has the pool and the containment just a few meters back are with less damage than the rest as I see. I don't know the source of the picture.

The second attachment about the knocked door is from the sample-taking process video.

See MiceAndMen's post #4045, with this diagram linked:
http://i.min.us/ikukv6.jpg

Looks more like about 3 meters separation on the south side if the diagram is representative of the construction at Fukushima.

 

[Rive]

See MiceAndMen's post #4045, with this diagram linked:
http://i.min.us/ikukv6.jpg

Looks more like about 3 meters separation on the south side if the diagram is representative of the construction at Fukushima.

I think the other link of that post is more useful in this case: that space to the south wall mostly full (or, at least, closed from both side) with the SFP-machinery (skimmer tanks and so). But I can be wrong with the distances.

 

[mikefj40]

TEPCO's roadmap suggests that the SFP in #4 needs support from underneath. That remedy is Action No.26, to be done in the next three months.

http://ex-skf.blogspot.com/2011/04/fukushima-i-nuke-plant-reactor-4-spent_17.html

 

[Astronuc]

April 18 update from TEPCO

http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/f12np-gaiyou_e.pdf

Event summary
Estimated activity release
Seismic data
Plans to move forward

TEPCO summary of roadmap
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110417e12.pdf
from - http://www.tepco.co.jp/en/press/corp-com/release/11041707-e.html

Roadmap for Fukushima Daiichi restoration
18 April 2011
http://www.world-nuclear-news.org/RS-Roadmap_for_Fukushima_Daiichi_restoration-1804114.html

 

[Nullpunkt]

Hmmm . . .

The northeast corner of Bldg 4 is odd, for sure. I don't believe it was the whole roof that lifted -- maybe the northeast corner might have had that effect. But if so, why?! What happened in the northeast corner of that building.

@liamdavis:

Maybe you could lend your expertise here, sir. Also, can you comment on your assessment of the possibility that the concussion and shock wave from the Bldg 3 explosion might have done structural damage to the northeast corner of Bldg 4 that wasn't readily visible from the outside. Perhaps after the blast at Bldg 3, the northeast corner of Bldg 4 was simply the weakest link.

From the picture you attached I think nothing from inside the building has damaged the roof. Something has landed on top of the roof. It hit not directly from overhead, more a bit from the side, so it bend over the wall.
If you take a closer look to the object it is partly above the roof skeleton and the main part stamped into the building construction.

Where did you find this picture? I could not find any other images of this part of the building.

 

[TCups]

From the picture you attached I think nothing from inside the building has damaged the roof. Something has landed on top of the roof. It hit not directly from overhead, more a bit from the side, so it bend over the wall.
If you take a closer look to the object it is partly above the roof skeleton and the main part stamped into the building construction.

Where did you find this picture? I could not find any other images of this part of the building.

Here:

http://cryptome.org/eyeball/daiichi-npp/daiichi-photos.htm

 

[Jorge Stolfi]

How this is possible ? Unit 4 core location is 5C more than SFP, how empty core can be so hot ?[/PLAIN]

Unit #4's SFP is almost completely covered by the fuel handling machine that crashed into it. Then there are roof beams etc. above it. So it is possible that the infrared image is seeing the water in the reactor, but not that in the SFP.

 

[elektrownik]

And my new image of #4:
[PLAIN]http://img535.imageshack.us/img535/3165/gggss.png

 

[Jorge Stolfi]

IN the last three NISA releases (98, 99, 100) they started giving two CAMS readings for the drywell (A,B) and two for the suppression torus (A,B), instead of one.

For units #2 and #3, the previous single readings match closely the new (A) readings. Fine.

For unit #1, however, neither (A) nor (B) match the previous single readings. However, the previous readings would match the new (A) readings multiplied by 10. Specifically, the readings given as 1.07×10⁰, 1.00×10⁰ and 9.92×10^-1 Sv/h should be multiplied by 10.

The CAMS readings are given in exponential notation. My guess is that TEPCO made a mistake in the exponent of the S/C readings for unit #1, either in the last three releases or in all the previosu ones. I caught a couple of such mistakes before, so that is not out of the question. Moreover, it is almost certain that they produce each fax sheet by editing the previous one. (There is a spurious hyphen in front of a temperature reading that looks like a minus sign; it has been there forever.)

I will keep TEPCO's values in my next plot, until the issue is clarified.

 

[TCups]

Unit #4's SFP is almost completely covered by the fuel handling machine that crashed into it. Then there are roof beams etc. above it. So it is possible that the infrared image is seeing the water in the reactor, but not that in the SFP.

The verbiage "crashed into" may be a bit strong, given the current video of SFP 4 and the almost intact FHM

 

[cphoenix]

1. The explosions had enough force to pull the water from the cooling pond (spent fuel pool)?

At Building 3, yes. It is probable that the explosion was steam, and the steam was the vaporized water leaving the cooling pool.

Building 3 seems to have soot on it.

Also, wasn't there a fireball in the building 3 explosion video?

When you talk of vaporized water leaving the cooling pool, that sounds like my theory of low pressure high volume steam explosion. But I thought that fit building 4 a lot better than building 3.

At Building 4, it is not known with certainty, but it is possible and perhaps probable. The spent and un-spent fuel in the pool would have to be partially uncovered to become damaged and to then produce the hydrogen gas. It was hydrogen gas that most likely caused the explosion in Building 4.

Why do you say there was hydrogen gas in building 4? There was damage below-decks in building 4, where hydrogen would not have gone. Also, a hydrogen explosion would probably have done a lot more symmetrical damage to the building, knocking off all the top row of panels.

Chris

 

[Jorge Stolfi]

The verbiage "crashed into" may be a bit strong, given the current video of SFP 4 and the almost intact FHM

But my impression is that the FHM is much lower than it should be, and part of it is below the main (top) floor, i.e. inside the pool. Is that right?

 

[TCups]

From the picture you attached I think nothing from inside the building has damaged the roof. Something has landed on top of the roof. It hit not directly from overhead, more a bit from the side, so it bend over the wall.
If you take a closer look to the object it is partly above the roof skeleton and the main part stamped into the building construction.

Where did you find this picture? I could not find any other images of this part of the building.

Well whaddya know . . .
Nullpunkt may be right. The damage to the northeast corner of Bldg 4 does look like an impact from something that fell on it. That would explain the north wall collapsing inward, except . . . what fell on it? If it is something from the explosion at Bldg 3, it must have had one long "hang time", or there was another explosion we missed. I guess you don't look for something if you don't think it could have happened.

@|Fred

Your the skeptic, Fred. What do you think? Does a falling object pass the "|Fred Test"?

 

[TCups]

But my impression is that the FHM is much lower than it should be, and part of it is below the main (top) floor, i.e. inside the pool. Is that right?

I am not sure that is right, but I don't know. Heck, I am not sure now that I "know"anything about any of these events.

 

[TCups]

Building 3 seems to have soot on it.

Also, wasn't there a fireball in the building 3 explosion video?

When you talk of vaporized water leaving the cooling pool, that sounds like my theory of low pressure high volume steam explosion. But I thought that fit building 4 a lot better than building 3.



Why do you say there was hydrogen gas in building 4? There was damage below-decks in building 4, where hydrogen would not have gone. Also, a hydrogen explosion would probably have done a lot more symmetrical damage to the building, knocking off all the top row of panels.

Chris

I retract my earlier statement, sir. I cannot say with any reasonable degree of certainty that I know what specifically caused any of the explosions except perhaps for Building 1, and only that because it occurred in immediate temporal proximity to venting of hydrogen gas from the containment.

 

[|Fred]

But my impression is that the FHM is much lower than it should be, and part of it is below the main (top) floor, i.e. inside the pool. Is that right?

Personal estimate is about 2m bellow where it should be, It derailed into really

 

[TCups]

Personal estimate is about 2m bellow where it should be, It derailed into really

OK, but I meant what do you think about something having fallen into the northeast corner of the roof of Building 4?

 

[etudiant]

Is there any logical explanation for TEPCOs concern about the structural stability of the reactor 4 SFP?
A hydrogen explosion in the SPF would have left the support structure unscathed and there was no fuel lower down to do damage.
So that leaves only the reactor 3 explosion as a suspect. One part of that explosion did seem very horizontal and looked to impinge on the reactor 4 building.
There has not been any good explanation of this, which preceded the roof blowing off.
Can anyone provide insight?

 

[Jorge Stolfi]

I have updated my plots of the #1--#3 reactor variables to TEPCO-NISA release 100 (dated 2011-04-18 15:00).

http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/plots/cur/Main.html"

I had to change the format of my files to accommodate the new readings that have been provided in the recent releases (and the 3-digit NISA release numbers! Perhaps I should plan already for 4 digits...) The new data include the drywell and torus temperatures, and the alternative "B" readings for drywell and torus CAMS. I have also provided space for the alternative ("A" or "B") readings of water level and core pressure; these have been available for some time, but I had entered only one of them until now. Over the next few days I hope to add the past readings of these alternate measurements.

Beware that the CAMS readings for unit #1 suppression chamber may be wrong by a factr of 10, as noted in my previous post.

 

[NUCENG]

I've been looking for the photo evidence of a second explosion at unit 3 and haven't found anything conclusive, yet. But I have some other information that tends to bring more doubt of a big hydrogen explosion in the Unit 4 SFP.

Some here have expressed a lot of doubt about TEPCO's information. Since I am using their data, not everyone will agree.

They have described damage to fuel in the Unit 4 SFP as minor. Their samples indicated concentrations of I-131 at 220 Bq/cm^3 and Cs-137 at 93 Bq/cm^3. I took the conservative assumprion that the core just offloaded was the only contributor yo that radioactivity. assumed only a release of 5% for gap release. In a volume of the size of the SFP absent any dilution, but accounting for 30 days of decay would produce activities for CS and I in the range of 1E6 Bq/cm^3. You would have to feed and bleed for a full turnover of SFP volume 16 or 17 times to reach the measured concentrations. If their sample is correct, fuel damage was minor as they claim.

 

[TCups]

I've been looking for the photo evidence of a second explosion at unit 3 and haven't found anything conclusive, yet. But I have some other information that tends to bring more doubt of a big hydrogen explosion in the Unit 4 SFP.

Some here have expressed a lot of doubt about TEPCO's information. Since I am using their data, not everyone will agree.

They have described damage to fuel in the Unit 4 SFP as minor. Their samples indicated concentrations of I-131 at 220 Bq/cm^3 and Cs-137 at 93 Bq/cm^3. I took the conservative assumprion that the core just offloaded was the only contributor yo that radioactivity. assumed only a release of 5% for gap release. In a volume of the size of the SFP absent any dilution, but accounting for 30 days of decay would produce activities for CS and I in the range of 1E6 Bq/cm^3. You would have to feed and bleed for a full turnover of SFP volume 16 or 17 times to reach the measured concentrations. If their sample is correct, fuel damage was minor as they claim.

Yes, but doesn't TEPCO also report the damage at Bldg 4 as a "hydrogen explosion"?

 

[MadderDoc]

Well whaddya know . . .
Nullpunkt may be right. The damage to the northeast corner of Bldg 4 does look like an impact from something that fell on it. That would explain the north wall collapsing inward, except . . . what fell on it? <..>

Isn't the simple answer: Parts of the roof.

There must have been an explosion inside the building, including in the upper floor, everyone would agree. Both the walls, and the roof must have been affected by that explosion. The wall pillars and panels must have been pushed outward by it, the roof however must have been blown upwards.

So, in the moment after the explosion we have had a weakened pillar and wallpanels structure still standing below, and -- 100s of tons of roof in the air some distance above it.

What goes up must come down, so the roof did, and some of it incidentally on top of the north wall. And since the wall had already been buckled outward by the explosion, the next powerful hit from above could leave it only even more collapsed, and even further pushed outward.

 

[NUCENG]

Yes, but doesn't TEPCO also report the damage at Bldg 4 as a "hydrogen explosion"?

Yes, in their initial reports they called it hydrogen.


Here was their first release:

Press Release (Mar 15,2011)
Damage to the Unit 4 Nuclear Reactor Building at Fukushima Dai-ichi Nuclear Power Station


At approximately 6:00am, a loud explosion was heard from within the
power station. Afterwards, it was confirmed that the 4th floor rooftop
area of the Unit 4 Nuclear Reactor Building had sustained damage.

World Nuclear News :

17MARCH
The explosion at unit 4 is thought to have been from a build-up of hydrogen in the area near the used nuclear fuel pond. It severely damaged the building, as well as that of adjacent unit 3, with which it shares a central control room.

So they were saying that there was some simultaneous damage to both Unit 3 and Unit 4.

But now the damage to fuel in the SFP on Unit 4 does not seem to support that scenario.

It keeps bringing me back to a second explosion in Unit 3.

I can't prove it, but I haven't seen anything that fits better.

 

[elektrownik]

What about this strange idea ?
[PLAIN]http://img864.imageshack.us/img864/770/7d39a2e665024e3f8856f31.jpg