Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[unlurk]

Ever seen a volcano erupt?

Possibly I'm being misunderstood.

I am not saying there was a nuclear explosion in the sfp.

On the basis of all the known information, I believe there was a criticality which occurred in the fuel pond.

The heat generated by the criticality created the steam explosion visible in the videos of the explosion of number 3.

The (sideways) hydrogen explosion was a powerful blast, but it was a mere puff when compared to the steam explosion which followed.

Please note that the vertical column of "steam" seen in the #3 blast was brown because it contained debris from the hydrogen blast and contents of the sfp.

This theory also appears to be supported by the presence of very "hot" radioactive debris around the site and the detection of neutron activity outside the site boundary.

Units 3 and 4 are the only suspects as the source of all the radiation around the site as far as I know.

And #4 may not have contributed much to the foul environment around the plant.

 

[Jorge Stolfi]

the column of "steam" reached a height of 500 meters or so very quickly in a strong SE breeze. I have seen a lot of steam releases in my time, but never one with that much energy.

Could that much steam be generated from H2 + O2 ? The interior space of floors 3-4-5 is somewhat less than 30,000 m^3. Wikipedia says that explosion can happen with H2 concentration from 4% to 74%. If we take 40% (max that will burn anyway), that would be at most 12,000 m^3 of H2, which after the explosion would would become 12,000 m^3 of hot steam, which at atmospheric pressure would expand adiabatically to ... huh ... (end of my physics).

Anyway, 12,000 m^3 of H2 at 1 bar ~ 1000 kg of H2 <--> 9000 kg of H2O So the maximum H2 explosion assumed above would generate a mushroom comparable to that of the explosion of a boiler with 9 m^3 of liquid water, overheated to some temperature TBD. Is that compatible with your experience?

However for this maximum scenario we need 9 tons of water combining with zirconium (in the core, in the SFP, or both) to produce that 1 ton of H2. Is this reasonable?

If we take the lower figures, we get perhaps 20,000 m^3 of space filled with 4% H2. That means less than 70 kg of H2 <--> 630 liters of liquid water. That seems more reasonable as far as H2 generation goes; but would it yield enough steam for the mushroom we saw?

If we cannot match the amount of H2 likely to have been produced with the size of the mushroom cloud, two other possibilities are an explosive rupture of the RPV (several tons of superheated water there), or a criticality in the SFP (vaporizing some of the water).

 

[TCups]

Possibly I'm being misunderstood.

I am not saying there was a nuclear explosion in the sfp.

On the basis of all the known information, I believe there was a criticality which occurred in the fuel pond.

The heat generated by the criticality created the steam explosion visible in the videos of the explosion of number 3.

The (sideways) hydrogen explosion was a powerful blast, but it was a mere puff when compared to the steam explosion which followed.

Please note that the vertical column of "steam" seen in the #3 blast was brown because it contained debris from the hydrogen blast and contents of the sfp.

This theory also appears to be supported by the presence of very "hot" radioactive debris around the site and the detection of neutron activity outside the site boundary.

Units 3 and 4 are the only suspects as the source of all the radiation around the site as far as I know.

And #4 may not have contributed much to the foul environment around the plant.

@Unlurk:
Understand. Ultimately, it can be debated as to the precise source of heat that drove the steam explosion -- sudden criticality or otherwise, but not that a steam explosion occurred, IMO. The fundamental difference between the explosion at Unit 3 and the others was the component of the steam explosion, whatever its exact precipitating cause.

Basically, the water in the SFP would have been heated to the boiling point without a sudden criticality. And a hydrogen explosion would have added additional heat and, perhaps more importantly, sudden agitation of the heated water. It is plausible that a steam explosion may have occurred without or with sudden criticality. Based on the evidence and opinions of others here on the PF (Astronuc principal among them) I don't think sudden criticality occurred in SFP3.

BTW, I was pleased to see yet another new member also become a contributor to the PF. I did so, too, and believe the value received was well worth the contribution. Others are also encouraged to consider becoming contributing members. Thanks.

 

[robinson]

The explosion of Building 3 is fascinating. I would bet if there was video of the Building 4 explosion, it would be far more interesting as well.

 

[jlduh]

As general information about currently discussed safety policies evolutions in case of nuke accidents, i post this translation of a french article from 5th of May. Today have been hold auditions at the french parliament to discuss how to adress in the future, and after Fukushima, "unthinkable scenarios of accidents". "Thinking the unthinkable" is the main goal of a kind of task force that has been put in place after Fukushima where a succession of events ended up in a scenario that was never foreseen by plant designers nor self defense forces who had to cope with the desaster. They ARE NOW CLEARLY RECOGNIZING THAT CRISIS AND RISKS SCENARIOS ARE OFTEN TOO SIMPLISTIC AND DO NOT INCLUDE POSSIBLE DOMINOS EFFECTS (I mentioned this recently concerning the NRC SFP risk reassessment study, which never adressed the possibility that the reactor below the SFP could explode or trigger an explosion devastating the pools placed on the "attic"!).

Note they are also seriously considering the need to develop ressources able within 48 hours to be sent on site (with helicopters) with all the means necessary to provide an effective mobile backup of power AND water to deal with a total blackout situation in a NPP for all the reactors (loss of cold source and loss of power, from primary AND from onsite backup).

http://translate.google.fr/translat...urete-nucleaire-imaginer-l-inimaginable,23027

 

[robinson]

With out a back up cooling system nothing seems to be able to prevent a meltdown when something damages the heat exchange. Be it cooling towers, or intake/outflow from a river/ocean, if the cooling system fails, for what ever reason, there will be big trouble.

How to fix that?

 

[mscharisma]

This livecam is some 13 km away from fukushima, very strong telephoto lens is used and these do tend to showhttp://en.wikipedia.org/wiki/Distortion_(optics)" . You have just re-discovered the pin-cushion phenomena. Once you factor away the distortion of the lens then you can make a judgement on the verticality of the building,

Even in the live web cam, the left side towers are perfectly straight, whereas the building towards the right are leaning to the right. Hope this doesn't win the "dumbest question of the day" prize, but wouldn't the distortion go from the center (not distorted) of the picture towards both sides equally?

 

[AntonL]

Even in the live web cam, the left side towers are perfectly straight, whereas the building towards the right are leaning to the right. Hope this doesn't win the "dumbest question of the day" prize, but wouldn't the distortion go from the center (not distorted) of the picture towards both sides equally?

correct, unless electronic zoom or electronic selection of a part of the complete frame is transmitted

EDIT: correction, I took another frame of the TBS/JNN feed and drew some lines
looks OK to me
[PLAIN]http://k.min.us/inqMBW.JPG

 

[Dmytry]

As general information about currently discussed safety policies evolutions in case of nuke accidents, i post this translation of a french article from 5th of May. Today have been hold auditions at the french parliament to discuss how to adress in the future, and after Fukushima, "unthinkable scenarios of accidents". "Thinking the unthinkable" is the main goal of a kind of task force that has been put in place after Fukushima where a succession of events ended up in a scenario that was never foreseen by plant designers nor self defense forces who had to cope with the desaster. They ARE NOW CLEARLY RECOGNIZING THAT CRISIS AND RISKS SCENARIOS ARE OFTEN TOO SIMPLISTIC AND DO NOT INCLUDE POSSIBLE DOMINOS EFFECTS (I mentioned this recently concerning the NRC SFP risk reassessment study, which never adressed the possibility that the reactor below the SFP could explode or trigger an explosion devastating the pools placed on the "attic"!).

Note they are also seriously considering the need to develop ressources able within 48 hours to be sent on site (with helicopters) with all the means necessary to provide an effective mobile backup of power AND water to deal with a total blackout situation in a NPP for all the reactors (loss of cold source and loss of power, from primary AND from onsite backup).

http://translate.google.fr/translat...urete-nucleaire-imaginer-l-inimaginable,23027

Great to see sane approach. Just what I wanted to see. Complete with helicopter delivery. I wonder if they will also add helipads to the roofs (those that can withstand weight) . Thinking the unthinkable approach should include backup landing zones, as in the event of flooding there may be a problem, and it needs to be known in advance which roofs can and can't be landed onto, and where. Such things IMO are a proxy whenever there's any new thinking or it is same old doing just the absolute bare minimum.

 

[yakiniku]

Long time lurker here. I enjoy the open discourse. I haven't really had anything to contribute until now. My partner who is Japanese brought this blog post to my attention. It is from Taro Kono, who is in the house of representatives (LDP, opposition to current government):

http://www.taro.org/2011/05/post-996.php

In particular this section:

"エネ庁の若手官僚から添付ファイルが３通ついたメールが来た。

その一
５月１日の政府・東電統合本部全体会合の議事録。
『このままいくと８日にも高濃度の放出が行われる。』
『細野補佐官から，本件は熱交換機の設置といった次のステップに進む上で非常に重要である，また，（今後，放射性物質が外に排出され得るという点で，）汚染水排出の際の失敗を繰り返さないよう，関係者は情報共有を密に行い，高い感度を持って取り組んで欲しい，とする発言があった。』"

Translation (non-literal and our understanding):

I received 3 emails with attachments from junior government officials in the energy department.

The first email:
Minutes of meeting between TEPCO and the government on the 1st May.
"If the current situation continues, high density radiation will be released on the 8th May."
"Mr Hosono said: It is very important to go to the next step regarding the installation of the heat exchanger machine. For the concerned parties, be careful of the sharing of information with high sensitivity so that the same mistakes aren't made again like the release of the radiated water previously.

The second and third emails aren't related so we didn't translate it. It isn't clear from the text the way the radiation will be released. ie airborne or via water.

The aforementioned energy department English homepage is this:
http://www.enecho.meti.go.jp/english/index.htm

Perhaps those who are following the work and/or parameters of the reactors could hypothesise what they are thinking about doing.

 

[etudiant]

Long time lurker here. I enjoy the open discourse. I haven't really had anything to contribute until now. My partner who is Japanese brought this blog post to my attention. It is from Taro Kono, who is in the house of representatives (LDP, opposition to current government):

http://www.taro.org/2011/05/post-996.php

In particular this section:

"エネ庁の若手官僚から添付ファイルが３通ついたメールが来た。

その一
５月１日の政府・東電統合本部全体会合の議事録。
『このままいくと８日にも高濃度の放出が行われる。』
『細野補佐官から，本件は熱交換機の設置といった次のステップに進む上で非常に重要である，また，（今後，放射性物質が外に排出され得るという点で，）汚染水排出の際の失敗を繰り返さないよう，関係者は情報共有を密に行い，高い感度を持って取り組んで欲しい，とする発言があった。』"

Translation (non-literal and our understanding):

I received 3 emails with attachments from junior government officials in the energy department.

The first email:
Minutes of meeting between TEPCO and the government on the 1st May.
"If the current situation continues, high density radiation will be released on the 8th May."
"Mr Hosono said: It is very important to go to the next step regarding the installation of the heat exchanger machine. For the concerned parties, be careful of the sharing of information with high sensitivity so that the same mistakes aren't made again like the release of the radiated water previously.

The second and third emails aren't related so we didn't translate it. It isn't clear from the text the way the radiation will be released. ie airborne or via water.

The aforementioned energy department English homepage is this:
http://www.enecho.meti.go.jp/english/index.htm

Perhaps those who are following the work and/or parameters of the reactors could hypothesise what they are thinking about doing.

Perhaps this is related to the temperature rise discussed earlier in reactor 3.
TEPCO on Wednesday has increased the flow of water to that reactor to 9 tons/hr from 7 tons/hr.
Clearly the situation remains far from stable.
With the water in the plant and the reactor temperatures both rising, maybe there should be a reappraisal of the strategy.

 

[razzz]

Only Unit 1 is capable of holding any pressure. Unit 2 & 3 are at ambient air. How they expect to do a closed loop heat exchange recirculating contaminated water in Unit 1 is beyond me. Sounds desperate. Maybe they will figure that out if they can get close enough to look at the plumbing.

If the readings are to be believed, guys here keeping track of the pressures should be able to predict a likely overpressure suspect.

Unit 3 had a well formed mushroom cloud which takes a lot of heat to accomplish, while both events are happening i.e. hydrogen explosion with water flashing to steam, something else is also going on. Units 1 & 4 frameworks performed as intended with typical pent up hydrogen explosions. Unit 1 was venting radioactive wastes amongst the hydrogen release emanating from core as was Unit 3's venting.

Rust looking areas on steel was aided with saltwater dumping and pumping and part of the roofing material is likely galvanized corrugated steel plates and not aluminum.

 

[jim hardy]

Triumph

i was sloppy in my wording a few pages back regarding yellow object in video.

I said "right next to", i should have said "adjacent to left " and if that's where you looked you have the right object. It's the video recorded from inside a vehicle, they drive up by the reactor building and stop to film a red fire truck spraying water. i lost the link, sorry... but sounds like you found it.

old jim

 

[yakiniku]

"If the current situation continues, high density radiation will be released on the 8th May."

In reply to myself and clarification regarding the translation, this sentence implies that the radiation will be released intentionally and not unintentionally (due to a consequence of some event that might happen) on the 8th May.

 

[jim hardy]

I agree with you guys, something was different about unit 3. Way more energetic.

I too have looked for a mechanism to cause criticality in the pool but can't find one. It'd take something to remove the poison to let it go critical. and they weren't spraying the pools yet i believe.
I even looked into fission cross sections for fast neutrons on premise boron is transparent to them and maybe removing moderator by uncovering half the fuel made it into a fast reactor,
but decided that to best of my meager understanding the cross sections are a decade too low even at 3n per fission Pu ~5%.

Maybe one of you heavy duty reactor physics guys can confirm? Just an "Are you crazy?" would suffice. I'm asking because i don't know for sure, not to make points.

i had one course in it and that was over forty years ago and i struggled then. my field was PWR instruments not BWR nucleonics.
but it'd be intuitive to somebody who does it every day.

so i am watching you folks brainstorm.

will be quiet now. old jim

 

[michael200]

H2 detonation at u3 caused the fuel pool to go critical?? About as likely as caused by aliens with death rays. Why are people giving credence to this nonsense.

 

[TCups]

FORCE OF EXPLOSION AT UNIT 3?

Does anyone have a source for seismographic recordings at the time of the explosion at Unit 3? If so, it may be an objective way to assess the size of the explosion relative to, perhaps, the explosion at Unit 1.

see post #817 and following.

 

[Azby]

Brilliant idea! I am very curious.

In reply to myself and clarification regarding the translation, this sentence implies that the radiation will be released intentionally and not unintentionally (due to a consequence of some event that might happen) on the 8th May.

I deduce that he is referring to opening the Unit 1 airlock as part of installing the air filter system, as shown on the repair schedule posted earlier. See slide 16 of "Improvement of the environment within the Reactor Building of Unit 1," released by TEPCO onMay 4, 2011

 

[yakiniku]

I deduce that he is referring to opening the Unit 1 airlock as part of installing the air filter system, as shown on the repair schedule posted earlier. See slide 16 of "Improvement of the environment within the Reactor Building of Unit 1," released by TEPCO onMay 4, 2011

Would opening the airlock of unit 1 release sufficient radiation that it may raise concerns such like those when radioactive water was released to the sea?

 

[Azby]

Would opening the airlock of unit 1 release sufficient radiation that it may raise concerns such like those when radioactive water was released to the sea?

That's a good point, of course. I'm just looking at the other slides like "Monitoring of Radiation Dose when opening the airlock to implement the work" and "Environmental Impact Assessment caused by opening the airlock to implement the work," and sensing that the officials are covering their hindquarters with the anouncement. Plus the "opening of airlock" is the only thing marked in red on the schedule!

Of course I hope it's nothing worse than this...

Original attachment (I've retitled it):

 

[AntonL]

@Jorge Stolfi

somehow we missed the following correction by tepco of 24 April, this explains the 10 fold fall of the radiation in torus of unit 3. Maybe you can correct your graphs accordingly when time is on hand

I think we cannot say often enough thanks for your studious work in updating the graphs, I certainly would not have the commitment and patience to do this, so again my many thanks.

[PLAIN]http://k.min.us/inrwQs.JPG

 

[triumph61]

Inside Unit1

 

[rowmag]

Updated sub-drain isotope measurements through 5/3:
http://www.tepco.co.jp/cc/press/betu11_j/images/110503o.pdf

(For criticality-watch fans.)

I guess the only one going up is the unit 3 sub-drain. Iodine increase seems to slow down, but Cs isotopes are increasing. So, what does that change in the ratio of Iodine vs Cesium mean?
I.e. recriticality or just the slow inflow of more contaminated water with Iodine starting to decay away?

As the experts have pointed out, it is a complicated situation with water from different sources being mixed and added to and drained from at various rates, and with various transport and filtering mechanisms in play, in some configuration that is not well understood because it is all happening underground and out of sight... BUT, what I am naively hoping to see is that the long-term trend of the I-131/Cs-137 ratio is going down. There seem to be hints that Unit 2 and/or Unit 3 is making at least sporadic efforts to be difficult (from a simple-minded reading of these plots, and with no knowledge of typical measurement errors).

And here's the sub-drain isotope update through 5/5:
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110505e13.pdf

 

[AntonL]

Reactor 3 temperature still rising, no effect of increased water rate.
two sets of readings 24 hours apart

[PLAIN]http://k.min.us/ikV8Jg.JPG

http://www.tepco.co.jp/nu/fukushima-np/f1/images/00_05050600.pdf
http://www.tepco.co.jp/nu/fukushima-np/f1/images/00_05060600.pdf

The Tokyo Electric Power Company, which operates the damaged nuclear power plant in Fukushima, says it has increased the cooling water flowing into the Number 3 reactor after an increase in temperature occurred over the past week.

On Wednesday, TEPCO increased the flow of cooling water from 7 tons to 9 tons per hour for the Number 3 reactor. The temperature at the bottom of the reactor was 143.5 degrees Celsius at 11 AM on Thursday, about 33 degrees higher than Wednesday last week.

TEPCO has been using temporary pumps to inject cooling water into reactors Number 1, 2 and 3. Their fuel rods are believed to have partially melted down after the tsunami disrupted normal cooling functions.

The operator says the temperature rise was apparently caused by a temporary decline in the amount of cooling water flowing into the Number 3 reactor.

TEPCO increased the amount of water of flowing into the Number 1 reactor for 2 days starting on Wednesday last week, the day when the temperature of the Number 3 reactor began to rise. The company says it continues to carefully monitor temperature changes.
Friday, May 06, 2011 07:29 +0900 (JST)

and has increased to 162^oC by Friday morning 06AM, but tepco also refrains from mentioning that the RPV bellow seal temperature has increased by some 116^oC in the same period

 

[pdObq]

The generic BWR design has two blowout panels on the refueling floor. They are ddesigned to open at low pressures (inches of water) during steam leaks or breaks or during negative pressures such as a tornado. The idea that they would most readily blow out in an explosion does not take inertia into account. A very rapid pressurization (explosion) does not give the panel enough time to move out and open the vent path before overpressurizing the remainder of the walls. In short the blowout panels are not useful during a hydrogen explosion.

Thanks for your answer. I know that you are essentially an expert on these things, but IMHO maybe the "slow" panels you are referring to are different ones. Also, do you have some reference about there being two of those slow popout panels in generic BWR designs?

I still think that proper blowout panels as in unit 1 are useful during an explosion and not during a slow pressure increase. Here is what wikipedia (http://en.wikipedia.org/wiki/Blowout_panel#Blowout_panel) says about "blowout panel" and where they are usually used:

Blowout panel

Blowout panels, also called blow-off panels, areas with intentionally weakened structure, are used in enclosures, buildings or vehicles where a sudden overpressure may occur. By failing in a predictable manner, they channel the overpressure or pressure wave in a direction where it causes controlled, directed minimal harm, instead of causing a catastrophic failure of the structure. Blow-off panels are used in ammunition compartments of some tanks to protect the crew in case of ammunition explosion, turning a catastrophic kill into mere firepower kill. An alternate example is a deliberately weakened wall in a room used to store compressed gas cylinders; in the event of a fire or other accident, the tremendous energy stored in the (possibly flammable) compressed gas is directed into a "safe" direction, rather than potentially collapsing the structure in a similar manner to a thermobaric weapon.

Blowout panels are installed in several modern tanks, including the M1 Abrams and T-80, and have in the past been considered as a possible solution to magazine explosions on battleships.​

​

[red parts highlighted by me]​

So, more expert knowledge and/or opinion would be highly appreciated.

 

[pdObq]

http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/povray/blueprint/foto/drone/hcrop/reactor2-W-1.png
http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/povray/blueprint/foto/drone/hcrop/reactor4-W-2.png

Those are from the great Air Photo Service set. Bot are views from East looking West. The East blow-out panel in #4 is the fourth from left, second from top. Note the clean edges.

Thanks for the pictures. Ok, so the upper building structure of unit2 is the same as 3&4, but different from unit1. Is there basically one slow popout panel (different name to distinguish these panels from the fast blowout panels used for unit1) on the E side and one on the W side? From the fact that the unit2 popout panel just fell down vertically, it seems it really just popped out due to a slow pressure increase. Seems like there was some change in philosophy between unit1 and units234 roof structures.

This is what I understood from what you mentioned a few weeks back. But, (and this is pdObq question) to your knowledge
Was the design of the UNIT 1 meant to be weak permissive for explosion on this floor to be less damaging to the containment bellow ?

Yes, that's exactly my question. Thanks.

yes unit 1 is different, 2,3,4 have one blow panel on the turbine building side, you can see it for unit 2, also there was some ir image posted here where those blow panels were visible. Unit 1 reactor hall wall and roof is the same like 2,3,4 roof, steel construction with concrede without steel in concrede, 2,3,4 construction is concrede with steel rods inside (http://en.wikipedia.org/wiki/Reinforced_concrete)

I don't think unit1 upper wall panels are from concrete, but rather are some sort of steel panels just as on the roofs, see the quote from an earlier post of rive below. Otherwise, I agree.

U1 had no concrete over the service floor: the wall panels were steel, screwed (?) to the steel pillars. U2 - U4 has concrete pillars and concrete panels. My bet is that the destruction could be less severe without concrete, even with the more powerful reactors inside. But I don't know.

By the available pictures some reactors in the US (with MK1 containment - I've looked only for those) has pure metal upper parts. I'll check tomorrow.

Thanks, I am looking forward to your findings.

 

[unlurk]

unable to find anything above 4.0.

Do you have a link to the Japanese language site?

The hydrogen blasts are probably going to show up below 2 on the Richter scale.

 

[MadderDoc]

In reply to myself and clarification regarding the translation, this sentence implies that the radiation will be released intentionally and not unintentionally (due to a consequence of some event that might happen) on the 8th May.

I wonder if this might have anything to do then, with the planned flooding of the containment of unit 1? Tepco is having a hot potato in unit 1, has done all the forework, and quote Tepco, 'the plan could bring the unit to cold shutdown within days.'.

I don't know what is to be expected during such a fast transition of the conditions inside the containment and the rpv, but I imagine it might involve the need to do some venting.

Any current airmass that is inside the containment now would be to some degree steam. With a fast cooling, this steam would condense out, leaving behind other gaseous species in up-concentrated form within containment and pressure vessel. I'd expect those gaseous species to include nitrogen, hydrogen, isotopes of noble gases (some of those radioactive), but hopefully not oxygen.

 

[Bandit127]

I wonder if this might have anything to do then, with the planned flooding of the containment of unit 1? Tepco is having a hot potato in unit 1, has done all the forework, and quote Tepco, 'the plan could bring the unit to cold shutdown within days.'.

I don't know what is to be expected during such a fast transition of the conditions inside the containment and the rpv, but I imagine it might involve the need to do some venting.

Any current airmass that is inside the containment now would be to some degree steam. With a fast cooling, this steam would condense out, leaving behind other gaseous species in up-concentrated form within containment and pressure vessel. I'd expect those gaseous species to include nitrogen, hydrogen, isotopes of noble gases (some of those radioactive), but hopefully not oxygen.

Do we know if the bottom of the RPV is still dry on the containment side? If so, we might expect it to be very hot.

Different people have different views on the current extent of fuel rods melting.I suspect that, if the reactor cores are still contained in the pressure vessels, melted fuel rods are now boiling at over 2,000 degrees Celsius inside an egg-shape crust measuring 4 meters in diameter and 2 meters in height.The crust should be around 20 – 30 centimeters now.

Dr. Michio Ishikawa, Chief Adviser(Former President & CEO)
Japan Nuclear Technology Institute(JANTI)
http://www.gengikyo.jp/english/shokai/Tohoku_Jishin/article_20110413.htm"

I suggest that cooling the hot RPV is going to create a lot of steam, and that could be what they are expecting.

I may be way off here and stand to be corrected.

EDIT - clarified the question about the RPV being dry on containment side

 

[Jorge Stolfi]

I took another frame of the TBS/JNN feed and drew some [black] lines
looks OK to me

What we see here are the West and South faces of building #4. Check the close-up pictures:

http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/povray/blueprint/foto/drone/hcrop/reactor4-E-3.png

The North face was quite deformed by the explosion, the Northwest corner is quite deformed and from a distance it will seem to be tilted.

Moreover the camera does seem to be slightly tilted. Here in green are my guesses as to the true vertical and horizontal lines (below left). Also note that the camera sems to be quite a bit higher then the buildings, so the top part of unit 4's outline is the top of the West wall on the left, and of the East (not South) wall on the right. Both slant down to the right in the image, due to the camera's tilt added to the prespective effect.

Note that the top edge of the North wall and the top of the East wall near Northeast corner are not visible because they are hidden by a large piece of dark gray debris, that sticks out of the roof and blends with the sky in the grabbed frame. I have drawn in pink (below right) what would have been the outline of the building before the explosion.

[PLAIN]http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/povray/blueprint/foto/misc/inqMBW-e.jpg[PLAIN]http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/povray/blueprint/foto/misc/inqMBW-f.jpg

 

[Jorge Stolfi]

@Jorge Stolfi

somehow we missed the following correction by tepco of 24 April, this explains the 10 fold fall of the radiation in torus of unit 3. Maybe you can correct your graphs accordingly when time is on hand

Yes, thanks; I just saw TEPCO's errata sheet that someone recently posted on this thread. It was a 100 fold fall btw. I plan to fix the plots later today.

(Several days ago I tweeted @tep_co about the CAMS drop and got back a reply that they would look into it "later". It seems that they had someone check all their past faxes for transcription errors...)

 

[dh87]

Could that much steam be generated from H2 + O2 ? The interior space of floors 3-4-5 is somewhat less than 30,000 m^3. Wikipedia says that explosion can happen with H2 concentration from 4% to 74%. If we take 40% (max that will burn anyway), that would be at most 12,000 m^3 of H2, which after the explosion would would become 12,000 m^3 of hot steam, which at atmospheric pressure would expand adiabatically to ... huh ... (end of my physics).

Anyway, 12,000 m^3 of H2 at 1 bar ~ 1000 kg of H2 <--> 9000 kg of H2O So the maximum H2 explosion assumed above would generate a mushroom comparable to that of the explosion of a boiler with 9 m^3 of liquid water, overheated to some temperature TBD. Is that compatible with your experience?

However for this maximum scenario we need 9 tons of water combining with zirconium (in the core, in the SFP, or both) to produce that 1 ton of H2. Is this reasonable?

If we take the lower figures, we get perhaps 20,000 m^3 of space filled with 4% H2. That means less than 70 kg of H2 <--> 630 liters of liquid water. That seems more reasonable as far as H2 generation goes; but would it yield enough steam for the mushroom we saw?

If we cannot match the amount of H2 likely to have been produced with the size of the mushroom cloud, two other possibilities are an explosive rupture of the RPV (several tons of superheated water there), or a criticality in the SFP (vaporizing some of the water).

The reaction is 2 H₂O + Zr --> ZrO₂ + 4 H₂. For your high end estimate, making 1e+06g of H₂ requires (1e+06g/2g/mole)/4*91g/mole = 11e+06g Zr. This seems like a lot of Zr available for oxidation since only the surface Zr is immediately available, if I understand the chemistry correctly. The low end is probably too low because the escaping hydrogen will fall below 4% and won't explode, whereas there were explosions in the escaping material.

 

[razzz]

http://atomicpowerreview.blogspot.com/"

 

[zapperzero]

Malfunctioning RHR valve in Kashiwazaki-Kariwa NPP

http://www.monstersandcritics.com/news/asiapacific/news/article_1637433.php/Tokyo-Electric-says-valve-at-nuclear-plant-not-working-properly

EDIT: I thought this interesting because some RHR systems at Fukushima Dai-ni were broken also post 3-11.

 

[elektrownik]

http://www.tepco.co.jp/nu/fukushima-np/f1/images/00_05061300.pdf
#3 243C water level decreasing
#2 torus 130Sv/h
#1 Water injection now 8m^3/h

What else can it be with #3 ? I see 2 options: recriticality or bigger crack/leak in RPV...