Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[|Fred]

http://www.fairewinds.com/updates - Arnold Gundersen

I'm glad that he corrected a couple inaccuracy he made in the past (2km not 2 miles, etc).
I think he is mistaken on the U4 leaning theory because he did not saw the latest picture.

 

[TCups]

And say, don't I remember a passive emergency cooling system that operates without electric power driven by a steam turbine that circulates through a cooling pool? Was such a mechanism in operation at Unit 3? Would that have been in any way related to heating SFP3 (ie, was initial emergency cooling of the Unit 3 core at the expense of additional heating of SFP3 or is another water reservoir used for this emergency system, if it was used)?

Ah, yes, here: https://www.physicsforums.com/attachment.php?attachmentid=35514&d=1305281756PS: Thank you for the previous edit, Borek. Sorry that my lack of facility with multi-quotes required the extra effort for you.

PPS: Thank you clancy for the reference added as an attachment to post 7035, here:
https://www.physicsforums.com/showpost.php?p=3299553&postcount=7035

 

[artax]

Does anyone have a link to a slo mo video or the still frames of the unit 3 explosion, I've just been watching it and there's a lot of info in there.
T cups has analysed it in detail... I just haven't had a good video till the one I posted last page. And I've just realized you can almost go frame by frame by double clicking on youtube.

Anyway there is definitely a release of flammable gas out of the east (or SE) of the building which then ignites... and this happens BEFOERE the south facing wall disintegrates! There's also a frame in there that seems to show the south wall bulging out,... while the orange flame is diminishing befoer the second (big) explosion.
I wish I had gone with you a few hundred pages back... Tcups!

watch from 14secs: here:- http://www.youtube.com/watch?feature=player_detailpage&v=RxAHoxEvv7Y#t=16s

Fascinating stuff

 

[pdObq]

I think he is mistaken on the U4 leaning theory because he did not saw the latest picture.

It's funny that he is picking that up at all...

 

[jlduh]

Does anyone have a link to a slo mo video or the still frames of the unit 3 explosion, I've just been watching it and there's a lot of info in there.
T cups has analysed it in detail... I just haven't had a good video till the one I posted last page. And I've just realized you can almost go frame by frame by double clicking on youtube.

Anyway there is definitely a release of flammable gas out of the east (or SE) of the building which then ignites... and this happens BEFOERE the south facing wall disintegrates! There's also a frame in there that seems to show the south wall bulging out,... while the orange flame is diminishing befoer the second (big) explosion.
I wish I had gone with you a few hundred pages back... Tcups!

Fascinating stuff

I confirm what you say, i analysed this stuff very accurately and the flash out of the building implies that some gas (already inflammed or not) have to escape the building BEFORE the walls are destructed.

The flash is then going "off" and then the explosion comes with destructions.

EDIT: here are the links to frame by frame explosions at N°1 and N°3 (i think this is what you were looking for Artax):

http://gyldengrisgaard.dk/fuku_expl1/
http://gyldengrisgaard.dk/fuku_expl3/index.html

talking about "bulging, look closely at the frames -4 to +2 on the N°3 reactor page. To me you can actually see the south wall of the building "bulging" under internal pressure like a Coke can just before ignition and explosion (look at faint shadows, the sun position seems to help to see this)...

This is even more fascinating. These stronger walls (than N°1) have had maybe an important role in what happened, enabling higher pressure inside building before cracking...

 

[Astronuc]

Something to mull over.

http://www.world-nuclear-news.org/RS_Water_poses_questions_for_Tepco_1205111.html

In the last two weeks the temperature of unit 3 has gradually risen from around 90ºC to around 210ºC. It is not known if this is related to the water leak.

Meanwhile at unit 1 the return of workers to the reactor building interior seems likely to lead to revelations about the true state of the core. Tepco has installed and calibrated one of two new water level gauges, finding the level to be below what was previously thought. This led to speculation that the entire reactor core may have been exposed for long periods of time, with the increased chance of serious damage.
. . .

Eslewhere I read that material from the core of unit 1 has dropped into the bottom plenum of the RPV.

 

[pdObq]

The newspaper article says about this bunker:
"The three-story, white bunker had extra-thick walls and two filtration systems designed to keep out radiation."
http://www.bloomberg.com/news/2011-04-25/japan-s-terrifying-day-saw-unprecedented-exposed-fuel-rods.html

An earthquake-proof radiation shelter. Yet the radiation spike was measurable inside.
To me this is rather strong support for Gundersen's theory.

My personal opinion is that there has been no criticality in any of the SFP pools. At least I haven't seen enough evidence to believe in that.

However, what if there was recriticality in unit 3 reactor core? Would it be conceivable that after the fuel rods have been without sufficient cooling (above water level), they start heating up, melting away the control rods (borated steel, would it melt prior to the fuel pellets?), then they start injecting cooling water from outside, which cools the remains, but also acts as moderator. With control rods partly gone, the core suddenly goes critical, followed by essentially steam explosion within containment, which however, is not strong enough to destroy the drywell, but causes the spectacular explosion of unit 3 reactor building including gamma spike?

 

[jlduh]

Does anyone have a link to a slo mo video or the still frames of the unit 3 explosion, I've just been watching it and there's a lot of info in there.
T cups has analysed it in detail... I just haven't had a good video till the one I posted last page. And I've just realized you can almost go frame by frame by double clicking on youtube.

Anyway there is definitely a release of flammable gas out of the east (or SE) of the building which then ignites... and this happens BEFOERE the south facing wall disintegrates! There's also a frame in there that seems to show the south wall bulging out,... while the orange flame is diminishing befoer the second (big) explosion.
I wish I had gone with you a few hundred pages back... Tcups!

watch from 14secs: here:- http://www.youtube.com/watch?feature=player_detailpage&v=RxAHoxEvv7Y#t=16s

Fascinating stuff

To complete my post above, i extracted the frame you are talking about showing the bulging of south wall just before disintegration. On the link i gave this is frame n°1, but you can see the process starting in the frames just before. The bulging seems to be 3 floors high, which is consistent with the destructions on the building N°3. You see also that the flash is already ignited outside, and expanding. I don't have an explanation why the destructions seem to start at the periphery of the the south wall (the black lines of concrete/dust ejected (i think ?) along the roof and on the right side of the wall). To me it just indicates that these walls were strong and that the first cracking path (path of least resistance) would be there, at the periphery, which is consistent with some gases released at the top south east corner of the structure and creating the flash.

http://gyldengrisgaard.dk/fuku_expl3/index.html

http://www.netimago.com/image_199656.html:

http://www.netimago.com/images/qDOtRM98dbnL1E0.jpg

 

[pdObq]

EDIT: here are the links to frame by frame explosions at N°1 and N°3 (i think this is what you were looking for Artax):

http://gyldengrisgaard.dk/fuku_expl1/
http://gyldengrisgaard.dk/fuku_expl3/index.html

[...]
This is even more fascinating. These stronger walls (than N°1) have had maybe an important role in what happened, enabling higher pressure inside building before cracking...

Ah, so let's get back to discuss this https://www.physicsforums.com/showpost.php?p=3285013&postcount=5896 , see also https://www.physicsforums.com/showpost.php?p=3287586&postcount=6055 and my personal conclusion https://www.physicsforums.com/showpost.php?p=3287854&postcount=6069 .

Unrelated from that, those snapshots are nice. Assuming it's the same camera from the same spot as the TBS/JNN live feed, then unit 4 pre-fire/explosion did not appear to be crooked. So, even if it is an optical illusion it is probably not from the camera or optics, but from the building.

[EDIT2: Careful with these frames, they only show an integral over what happened within 1/25 s, faster dynamics will appear washed out.]

 

[TCups]

I confirm what you say, i analysed this stuff very accurately and the flash out of the building implies that some gas (already inflammed or not) have to escape the building BEFORE the walls are destructed.

The flash is then going "off" and then the explosion comes with destructions.

EDIT: here are the links to frame by frame explosions at N°1 and N°3 (i think this is what you were looking for Artax):

http://gyldengrisgaard.dk/fuku_expl1/
http://gyldengrisgaard.dk/fuku_expl3/index.html

At the risk of again being redundant again, yes. The VISIAL evidence is what led to all of my initial speculation about the vector of the blast and its origins from the region of the fuel transfer chute. The additional clues -- information about the drywell cap seal, and the fuel transfer chute seal followed.

Initial general speculation regarding the explosion at Unit 3 was that such an energetic blast could only arise from the RPV, yet the RPV pressure was initially preserved. How could that be?

A lot of visible thermal energy is released BEFORE the entire building explodes and the steam explosion occurs. It appears at a very specific location and in a very specific vector, through the southeast end of the building, from, or over the SFP3.

The ignition and conflagration of the initial ejected gas cloud appears to me to occur after it has, like Elvis, left the building. The explosion of the entire building appears to follow the external ignition, and the rising steam column is the last event.

And if you choose not to dismiss the audio evidence, there are also clearly two and possibly three distinct explosions, depending on how one interprets the data (M. Bachmier has done extensive analysis on this).

MaderDoc's analysis of the roof damage supports this scenario, IMO.

In retrospect, is there anything like the bright blue flash that might be expected with a sudden criticality on that video? To my eyes, no. The "sudden" event is the initial outward blast of a cloud of white gas then a fireball at the SE corner.

@MadderDoc:
Sir - might I respectfully ask if you might consider turning your talented eyes toward the south end of Building 3 and perhaps adding your assessment of the mechanical and thermal damage to the south end of the building as well as the roof? I believe you may find similar evidence that the initial blast and thermal damage had a substantial horizontal vector as well. Thanks.

 

[rowmag]

The newspaper article says about this bunker:
"The three-story, white bunker had extra-thick walls and two filtration systems designed to keep out radiation."
http://www.bloomberg.com/news/2011-04-25/japan-s-terrifying-day-saw-unprecedented-exposed-fuel-rods.html

An earthquake-proof radiation shelter. Yet the radiation spike was measurable inside.
To me this is rather strong support for Gundersen's theory.

Ok, here is some information you may be interested in. Apparently TEPCO has released some previously-unreleased internal notes on what was happening in the early days. Fascinating reading, published in today's Asahi Shimbun (paper edition). A couple highlights (bolding mine):

"3/12 10:17 Unit 1 venting starts." Has to be done manually, because can't get electricity working in time. One worker takes over 100 mSv in the operation.

"3/12 11:31 Unit 1 water level drops to 1 m below top of fuel."

Followed by some confusion about whether the venting actually worked or not, then...

"3/12 15:36 Sound of explosion at Unit 1"

"3/12 15:45 1 mSv/h measured at 1st floor of seismic bunker, 180 micro-Sv/h inside, several people injured."

"3/12 18:30 0.07 micro-Sv/h neutrons confirmed between North Gate and West Gate (possibility of criticality accident)"

Also, they were planning to open the blow-out panel on Unit 2, but then discovered that it had already happened by itself.

Would be interesting to find the whole thing. Not posted on Asahi website that I see.

Add: Someone has posted a photo of the story printed in the paper:
http://www.geocities.jp/swingi70/_gl_images_/P1020249toudenn.jpg

 

[SteveElbows]

It's funny that he is picking that up at all...

And how come he says that TEPCO has confirmed the leaning at 4? I don't recall them doing any such thing, is this simply more Gundersen sloppiness with facts, or have I missed something?

In any case it seems reasonable to claim that some specific parts of certain walls at reactor 4 may be leaning slightly, but the claim that the whole building is leaning still lacks credible evidence.

 

[artax]

Something to mull over.

http://www.world-nuclear-news.org/RS_Water_poses_questions_for_Tepco_1205111.html

Eslewhere I read that material from the core of unit 1 has dropped into the bottom plenum of the RPV.

Very interesting... I also read earlier today that "there is likely a few cm hole in the RPV [unit 1] from where the water is leaking" or words to that effect... I'll have a look for it, I was reading the latest Guardian report... then followed a few links I think.!

there's a different report here:-

http://www.reuters.com/article/2011/05/12/japan-nuclear-reactor-idUSL3E7GC2JQ20110512

it still amazes me that they aren't in the relatively desirable situation of having just one Nuclear Reactor Meltdown to work on but THREE!

Hey Tcups/Jlduh... is it possible that the hydrogen was building up UNDER PRESSURE inside a contained vessel... that vessel failed to air, then ignited due to a source outside... and then flashed back to ignite the hydrogen in the building/vessel? The flame does seem to suck back towards the building itself. I'm not suggesting the pressure vessel here.

 

[RealWing]

REGARDING THE HIGH SPIKE OF MEASURED RADIATION ASSOCIATED WITH UNIT 3'S EXPLOSION


Could there be another plausible explanation? For example:

Could the spike in measured radiation levels be explained by the explosive release of volatile iodine and cesium (or other highly radioactive isotopes) from the explosion and venting of the contents of the drywell of Unit 3, lofted by the associated steam flash? I believe there were smaller spikes in measured radiation during controlled venting. It would seem to make sense that explosive venting would be a much larger spike.

Could some of the contents of SFP3 also have been damaged by an explosion and steam flash and also lofted and scattered, perhaps also contributing to the spike?

TCups - I'm with you on this one. As I indicated before - it looks like simple gamma shine from the cloud of radioactive material as you suggest.

 

[MadderDoc]

But you don't want to imply that those large concrete chunks thrown upwards in the explosion are floating on some kind of hot gas?

Believe it or not, such a chunk in free fall in air would have a terminal velocity of about 90 m/s, and during the first few seconds of the evolution of the mushroom cloud, it expanded upwards at higher than that speed. So, certainly during this phase a large concrete chunk placed in the rising column would seem to be floating on some kind of hot air. It would be unable to fall down, and would rather be propelled upwards.

But that said, at take off, initially, these chunks could of course not have been propelled upwards by the rising airmass, and later, when the upwards speed fell below the terminal velocity, the updraft could at most aid to prolong their upwards journey.

However, what I am talking about starts out with a breach in a primary containment full of hydrogen and hot water and steam under pressure. When a breach happens under such conditions, you will likely first see the hydrogen igniting at expulsion, but then things will quickly develop into what is technically called a "boiling liquid vapor expansion explosion", when large quantities of the superheated liquid, in this case water, at the initial pressure drop due to the breach almost instantaneously flashes into vapor within the confined space of the containment vessel. This will produce an extremely high pressure within the vessel, and an ensuing violent explosion. When this happens objects large and small will naturally be hurled out and away at high speed.

 

[|Fred]

And how come he says that TEPCO has confirmed the leaning at 4?

Nah this is a twist .. Tepco says something like we need to watch the wall because they may be unstable and they were likely reffering to the north wall and part of the souther eat wall etc because of the way the "blast" destroyed some of the structure.

And just like Nancy, Mr fair wind take this statement and put it in the context of the leaning theory. Its close to a syllogism: Tepco fear some walls may be unstable, + I see a wall leaning south = Tepco confirm the my wall is leaning South

 

[PietKuip]

And how come he says that TEPCO has confirmed the leaning at 4? I don't recall them doing any such thing, is this simply more Gundersen sloppiness with facts, or have I missed something?

Tepco (in their "plan" or "roadmap") revealed that the stability of the #4 SFP was precarious, and that it was one of their top priority problems. Since then, they have talked about steel pillars filled with concrete to support it.

 

[PietKuip]

Apparently TEPCO has released some previously-unreleased internal notes on what was happening in the early days. Fascinating reading, published in today's Asahi Shimbun (paper edition). A couple highlights:
"3/12 15:36 Sound of explosion at Unit 1"

"3/12 15:45 1 mSv/h measured at 1st floor of seismic bunker, 180 micro-Sv/h inside, several people injured."

"3/12 18:30 0.07 micro-Sv/h neutrons confirmed between North Gate and West Gate (possibility of criticality accident)"

Wow.

But I have never understood their units for neutrons. I cannot interpret it. Thermal neutrons carry very little energy. I would prefer to know a flux, number of neutrons per square meter.

But this seems to indicate that there was a chain reaction outside the biological shield, at the bottom of the RPV.

 

[pdObq]

Believe it or not, such a chunk in free fall in air would have a terminal velocity of about 90 m/s, and during the first few seconds of the evolution of the mushroom cloud, it expanded upwards at higher than that speed. So, certainly during this phase a large concrete chunk placed in the rising column would seem to be floating on some kind of hot air. It would be unable to fall down, and would rather be propelled upwards.

That terminal velocity comes from equilibrium between the force of Earth pulling on it and air resistance pushing agaist it. After those projectiles are launched there is no force onto them any more, only air resistance. The projectiles can sure be faster than that terminal velocity if the force that launched them is large enough. When you place an initially at rest heavy object into that upwards column, that's just like wind flowing around some heavy object. So, I guess from cv value and air speed in the column one can get the force onto that object. (But that is not buoancy (sorry if that's mispelled) or floating as that would imply lower effective density of the floating object.)

EDIT: Ooops, before borek points it out to me, of course, gravity is still pulling on it after the launch... forgot to mention the obvious again...
And I guess, I first misinterpreted your statement. Basically you are saying the column is moving upward at a speed sufficient such that an object at rest would experience a force due to air resistance greater than its weight? But since the big chunks almost move together with the column at first, there should be no air resistance related forces on them then (apart from the big chunks appearing to be mostly outside the dust/smoke column).

 

[swl]

The upper containment building of of unit two was made of light gauge steel panels attached to a steel inner structure.

The upper containment building of unit 3 was constructed of heavy, steel reinforced, concrete.

The No. 3 rebar alone weighed more, and was stronger, than the light steel paneling that was keeping the rain off of unit 1. When considering the fact that the upper containment walls surrounding unit 3 were much heavier, and much stronger than the walls surrounding unit 1, it seem likely that more force, and more material would have been directed vertically rather than horizontally.

And about that dust cloud; when you bust up a bunch of concrete, you usually end up with a bunch of concrete dust and big rocks. It looks like the unit one explosion was mostly expanding gas and light metal panels. Unit three's explosion looks more like a mess at least partially because of the entrained dust and big rocks.

Yeah other factors exist, but please don't discount these differences in construction, along with the larger volume of the upper containment area inside of reactor No 3 and the differences in emergency cooling systems that would have likely resulted in higher temperatures in the suppression pool of unit No 3 at the time of it's explosion.

What do you all think about the differences in the speed that the explosions left the buildings? It only took about 16 frames for the cloud to reach the top of the stack during the No 1 explosion, but on the No 3 explosion it took about 25 frames. Could it be that I simply can't see the shock wave from unit 3 because the outside humidity was lower, or was it a slower moving bang?

One other thing, Gunderson was right; That unit No 3 was promptly turned into a critically big mess by that explosion.

 

[MadderDoc]

@MadderDoc:
Sir - might I respectfully ask if you might consider turning your talented eyes toward the south end of Building 3 and perhaps adding your assessment of the mechanical and thermal damage to the south end of the building as well as the roof? I believe you may find similar evidence that the initial blast and thermal damage had a substantial horizontal vector as well. Thanks.

Certainly. It seems quite obvious to me that the initial blast had a substantial horizontal vector. We can see that in the video already in the very first frame that shows something abnormal is going on in the building.

In this first frame, the flash of fire has not yet risen over the building, of that we see only the top part of some smoke it has produced, at the top east side of the building where the flash of fire presumably first made exit. But concurrently, in the very same frame we see the west face of the building abruptly changing its reflective properties, consistent with its shattering. And, in the next few frames all the walls that are visible in the video appear to collapse, horizontally outwards, quite consistent with how we find wreckage and tracks of grey dust and debris after the event, cast horizontally out to the east, west and south (Indications of a similar horizontal spew at the north end are weaker, due to later events with ballistic objects messing up 'the scene of the crime'.) However, we know that in the NW corner a big machine was situated (I believe for air filtering) before the explosion. After the explosion we find this machine hanging from the wall under the panel where it was situated, apparently defying gravity, but more realistically just hanging on with its ducts and wires. This machine very unlikely could have been moved to this miraculous position by a vertical force, for that feat a horizontal force would need to be present, also at the north end of the building.

 

[jlduh]

More contamination on the grass in towns outside of the evacuation zone, and far outside!

http://www3.nhk.or.jp/daily/english/13_01.html



NOTE THAT NIKKO CITY IS AT AROUND 170 kms FROM THE PLANT (SOUTH WEST) which is quite far... the other one is at around 100 kms same direction.

http://maps.google.com/maps?f=q&sou...8424,140.542603&spn=2.548084,6.696167&t=h&z=8

It seems that the winds are spreading the bad stuff in several directions, the North west has been severely touched, the South West could start to get the same scenario.

Over a long period of time (who knows when this crisis will be contained), we can fear that long life Cs-137 (ans maybe Strontium?) will accumulate here and there, like thin layers of small snow falls which would never melt and add weeks after weeks...

The only difference being this is invisible and dangerous snow...

Some more contamination of tea leaves:

http://www3.nhk.or.jp/daily/english/13_39.html

Radioactive material above designated safety limits has been detected in tea leaves harvested in 5 municipalities in Kanagawa Prefecture, neighboring Tokyo.

The prefectural government checked samples of leaves harvested in 15 municipalities in the region. Officials say that samples from 5 of those were found to contain unsafe levels of radioactive cesium.

They say 780 becquerels of cesium were detected in tea leaves in Odawara City, 740 becquerels in Kiyokawa Village, 680 becquerels in Yugawara Town, 670 becquerels in Aikawa Town and 530 becquerels in Manazuru Town.

Damn, this info is really a breaking news to me, not because of the levels (even it there are sufficiently high to make them unsafe!) but BECAUSE OF WHERE THEY HAVE BEEN MEASURED:

KANAGAWA prefecture is south of Tokyo!

I located Odawara on this map for example:

http://maps.google.com/maps?f=q&sou...008,140.855713&spn=4.754161,13.392334&t=h&z=7

So this is around 330 kms south west of Daichi plant!

Minami Ashigara, also listed in the article, is even further

http://maps.google.com/maps?f=q&sou...0598,139.251709&spn=4.74326,13.392334&t=h&z=7

The scale at which unsafe deposits are falling is enlarging day after day...

 

[jim hardy]

"""However, what if there was recriticality in unit 3 reactor core? Would it be conceivable that after the fuel rods have been without sufficient cooling (above water level), they start heating up, melting away the control rods (borated steel, would it melt prior to the fuel pellets?), then they start injecting cooling water from outside, which cools the remains, but also acts as moderator. With control rods partly gone, the core suddenly goes critical, followed by essentially steam explosion within containment, which however, is not strong enough to destroy the drywell, but causes the spectacular explosion of unit 3 reactor building including gamma spike? ""

similar train of thought explored on this thread, on May 7 i think, its page 314 viewed in Firefox don't know about explorer. Look for two long posts by Analog, and don't miss the videos on Borax.

http://tickerforum.org/akcs-www?post=182121&page=314#new

jorge stolfi - in his second long post the guy bragged on your plots bigtime !

 

[artax]

Yes, very shocking, and I read a while back that the summer winds are usually from the East, but haven't changed yet!

 

[MadderDoc]

<..> Basically you are saying the column is moving upward at a speed sufficient such that an object at rest would experience a force due to air resistance greater than its weight?

Yes, or at least that was what I was trying to express :-) I do not think we can find anything substantial to disagree over in regards to this aspect.

 

[SteveElbows]

Tepco (in their "plan" or "roadmap") revealed that the stability of the #4 SFP was precarious, and that it was one of their top priority problems. Since then, they have talked about steel pillars filled with concrete to support it.

Yes, I noticed that when they first published their roadmap, it seemed to take a while before this detail started getting picked up and discussed in the news. But its not the same as TEPCO saying that unit 4 is leaning. We can tell just by looking at images of the building that's its not in great shape, but that's about it, and all the talk of leaning, sinking etc has driven me somewhat bonkers over the last week. I suppose I should not be surprised at Gundersen joining in, despite the immense horror of what has unfolded at Fukushima it is apparently not enough for some people, especially those with an agenda, who feel the need to hype things up.

Having said that if there was another big quake and building 4 partially collapsed, I would not be shocked, but I am not going to spend much time thinking about it unless it actually happens.

 

[etudiant]

Yes, very shocking, and I read a while back that the summer winds are usually from the East, but haven't changed yet!

What is really shocking is how little useful information about this disaster is available.
For instance, there is still no measurement available, afaik, of the overall daily airborne emissions from the site, even though that should be of central concern. These emissions will likely continue for at least the rest of the year, so their level of radioactivity will determine how large the Fukushima damage zone will be.
There is plenty of detail information, even if it is sometimes wrong, but no context.
The absence of overall perspective, either situationally or visually makes it very hard to get a coherent picture of the effort. This is probably deliberate, but the benefit of this security through obscurity approach is dearly bought. It hobbles any outside contribution and leaves the population in a state of anxious uncertainty.

 

[SteveElbows]

Doh, it seems the pit water at reactor 3 that got in the news recently because it caused sea contamination, was caused by their earlier water transfer operation:

http://www3.nhk.or.jp/daily/english/13_02.html

The company transferred radioactive water from the turbine building of the No.3 reactor earlier this month. It says during that process radioactive water leaked out from an underground pipe connected to the pit.

The company admitted in a news conference on Thursday that prior inspections to prevent leaks were inadequate.

Just how large will the catalogue of errors become by the time this situation is brought somewhat under control?

 

[TCups]

concrete chunks - I would say roof sheets judging by there size

Absolutely roof chunks. Where would there have been concrete slabs over the vertical component of the explosion to be carried upward (unless you believe it to be part of the concrete plug over the reactor)? The concrete was in the walls and blew outward. It was the roof slab (and, IMO still possible, the FHM or parts of it) that went ballistic vertically. I still don't know the exact composition or density of the roof slab of Bldg 3. It was some type of flat slab industrial roofing over corrugated sheet metal over metal roof girders, though.

Either way, I believe something pretty heavy went up and then came down on the northwest corner of Bldg 3, this supported by video evidence, cross checked with the camera angle, and with the resulting damage. The denser, heavier ballistic objects would tend to be deflected less than the lighter stuff, though, and would be what fell on the building.

@MadderDoc
As for the reflectivity and crumbling of the walls, I suspect it was something like that, yes. But it would seem to me that a generalize hydrogen explosion strong enough to do that to reinforced concrete wall slabs would more likely have first blown the roof upward, not the walls outward, as appears to be the case. But that is only a guess. Also to be considered is the shadow that might arise from the initial blast at the southeast corner.

And I forget who asked, if the ignition of hydrogen gas exterior to the primary containment could have ignited not only the hydrogen accumulated in the upper building, but also the hydrogen in the primary containment (and maybe the torus) in retrograde fashion. I don't know but I can't exclude the possibility. My guess would be that as long as the contents of the primary containment were venting under pressure, the ignition would turn it into more of an outward blow-torch effect than a retrograde ignition and explosion going back into the primary containment. I am pretty sure whatever shot out of the primary containment was intensely hot and powerful, though, whether it was "burning" or not.

 

[SteveElbows]

I think someone had the very reasonable explanation that since it is colder at night, the steam condenses more readily, so that it appears as white clouds/fog. Someone else compared it to the cooling tower next to where they live, it strongly depends on the weather whether there is visible condensation of the steam.

Yes. Personally I've seen nothing on the live images this week that could not be explained by weather-related phenomenon.

I mention the information about fuel pool pumping & spraying times only to clarify these details, not because I am searching for an explanation for the varying visible steam on live feed myself. But it seems we are doomed to repeat this discussion nearly every day since the live feed causes new people to get overexcited by what they are seeing all the time.