Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[PietKuip]

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?

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.

 

[Rive]

Right, exactly. A cumulus cloud needs no barrel, it has direction 'up' due to gravity and it has considerable lifting properties. So why invoke a need for a barrel in the case of the unit 3 cloud?

There was some really big pieces in that cloud, which cannot be explained by just lifting by heat.

Ps.: regarding that radiation spike in the safe bunker: is there even a direct view from the bunker to U3 service floor? To the depths of SFP?

 

[|Fred]

Concerning SFP's and plugs,

The SFP plugs as quoted in the service floor paper are the removable wall making a "channel" from the core to the SPF.

 

[MadderDoc]

Look at this video of US soldiers blowing up a jungle cocaine factory,

Pillar and mushroom development after a small scale military explosion
http://topdocumentaryfilms.com/cocaine-submarines/
[PLAIN]http://k.min.us/in6Hxg.JPG

Yes, pillar and mushroom development is not per se a signature of steam explosions. A good sized fireball (or steamball) and it is set to go.

concerning lifting capacity, all held up by air being a couple of degrees warmer
[PLAIN]http://www.abqballoonrides.com/images/2008_NJFOB.jpg[/QUOTE]

A hot air balloon is usually operated at between 100 and 120^oC and will then produce a lift of about 3 N/m³. The lift of hot water vapour is about double of that, more than 6 N/m³. This is mainly because water has a much lower molar mass than atmospheric air. For comparison one of the best buoyancy gases we have, helium, has a lift of about 10 N/m³. IOW water vapour has over 60 % of the lifting capability of helium.

 

[pdObq]

Could this explain the big hole above N°3 SFP, and maybe some big chunks of concrete thrown in the air?

Apparently they don't use the concrete shield plugs for the SFPs although those seems to exist (see posts a few pages back). (Still waiting for comments on this issue from those with first hand nuclear plant experience... just a reminder, not being impatient )

But what you write could have applied to the dryer-separator pool. Its shield plugs are much heavier than the SFP ones, and they might have put them in place just to have more floor space available. Maybe that could be related to the heavy floor damage in the NW corner of unit 3. Otoh, although we know there is steam venting from the side of the concrete blocks separating the DS pool from the reactor well, those blocks themselves seem undamaged.

EDIT: See post https://www.physicsforums.com/showpost.php?p=3299661&postcount=7054 which came up while writing this. That would make sense, as they are supposedly rather light. But do you know for sure, any documents where that's stated (might be in the whole document, I just looked at the two extracted pages so far)?

 

[pdObq]

A hot air balloon is usually operated at between 100 and 120^oC and will then produce a lift of about 3 N/m³. The lift of hot water vapour is about double of that, more than 6 N/m³. This is mainly because water has a much lower molar mass than atmospheric air. For comparison one of the best buoyancy gases we have, helium, has a lift of about 10 N/m³. IOW water vapour has over 60 % of the lifting capability of helium.

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?

 

[AntonL]

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?

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

 

[whoswho69]

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

 

[pdObq]

The question of putting water in the pools at night has come up several times before. But the official updates give times for pumping & spraying at various pools, and these times indicate that it is extremely rare for any of this stuff to be done during hours of darkness.

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.

 

[MadderDoc]

There was some really big pieces in that cloud, which cannot be explained by just lifting by heat.

Perhaps not, but I think no one has suggested it could. However water vapour .. for a rough estimate, 1 ton of water vapour can produce a lift of 10000 N, the force needed to lift a 1 ton heavy object. If vapour from flash boiling of the sfp should be responsible we can put an upper bound to its capabilities, seeing that a 110C superheated sfp can flash boil at most 30 tons of water. My point is exactly, that we appear to have seen in the explosion significantly more than a sum total of 30 ton of those pieces lifted up and away. So if not enough water vapour could have come from the sfp, we might look for another, potentially larger source. And that source could only be the water contained in the reactor PV and CV. If that source is also not enough, well, then I guess I would have to start taking the criticality issue op to more serious consideration.

 

[jlduh]

There was some really big pieces in that cloud, which cannot be explained by just lifting by heat.

I share this view: due to the size of the big chunks thrown away (some fall on the north side, some on the south side, coming both from the big vertical dark cloud which is coming from the center of the buiding, impossible to be precise at a few meters though) i have a hard time imagining that it can be lifted so high by very warm air...

That's why i only see the gun and barrel explanation really possible IMHO.

 

[pdObq]

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

Well, sure it might be anything (but it looks like it is breaking apart "in flight", and it looks as if it is reasonably heavy), but that is not really my point. I just don't think that stuff is surfing on hot gas, it has been launched by some explosion and is essentially some kind of projectile.

 

[artax]

I'm sorry Anton, but we're simply talking density here, roof sheets would have been carried with the wind much more than that piece that came straight down back on the building. That piece has to be many tons.

 

[jlduh]

1 ton of water vapour can produce a lift of 10000 N, the force needed to lift a 1 ton heavy object.

Well, you have also to consider the height at which this can be lifted, and the speed...

These big chunks that are for sure heavier than 30 tons have been lifted to something like 300m or more...

Even if it's difficult to see exactly which altitude they reached, we have the impression from the ballistic trajectory that they were not so far from the top of the dust cloud . So if dust is lifted by steam (warm air) at a certain height, it is not conceivable that this height minus a certain percentage (let's say 15% less height visually) can be achevied by the same process (warm air lifting) for very heavy objects like the big chunks. If these big chunks go so high, it's because they gained cinetic energy (1/2 mv2) right after the explosion, which implies very high speeds of ejection in the first moments of explosion.

That's the principle of a bullet: to go far you have to go very quickly at the start. The warm air (quick volume expansion) is only efficient in the tube of the gun to create big acceleration, then the bullet uses it's stored cinetic energy to continue its travel.

Light dust can be lifted by steam but it's a different process (thermodynamics and aerodynamics).

Even if you see big heavy chunks AND dust+steam going in the same direction at almost the same height, the physical and mechanical processes and laws involved are of different nature (more precisely all the laws are applied to both of them but in various contributions to the end results, depending on their own physical properties).

I think some are getting mislead by visual (wrong) evidence comparing the two.

 

[pdObq]

Both images are taken from this Caltech presentation: http://www.galcit.caltech.edu/~jeshep/fukushima/ShepherdFukushima30April2011.pdf

According to these images, it's normal under emergency cooling conditions that the Drywell in Units 2 and 3 is filled with hot steam.

Those attached images from that presentation suggest that the RCIC steam turbines and releated equipment is located in the north side more or less below the DS pool. That of course is a very simplified drawing, and they might be actually located in other places of the buiding.
But it points me again to that large damage on the NW corner of unit 3. If there was a direct steam line from the reactor going there, and there was overpressure or earthquake related seal damage, then H2 might have accumulated there (among other places).

Alternatively, if there was sudden overpressure within the reactor the path of least resistance would be through the steam lines into the RCIC turbine...

 

[|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.