Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[MadderDoc]

Hello,

Would you be so kind as to provide links to the source documents where you found the photos and the "IAEA map of assembly" ?

The photos are cropped frames from the Tepco survey video at

http://tepco.webcdn.stream.ne.jp/www11/tepco/download/120322_01j.zip

The map of assembly activities is cropped from the document "DOE Response to Fukushima Dai-ichi Accident"

which is included in these transcripts from the US DOE ACRS subcommittee on Fukushima May 26 2011 meeting (the map is on page 188 of those transcripts)
http://pbadupws.nrc.gov/docs/ML1114/ML11147A075.pdf

It must have been just my inference from recollection, that DOE had got the information on the Unit 4 SFP heat generation distribution via the IAEA, and I may be totally wrong, sorry. The document itself says nothing about how the data has been sourced. The original source for such detail of information must of course have been Tepco.

 

[tsutsuji]

Thanks. I had guessed the pictures were from Tepco's videos, but I was not aware about that DOE document.

 

[MadderDoc]

New and quite exciting photos from the spent fuel pool of unit 3
http://photo.tepco.co.jp/en/date/2012/201204-e/120413-01e.html
Pictures are taken close to the cask transfer area, they show upright standing fuel racks, and ..
a fine close up view of an end piece from the rail foot of the bridge that carried the fuel handling machine.

(Here seen compared to a Quince photo of the foot of the quite similar FHM bridge of unit 2

 

[SpunkyMonkey]

New and quite exciting photos from the spent fuel pool of unit 3...

Lol. I just came to post a link to that Tepco release. Great identity spot Maddder! More of you're non-stop top-notch analysis!

I seem to recall just a few weeks ago someone here called that the refueling crane simply fell into the pool (it wasn't blown to kingdom come) based on clues in a photo, but that least-extraordinary thesis was not too well received.

Here's a video clip of what clearly appears to be part of the refueling crane, I suspect it's the upper deck of the trolley. It's also the same object I posted previously, suggesting it looks like the trolley deck.

Here's a video expressing skepticism that the Unit-3 fuel pool exploded, which imo is further supported by the release of photos of fuel racks in SFP3. I think the Unit-3 explosion had nothing to do with the fuel pool, and the pool only suffered from in-falling debris.

 

[jim hardy]

I think the Unit-3 explosion had nothing to do with the fuel pool, and the pool only suffered from in-falling debris.

indeed Arnie's pool criticality hypothesis would have steam-cleaned it and scattered the contents. Instead it's gor rebar pointing in.

Yet in the satellite photo 3 minutes post-explosion it looks to be steaming vigorously.

if that's a correct interpretation of photo it got a lot of heat from someplace.

Last spring I calculated ~10^18 neutrons into Keff of 0.95 would make a thousand pounds of steam
but couldn't come up with a path from core to SFP that doesn't go through a few tenth-value thicknesses of concrete...
so another scheme worthy of Wiley Coyote bit the dust.

 

[hellbet]

Nice catch MadderDoc, it was all but evident to identify the FHM Trolley skating. Looks like one find out FHM3... finally.

 

[SteveElbows]

Yet in the satellite photo 3 minutes post-explosion it looks to be steaming vigorously.

if that's a correct interpretation of photo it got a lot of heat from someplace.

Easy for that to be the wrong interpretation of that photo. Release could be from the edges of the reactor well plugs, not the pool.

 

[SteveElbows]

I seem to recall just a few weeks ago someone here called that the refueling crane simply fell into the pool (it wasn't blown to kingdom come) based on clues in a photo, but that least-extraordinary thesis was not too well received.

Thats largely my fault, but that's because I did not consider the round objects in the photo to be a great match for refuelling bridge pulleys. This didn't mean I ruled out the possibility that the refuelling thing was in the pool, I just didn't think the images presented were good enough evidence. Subsequently someone pointed out a related ladder and I did find a good video showing that, so despite my original negativity about the analysis I was not dead against it.

I hope that when we get to see the video things become slightly clearer, but debris of one sort or another in reactor 3 pool is clearly quite a big problem.

 

[Yamanote]

They also did some investigations on the integrity of unit 4:

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120413_04-e.pdf

 

[tsutsuji]

They also did some investigations on the integrity of unit 4:

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120413_04-e.pdf

Thanks. This is a follow-up of the February measurements. It is good that it is now translated into English.

http://www.tepco.co.jp/nu/fukushima-np/roadmap/images/m120227_05-j.pdf On page 85/94 there are four measurements of the distance between the reactor well water level and the 5th floor's floor in four locations. The measurements show that the floor is horizontal. It looks like the old "unit 4 is leaning" theory is ruled out...

http://www3.nhk.or.jp/news/genpatsu-fukushima/20120413/index.html (survey into unit 3 SFP) the camera was lowered by about 7 m underwater. It was confirmed that part of the fuel handling machine (35 tons) has fallen into the pool. No conspicuous fuel damage was seen on the pictures. As it is dark inside the pool, the photography was not good and only 4 pictures were publicly released. Tepco said "With today's survey we could not understand the details of the situation. We shall perform more surveys so that we can find out the debris distribution and the fuel status, so that we can study a safe fuel removing method."

http://www3.nhk.or.jp/news/genpatsu-fukushima/20120413/1510_teishi.html The nitrogen injection system into units 1,2,3 was suspended this morning for 2 and a half hours shortly after 01:00 AM. It is the 4th time it happens since last month (it previously happened on 12 March, 4 April and 7 April). Tepco is investigating the causes. As a consequence, unit 1's PCV temperature rose by 5°C from 50°C to 55°C from 04:00 AM to 06:00 AM. There was a leak from a joint in unit 4's pool cooling system. 40 liters of water including radioactive substances leaked into the building. Tepco does not know when the pump can be restarted.

 

[SteveElbows]

What is the theoretical mechanism by which the temporary stopping of nitrogen injection leads to an increase in measured drywell temperature? Or has the article made a poor assumption?

 

[tsutsuji]

What is the theoretical mechanism by which the temporary stopping of nitrogen injection leads to an increase in measured drywell temperature? Or has the article made a poor assumption?

A similar causal relationship was mentioned in the document I translated at https://www.physicsforums.com/showpost.php?p=3843299&postcount=12798

I made a translation mistake. The document says "some of the PCV thermometers were displaying a rising trend".

 

[SteveElbows]

A similar causal relationship was mentioned in the document I translated at

Thanks very much. I'd still like to know what the theory behind this trend is.

 

[SpunkyMonkey]

indeed Arnie's pool criticality hypothesis would have steam-cleaned it and scattered the contents. Instead it's gor rebar pointing in.

Yet in the satellite photo 3 minutes post-explosion it looks to be steaming vigorously.

The steam seems to be coming from around the well-cap rim, as was usual after the blast. One of the well-cap steam-ejection spots was right at the North edge of the pool.

This is my best effort to superimpose the floor plan onto the 3-minute-after image.

The satellite images seem to skew square buildings somewhat, so the floor plan is slightly skewed I hope to the best fit. I believe the steam is not coming from the pool but from around the primary containment, as seen in a lot of imagery from the early days.

 

[SteveElbows]

Here's a video clip of what clearly appears to be part of the refueling crane, I suspect it's the upper deck of the trolley. It's also the same object I posted previously, suggesting it looks like the trolley deck.

Certainly the video does show me more interesting detail of the circular objects at the top of the picture than the photo did. A lot of what put me off the previous image was the partly circular object that is further to the left on the images, and can't really be seen at all on the video. I don't like to assume too much from one photo of from one angle, and I had previously been annoyed by some very poor analysis a long time ago that suggested the partly circular object on the left was part of one of the reactor well concrete top plugs (scale is totally wrong for that), so I was probably too negative about your later analysis.

I know I went on a few times about the possibility that the fuel handling bridge could have been blown out of the building in a way that made it tip over the southern edge of the building to the ground below, but I was not especially wedded to this theory in particular. We have come quite a long way from the days where people were studying the first high res photos for signs of the resting place of the refuelling bridge, partially due to expectations that the bridge might have been blown vertically high into the air, since the dramatic explosion footage of reactor 3 captured got a lot of attention. I don't think there was anything wrong with people at least briefly considering the more dramatic pool possibilities such as prompt criticality, but there was never any hard evidence that should have strongly pointed people in that direction. Anyway like I said its been quite a long time since those early confusing days and the theories that followed evolved into something that's quite a bit less dramatic. In other places on the net I sometimes fight against some very silly hype and fear mongering because I don't really know why some people feel the need to hype Fukushima or convince themselves that something more dramatic took place than actually seems to be the case, since the Fukushima disaster is quite bad enough already, quite enough contamination and long-term problems already without needing to cling to the least likely theories.

I feel like I should start to spend less time thinking & talking about Fukushima now, simply because the amount of new information and understanding does not match our appetites, and I fond myself sometimes still going on about stuff in detail that is probably not so important.

 

[SteveElbows]

The steam seems to be coming from around the well-cap rim, as was usual after the blast. One well-cap steam-ejection spots was right at the north edge of the pool.

This is my best effort to superimpose the floor plan onto the 3-minute-after image.

The satellite images seem to skew square buildings somewhat, so the floor plan is slightly skewed I hope to the best fit. I believe the steam is not coming from the pool but from around the primary containment, as seen in a lot of imagery from the early days.

Yes, that matches what I think I've seen in such images and certain videos.

This is one of many reasons that I find it try hard to form solid conclusions about just how bad a state reactor 3 pool got into later on. lack of clear visual evidence of pool emissions. A range of possibilities still seem to exist, and looking at how much rubble they probably have to deal with in the pool means it may be quite a long time before we get good confirmation of the exact state of all the fuel in that pool. I tend to assume that all things considered the pool & fuel didn't do too badly, but this is not a totally safe bet to make just yet.

 

[SpunkyMonkey]

This didn't mean I ruled out the possibility that the refuelling thing was in the pool

Understood, no problem! If it turns out the be the right interpretation as the trolley, admittedly it's a very 'abstract' interpretation given the mangled state of all the objects and that not one of them is a 100% obvious match. But perhaps one perfect match is the color of the fallen-in objects, which seems to me to be almost exactly the same olive-green as the refueling crane.

 

[jim hardy]

This is my best effort to superimpose the floor plan onto the 3-minute-after image.

nicely done ! Helicopter video looks like a narrow plume too.

 

[tsutsuji]

I'd still like to know what the theory behind this trend is.

http://sankei.jp.msn.com/affairs/news/120413/dst12041311480002-n1.htm unit 1's RPV [This what is written. I guess they mean PCV] temperature being measured close to the nitrogen injection line, it rose by 5°C as the [nitrogen] supply was shut down.

http://www.shimbun.denki.or.jp/news/main/20120413_04.html Because of that, the temperature of the PCV near the location where nitrogen is injected slightly rose, but there was no major variation of the internal hydrogen concentration.

http://www.asahi.com/national/update/0413/TKY201204130428.html Tepco says the cause for the nitrogen injection shut-downs on 12 March and on 4 April is thought to have been air inlet filters being clogged.

 

[SpunkyMonkey]

120413_04.jpg

Here's one of Tepco's photos of a SFP3 fuel rack:

And here I've enhanced its contrast, brightness and color and added a noise-reduction filter:

Brings out more detail. Looks like a deep 'snow' of fine-grain debris covers the top of the rack. If you get both images above in consecutive pages in one browser tab, you can toggle back and forth to appreciate how the enhanced image is like throwing a spotlight into the murky scene.

 

[SteveElbows]

Thanks as always for the helpful information about the nitrogen & reactor 1 temperature.

 

[SpunkyMonkey]

nicely done ! Helicopter video looks like a narrow plume too.

Thanks Jim! :)

I know I went on a few times about the possibility that the fuel handling bridge could have been blown out of the building in a way that made it tip over the southern edge of the building to the ground below, but I was not especially wedded to this theory in particular. We have come quite a long way from the days where people were studying the first high res photos for signs of the resting place of the refuelling bridge, partially due to expectations that the bridge might have been blown vertically high into the air, since the dramatic explosion footage of reactor 3 captured got a lot of attention. I don't think there was anything wrong with people at least briefly considering the more dramatic pool possibilities such as prompt criticality, but there was never any hard evidence that should have strongly pointed people in that direction. Anyway like I said its been quite a long time since those early confusing days and the theories that followed evolved into something that's quite a bit less dramatic.

Nice retrospective. Fukushima really challenged our sense of limits and what to expect as one after another reactor building exploded. Probably almost nobody expected that much, and it left everyone with a healthy sense of omg, what next. I have to remind myself of that when I see people hyping baloney like impending China-syndrome-triggered hydrovolcanic explosions. Fukushima established some background data for inductive inferences to events exceeding imagination.

But to a large degree, careful examination has tended to scale down some early expectations. But a question the crane falling in the pool raises is: Could a hydrogen-only explosion in the upper-deck space dislodge a 35-ton machine and shove it into the pool?

 

[Most Curious]

Thanks Jim! :)




But a question the crane falling in the pool raises is: Could a hydrogen-only explosion in the upper-deck space dislodge a 35-ton machine and shove it into the pool?

Hydrogen launched the Saturn 5.

Enough hydrogen, well mixed with exactly the right amount of air could release a LOT of energy!


Looking at the crud on top of the fuel assemblies in #3 makes me wonder something. If convective cooling of the fuel stops due to blocking the water flow with debris would the fuel cladding be overheated enough to bulge, crack and fail?

 

[MadderDoc]

<..>a question the crane falling in the pool raises is: Could a hydrogen-only explosion in the upper-deck space dislodge a 35-ton machine and shove it into the pool?

The machine may well have been not overly displaced by the immediate effect of the explosion, but then came down the roof on top of it.

 

[jim hardy]

But a question the crane falling in the pool raises is: Could a hydrogen-only explosion in the upper-deck space dislodge a 35-ton machine and shove it into the pool?

i guess we don't know when it fell into pool. Could it have got tossed about by earthquake?
If it's like my PWR crane it's not much of a shove. It straddles the pool and has steel wheels that run on steel rails just a few inches from edge..


More likely to me - Given the destruction to the building from the explosion it's conceivable a supporting wall moved far enough to be no longer underneath the crane's wheels.

Still waiting to see what's under that rubble on top floor.

old jim

 

[SpunkyMonkey]

Hydrogen launched the Saturn 5.

Though there's a huge difference between the directionally focused thrust of a rocket and an open-air gas explosion.

Looking at the crud on top of the fuel assemblies in #3 makes me wonder something. If convective cooling of the fuel stops due to blocking the water flow with debris would the fuel cladding be overheated enough to bulge, crack and fail?

Good question! And being covered like that for years.

The machine may well have been not overly displaced by the immediate effect of the explosion, but then came down the roof on top of it.

True. And which fits with the ladder's hand railing apparently being entangled with a roof girder, which might seem to imply that the crane was upright when it got hit with roof parts, and then the entanglement held the ladder close to its original position as the crane was torn away from it, falling into the pool. The ladder also provides an indication of the likely initial position of the crane, which would seem to be biased to the North side.

I think only or mostly the girders and some steel roof-decking came down, whereas bitumen was blown upwards and constituted the bulk or all of the large debris falling out of the mushroom cloud. In the same video we can see the bitumen of Unit 1 get blown up like a giant black rug, then fall back down. Consistent with that interpretation, we saw the bitumen of Unit 1 (looking like a giant moth-eaten rug) draped across and covering the remains of its upper deck. But for Unit 3, there was no sign of its bitumen afterward, except in my estimation as residual holes smashed through nearby roofs.

 

[SpunkyMonkey]

i guess we don't know when it fell into pool. Could it have got tossed about by earthquake?

I think the best working explanation is MadderDoc's idea that the refueling crane was hit by falling roof material. The entanglement of the hand railing on the crane's ladder with a roof girder would seem to support that scenario. It seems to imply that the crane was still in its normal position when the girder became entangled with the hand railing. And the hand railing should have fallen in (given that it was not anchored to anything but the crane) had it not become girder entangled, thereby holding it in place over the pool's edge as the crane plunged into the pool.

What I wonder is why we don't see any sign of the pool-spanning length of the crane's tracks in the open area of the pool. I guess it's down too deep. Or was it rotated to the side? My interpretation of the http://www.tepco.co.jp/en/news/110311/images/110415_1f_4_2.jpg (and) suggests the crane is still roughly in its original north-south alignment, and thus the trolley tracks should span the pool east to west.

 

[Joffan]

Both Unit 3 and Unit 4 spent fuel pool pictures suggest to me that Tepco should rapidly pursue an active pool water filtration system - does anyone know if that is in the plan?

 

[HowlerMonkey]

Hydrogen launched the Saturn 5.

Saturn V was launched using kerosene fuel.

It was flown out with two other stages that were fueled by hydrogen but it was launched using kerosene.

 

[Cire]

Hydrogen launched the Saturn 5.

Enough hydrogen, well mixed with exactly the right amount of air could release a LOT of energy!

Just to be correct. RP-1 (refined kerosene) launched the Saturn V. Only the upper stages are (J2 engines) Hydrogen powered.

 

[jim hardy]

Your "AND" video has a nice pause at 50 seconds.

I would guess there should be a crane rail along that crumbled wall on right hand side for the crane to run on.
If the top of that wall and its rail moved out from under that side of crane it'd tumble right in with its end pulled away from wall as it appears to be.

EDIT judging by what looks like rebar sticking into pool a substantial amount of concrete went someplace.

just a possibility. Clearer and more detailed photos will tell, in time.

old jim

 

[MadderDoc]

Both Unit 3 and Unit 4 spent fuel pool pictures suggest to me that Tepco should rapidly pursue an active pool water filtration system - does anyone know if that is in the plan?

I don't know what the status of those systems are currently. By about November last year, a mobile reverse osmosis filtration system had been used since August, to bring down the concentration of chloride in the pool of unit 4 from about 2000 ppm to about 150 ppm, and it was planned to continue filtration from there, using a mobile ion exchanger system to reach a target of 10 ppm by the end of the year. Similar desalination of the other pools were planned to be implemented 'in turn'.

 

[Most Curious]

Just to be correct. RP-1 (refined kerosene) launched the Saturn V. Only the upper stages are (J2 engines) Hydrogen powered.

oops! You are correct and I stand corrected that the 1st stage was kerosene and the uppers hydrogen fueled. The shuttle used hydrogen main engines and solid fuel exernal boosters.

My point remains the same - hydrogen and appropriate amount of air can make a big bang! The claims made early on of a nuclear type explosion in the pools was, and remains, nonsense IMHO.

In order to put the crane into the pool would only require blowing the walls outward far enough for the trolley to fall off the rails, which may well have been what happened.

 

[Rive]

In order to put the crane into the pool would only require blowing the walls outward far enough for the trolley to fall off the rails, which may well have been what happened.

The FHM rails are embedded into the floor of the fifth level. What you wrote is OK for the overhead crane only. To push the FHM into the pool you need a different punch.

I could not check all the information: can somebody please make a small drawing about the expected position of the FHM? Which end of it is on the bottom and so.
Very thanks.

 

[westfield]

i guess we don't know when it fell into pool. Could it have got tossed about by earthquake?
If it's like my PWR crane it's not much of a shove. It straddles the pool and has steel wheels that run on steel rails just a few inches from edge..

<snip>

old jim

Personally, I think the quake could easily have been what sent the FHM into the pool but as you say we may never know unless eyewitnesses can tell us or site CCTV footage emerges at some time. But look at how top heavy most FHM's are.

Tepco itself had in the past considered FHM's falling into a SFP a risk big enough to spend money on seismic upgrades - that speaks volumes to me.

Following the large earthquake that damaged Tepco's Kashiwazaki-Kariwa NPP a "fuel handling machine seismic upgrade" was one of only six main seismic upgrades across all units there. For some reason (which I have not yet found in any reports so far) Tepco decided to spend a good deal of time and money to reduce the risk of the top part of the machine "derailing" during a seismic event (presumably to reduce the risk of it falling off its bridge into the pool). Tepco did report major SFP "sloshing" in all the SFP's during that earthquake which led to some SFP water finding its way into the ocean. In a nutshell the main modification was adding additional "stops" so to speak to prevent the top part, ie the machine proper, lifting off its rails that run across the bridge it sits on. I read a Tepco report on this last year which had an image of the actual modification performed but cannot for the life of me find the document on Tepco's site now :(


Image of Kashiwazaki-Kariwa SFP "sloshing" during 2006 earthquake. All the unit's operating floors were wet with SFP water after the quake there.

Edit : btw, having said all the above I still don't think we can be sure the FH machine itself is actually in the SFP even though we now know with certainty at least one end of it's bridge is in there, apparently near the cask area of the pool. Which corner of the U3 SFP is the cask loading area? NW like unit 4 or did I see it in the NE corner in a drawing somewhere?

Edit: I did find a report with images of a KK FHM but in Japanese - Page 30-32 of this PDF

 

[MadderDoc]

<..> a report with images of a KK FHM but in Japanese - Page 30-32 of this PDF

Thanks a lot.

I have attached a schematic of the FHM from that document, if someone knows the correct terminology for the different parts, I'd be happy to adopt it.

The arrows point to parts which could have been improved as indicated in the document in order to protect the crane waggons from unrailing.
From what we have seen of the corresponding parts in unit 2 and 3, they do not seem to have any such improved designs.

 

[SpunkyMonkey]

The FHM rails are embedded into the floor of the fifth level.

Right, so blowing out the walls isn't a prerequisite for knocking down the FHM. But the scenario that it was knocked into the pool by falling roof girders seems pretty clear given the entanglement of the FHM ladder with a roof girder, which, because the ladder was previously supported only by the FHM, seems to dictate that the FHM must have been in its normal position when the girder became ladder entangled.

FYI All, here's a westerly view of SFP3 on 03/16/11 from Tepco video 3. It's just 5 frames run forward, backward and looped. They're the only reasonably clear frames in a very-quick camera pass of the pool area. Along with the 03/16/11 easterly view of SFP3, this also indicates that the pool was full before water was added for there's a lot of roof 'girders' just under the water that can be seen in closer westerly views and that should be visible if the pool was even low. But since the girders underwater are not visible from the further out view, it follows that they're covered with water.

 

[westfield]

Right, so blowing out the walls isn't a prerequisite for knocking down the FHM. But the scenario that it was knocked into the pool by falling roof girders seems pretty clear given the entanglement of the FHM ladder with a roof girder, which, because the ladder was previously supported only by the FHM, seems to dictate that the FHM must have been in its normal position when the girder became ladder entangled.
<snip>.

That ladder IS strange to be just there but I don't think we can be so conclusive about how it remained there and how the FHM got where it is..

For instance it's not impossible that the ladder could have jammed itself in that position in the FHM floor track as the FHM went into the pool, only later to have the roof truss come down next to it, ladder has nowhere to go as its stuck in the track so it's handrail "clips" itself over the roof truss section.

Just another possibility of course. We cannot be conclusive without more information.

(Also, a correction to my previous post - I put "2006 earthquake" , should have been "2007 earthquake". )

 

[westfield]

Thanks a lot.

<snip>

From what we have seen of the corresponding parts in unit 2 and 3, they do not seem to have any such improved designs.

A note to all related to that - the FHM's across the 6 units at fukuichi are not even close to identical.
The most obvious differences are the type of bridge they have, Toshiba which seem to feature truss type bridges (like unit 3), some are Hitachi which seem mainly to have box section type bridges (like unit 4). There are also differences in each succesive design as well. I.e the Toshiba FHM's have design differences in each unit.

I've noticed bridge design , umbilical design\layout, control console shape and layout of equipment right at the top of the FHM are easy ways to distinguish the different FHM's.

Many people would also have noticed this but be aware that around the net there are many many images of FHM's & operating floors identified as fukuichi but they are clearly not from the units or even the country they supposedly are.

 

[MadderDoc]

<..>
My point remains the same - hydrogen and appropriate amount of air can make a big bang! The claims made early on of a nuclear type explosion in the pools was, and remains, nonsense IMHO. <..>

Yes, no argument there, but can hydrogen and the appropriate amount of air produce that big cloud, such as we saw in the case of unit 3?

A volume of about 30000 m3 of explosive mixture could have been contained in the upper floors of the building (40x40x20 meters), certainly capable of producing a big bang, as well as lot of destruction, and flying debris and dust clouds, as we all saw in the video.

But on top of that, moments after the explosion we have this big cloud rising over the building, apparently approximately spherical, 75 m diameter -- which would be a volume of about 220000 m3. So where did this huge volume of air come from, how did it get there, what was its composition??. This is where 'hydrogen explosion' seems to me to be seriously lacking in explanatory power: it appears to have that cloud coming out of nowhere. Like some Crocodile Dundee. Like magic. Black magic :-)

 

[MadderDoc]

A note to all related to that - the FHM's across the 6 units at fukuichi are not even close to identical.

Though, if I may moderate your expression, the FHM's of unit 2, unit 3, and the common pool, all do appear to be very similar.

 

[elektrownik]

Unit 3 SFP Video: http://photo.tepco.co.jp/en/date/2012/201204-e/120416-02e.html
Project of construction for removing fuel from SFP Unit 4: http://photo.tepco.co.jp/date/2012/201204-j/120416_03j.html

 

[Rive]

But on top of that, moments after the explosion we have this big cloud rising over the building, apparently approximately spherical, 75 m diameter -- which would be a volume of about 220000 m3. So where did this huge volume of air come from, how did it get there, what was its composition??

As the steam plumes on the right-after-the-explosion picture suggests the containment integrity was broken at that time. As I recall after the explosion the RPV remained on ambient pressure.

So my bet:
The PCV released pressure and the hydrogen stocked up in the secondary containment till it exploded: this was the first 'bang'.

Then the RPV damaged and the overheated water in it turned to steam. This steam (and some more hydrogen) built the big cloud. Fortunately the wind moved the cloud toward the ocean, so the site remained relatively safe: also the steam separator stopped the worst of the solid fuel debris.

 

[SteveElbows]

For general reference, here are a couple of images and a couple of videos that represent the most recent views of the reactor buildings that I have been able to find so far:

These photos are from March 11th 2012 I believe:

http://msnbcmedia.msn.com/j/reuters/2012-04-03t131611z_1_cbre83210v200_rtroptp_3_japan-tsunami.grid-6x3.jpg

http://msnbcmedia.msn.com/i/reuters/2012-03-30t130143z_1_cbre82t106y00_rtroptp_3_japan-tsunami.jpg

This video is from late Feb when they reduced the flight exclusion radius:



This video has a few seconds that appear more recent, starting from the 33 second mark of this youtube clip:



I note that the met viable signs of progress at reactor 3 are the removal of damaged building at ground level to the north of the reactor, and the construction of a structure near the north-east of the reactor building.

 

[SpunkyMonkey]

That ladder IS strange to be just there but I don't think we can be so conclusive about how it remained there and how the FHM got where it is..

For instance it's not impossible that the ladder could have jammed itself in that position in the FHM floor track as the FHM went into the pool, only later to have the roof truss come down next to it, ladder has nowhere to go as its stuck in the track so it's handrail "clips" itself over the roof truss section.

Not a bad idea, though I don't get how or why the hand rail 'clips' itself over the truss. Seems like that 'clip over' effect might be best explained by a downward pull as the FHM falls into the pool, briefly deforming the rail downward (clip down) before the relatively weak rail snapped.

In any scenario how that truss gets in there is really bizarre. If it did so before the FHM fell, was it thrust at an almost horizontal angle like a javelin? That seems very unlikely. I'm also not sure based on the before photo if there was enough room for it to slide under the rail. Very strange indeed!

 

[SteveElbows]

Unit 3 SFP Video: http://photo.tepco.co.jp/en/date/2012/201204-e/120416-02e.html

Cheers.

On first viewing, videos 3 & 5 offer us some views that were not apparent from the previously released photos.

Has anyone been able to identify any of the debris we see in the 5th video?

 

[clancy688]

As the steam plumes on the right-after-the-explosion picture suggests the containment integrity was broken at that time. As I recall after the explosion the RPV remained on ambient pressure.

So my bet:
The PCV released pressure and the hydrogen stocked up in the secondary containment till it exploded: this was the first 'bang'.

Then the RPV damaged and the overheated water in it turned to steam. This steam (and some more hydrogen) built the big cloud. Fortunately the wind moved the cloud toward the ocean, so the site remained relatively safe: also the steam separator stopped the worst of the solid fuel debris.

That isn't consistent with pressure data (March 14th):

Time                    RP(A)   RP(B/C) D/W       S/C      FNT    BHT     WL(A)  WL(B)   DW R/H         Ref
                        MPa abs MPa abs MPa abs   MPa abs  gr.C   gr.C    meter  meter   gr.C

23:00, March 14th       N/A     0.297   0.370     dscale    N/A    N/A     N/A   -2.30
22:40, March 14th       N/A     0.290   0.360     dscale    N/A    N/A     N/A   -2.30
22:00, March 14th       --approximate time for a fire at unit 3 or 4 -----------------
21:04, March 14th       N/A     0.270   0.360     dscale    N/A    N/A     N/A   -2.30
20:03, March 14th       N/A     0.284   0.360     dscale    N/A    N/A     N/A   -2.30
19:30, March 14th       N/A     0.283   0.335     0.500     N/A    N/A    -1.90  -2.30
19:00, March 14th       N/A     0.284   0.360     dscale    N/A    N/A     N/A   -2.30
17:00, March 14th       N/A     0.362   0.440     0.440     N/A    N/A     N/A   -2.20
16:00. March 14th       - webcam shows smoke coming from unit 3-----------------------
16:00, March 14th       N/A     0.409   0.480     0.475     N/A    N/A     N/A   -2.20
15:00, March 14th       N/A     0.399   0.480     0.470     N/A    N/A     N/A   -2.20
14:00, March 14th       N/A     0.382   0.460     0.450     N/A    N/A     N/A   -2.20
13:00, March 14th       N/A     0.352   0.430     0.430     N/A    N/A     N/A   -2.20
12:00, March 14th       N/A     0.292   0.380     0.380     N/A    N/A     N/A   -2.20
11:30, March 14th       N/A     0.291   0.360     0.380     N/A    N/A     N/A   -1.80
11:25, March 14th       N/A     0.292   0.360     0.380     N/A    N/A     N/A   -1.80
11:15, March 14th       N/A     0.316   0.380     0.390     N/A    N/A     N/A   -1.60
11:01, March 14th       ----------------- explosion in reactor building---------------
09:05, March 14th       N/A     N/A     0.450     N/A       N/A    N/A     N/A    N/A
09:00, March 14th       N/A     0.409   0.490     0.475     N/A    N/A     N/A   -1.50
08:00, March 14th       N/A     0.421   0.500     0.490     N/A    N/A     N/A   -1.00
06:50, March 14th       N/A     N/A     0.650     N/A       N/A    N/A     N/A    N/A
07:00, March 14th       N/A     0.439   0.520     0.500     N/A    N/A     N/A   -3.00
06:00, March 14th       N/A     0.282   0.425     0.400     N/A    N/A     N/A   dscale
05:00, March 14th       N/A     0.282   0.365     0.345     N/A    N/A     N/A   dscale
04:00, March 14th       N/A     0.260   0.340     0.325     N/A    N/A     N/A   -2.80
03:00, March 14th       N/A     0.235   0.315     0.305     N/A    N/A     N/A   -2.30
02:00, March 14th       N/A     0.178   0.275     0.275     N/A    N/A     N/A   -2.25
00:30, March 14th       N/A     0.152   0.255     0.255     N/A    N/A     N/A   -2.2

Containment pressure did fall after the explosion, but it rose again to higher levels. Not the behaviour I'd expect from a leaking containment. But there's also the possibility that the sensor, as so many others, already went to hell at that point.

Taken from:

http://gyldengrisgaard.dk/fukmon/uni3_monitor.html

 

[SpunkyMonkey]

Has anyone been able to identify any of the debris we see in the 5th video?

We seem to see main horizontal beams of the FHM that ran east-west across the pool. If we refer to the same video.

 

[SpunkyMonkey]

Containment pressure did fall after the explosion, but it rose again to higher levels. Not the behaviour I'd expect from a leaking containment.

But that the containment was leaking after the explosion is obvious, for example "www.youtube.com/watch?v=iV_r5Ifp8-I&hd=1#t=44s" . What one has to consider is that probably after the blast, melting fuel kept off gassing and more corium kept forming, boiling water ever-more vigorously and thereby increasing the pressure.

The containment was not blown wide open, just enough small leak paths were blasted open to have allowed a mushroom-cloud of steam to escape in an instant of sudden explosive force. After the explosion, the force propelling depressurization falls and pressures build back up as corium keeps off gassing and boiling water.

 

[Rive]

That isn't consistent with pressure data (March 14th):

Indeed. Very thanks for the data. Then the explosion-like sudden decompression can be excluded.

However I think it's safe to assume that something had a leak there after/around the time of the explosion: the data shows steady downward trend without venting attempts.

Then maybe some more hydrogen stocked in the lower parts of the building can be an explanation?

... small leak paths...

I think small leak paths would not be enough for that big mushroom cloud. An overheated RPV would, but small leaks wouldn't.