Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[shogun338]

T- Hawk video from 4-15-11 shows a closeup of the gray mass in Unit 4 around 2.48 and it appears to be rubber roof sheathing or something similar .

 

[shogun338]

RADIATION levels around Japan’s stricken nuclear plant soared after another earthquake jolted the *country yesterday.

Read more: http://www.mirror.co.uk/news/top-st...her-earthquake-115875-23066249/#ixzz1JkYl16i3

 

[MadderDoc]

New T-Hawk video from 4-15-11 . Some closer shots of Unit 1 and Unit 3 . Video quality looks a little better .

Yes, and thank you so much for making those HQ videos available.

About unit 3, perhaps Tepco should now come out with a some straight words about what exactly has happened to it. By now they must have a pretty clear picture.

 

[Joe Neubarth]

RADIATION levels around Japan’s stricken nuclear plant soared after another earthquake jolted the *country yesterday.

Read more: http://www.mirror.co.uk/news/top-st...her-earthquake-115875-23066249/#ixzz1JkYl16i3

Well Shogun, just like we do not have the actual explanation as to why the Earth's molten core causes our magnetic field that helps shield the Earth from solar/cosmic radiation, do we absolutely know what is happening in those reactors when the Earth shakes and the radiation levels soar.

Are we seeing limited Earth shaken fission; or, do the gamma rays wait for a good shake before being born?

 

[shogun338]

All videos of Unit 3 have shown steam or smoke at times escaping from reactor location . This shows that outer containment of RPV has been breached at least . I think this had a lot to do with the huge explosion we all seen at Unit 3 . Unit 3 is also the one loaded with the MOX fuel . This may have something to do with what is seen at Unit 3. NO one wants MOX fuel . ---The U.S. Department of Energy wants to redesign its partially built mixed oxide fuel plant to make nuclear fuel for a wider variety of reactors.
The facility under construction at Savannah River Site is designed to make fuel rods for pressurized water reactors in use at many commercial power plants. http://chronicle.augusta.com/news/metro/2011-04-15/officials-review-plan-changes-mox-facility

 

[shogun338]

Well Shogun, just like we do not have the actual explanation as to why the Earth's molten core causes our magnetic field that helps shield the Earth from solar/cosmic radiation, do we absolutely know what is happening in those reactors when the Earth shakes and the radiation levels soar.

Are we seeing limited Earth shaken fission; or, do the gamma rays wait for a good shake before being born?

I think there just worried it has caused a new leak .-- But the government said Saturday that levels of radioactive materials in the seawater have risen again in recent days. The level of radioactive iodine 131 jumped to 6,500 times the legal limit, according to samples taken Friday, up from 1,100 times the limit in samples taken the day before. Levels of cesium 134 and cesium 137 rose nearly fourfold. The increased levels are still far below those recorded earlier this month before the initial leak was plugged.

The government said the new rise in radioactivity could have been caused by the installation on Friday of steel panels intended to contain radioactive materials. The construction may have temporarily stirred up stagnant waste in the area, Hidehiko Nishiyama, the deputy director general of Japan’s nuclear regulator, the Nuclear and Industrial Safety Agency, told reporters. However, the increase in iodine 131, which has an eight-day half life, could signal the possibility of a new leak, he said. http://www.nytimes.com/2011/04/17/world/asia/17nuke.html?src=mv

 

[I_P]

Kyodo is reporting that two robotic units with temp, radiation, and 02 sensors (and cameras?) will enter unit 3 today to see if it is safe for workers to enter and begin stabilization measures. If successful they will try the same in units 1 and 2.

 

[HowlerMonkey]

OK, then a stoichiometric or oxygen-rich acetylene fire will release an absolutely IMMENSE white flash, I mean almost nuclear detonation-class flash that would be seen for miles.

But, an acetylene cylinder that is punctured will not generally release acetylene very quickly, it takes a while to fizz out of the acetone/filler mix. The tanks are filled with a clay-like filler, and then saturated with acetone, then the acetylene is dissolved in that sort of like CO2 in soda.

Jon

I'm still not sure any of that happened.

I just tried to explain a theory put forth earlier in the thread though an acetlyene cylinder can be persuaded to release all of it's fuel by an explosion of a much thicker higher pressurized oxygen cylinder exploding beside it...since they are usually chained together.

After being involved with lexus and seeing the factory, I believe that the average skilled laborer in japan is unbelievably responsible and many mistakes put foward are mostly impossible except for the possibility that they could have been "caught out" by the tsunami event and unable to secure everything properly.

If any mistakes are being made, it is with management and not the guys doing the actual work.

 

[|Fred]

Thank you for the link to the video , I should have looked at tepco's..
too bad the most interesting bit it not there..
still we learn a few interesting points:

-blast on unit 4 does not seems to originate side ways on a low level of the SFP as we can see the concrete wall of the pool on the est wall are pristine while wall are blasted. (that's an other confirmation of what we assume)

- there is an other canal opening linking operating floor to bellow on the south east more or less rectangular 1/2 the with of the assumed cast canal.

- there is an other green fuel small handling crane above the utility pool (this confirm the hypothetical assessment I made 17 days ago (click link bellow to see the picture)

caption contest :(
Crane Crane, reactor open lid ?What's the crane on the right (north) doing there ?

This may also contribute to infirm the Ballistic FHM

 

[cphoenix]

I had written: "If a pool were in that condition, and then were shaken, the water might flash into steam very quickly. At 2260 J/g, 5E11 J could vaporize about 200 Mg (tons) of water. At ~600 g/m^3 density for steam at 1 bar, that would be about 300,000 cubic meters, or a 70-meter cube.

but where is the triggering quake?
http://neic.usgs.gov/cgi-bin/epic/e...AT=0.0&CLON=0.0&CRAD=0.0&SUBMIT=Submit+Search

I shouldn't have said "shaken." I should have said "disturbed." It would not require an earthquake. At some point, with continuous heating, the water would get hot enough to bubble under 2 atm of pressure, and then the pool would disturb itself. (Not very hot - ~125 C.)

Significant bubble formation would cause a reduction in pressure, which would allow more water to flash to steam, creating more bubbles... the process would run away, just like those CO2-loaded lakes that occasionally invert their water layers and emit massive amounts of CO2. But with many pounds of TNT-equivalent per cubic meter of superheated water, the process could be quite violent.

In a follow-on post, I had suggested that convection could be reduced enough to create this effect by an earthquake knocking a flat piece of material into the pool so that it covered the top of a fueling rack. This would not trigger the explosion; it would create the conditions for the heating to start. Sometime later, the explosion would trigger itself.

 

[TCups]

@AtomicWombat

Help me with this. If the FHM3 (or at least part of it) is still in SFP3, then what is(are) the large green object(s) that look as if they fell from the sky and smacked the northwest corner of building 3? Maybe the FHM did break up.

http://i306.photobucket.com/albums/nn270/tcups/Picture7.png

http://i306.photobucket.com/albums/nn270/tcups/Picture6-1.png And what might this large, curved, slab-like object that looks as if it hit an inner wall of Bldg 3 be? A "cookie"? Could the primary containment, once it "blew" not only have blown out the fuel transfer chute, but also, blown out some of the semi-circular portions of the "neck of the primary containment below the level of the service floor, and therefor, been the driving force in the blow out of the lower portions of Bldg 3 as well? We still have 3 booms to explain.

http://i306.photobucket.com/albums/nn270/tcups/Picture8-2.png

More and more questions.

 

[shogun338]

Any TVA move on the proposal has been put off pending a review of the behavior of MOX fuel at Japan's Fukushima Daiichi nuclear power plant, which was severely damaged last month by a 9.0-magnitude earthquake and tsunami . The federal investigation would address the extent to which the MOX fuel -- which comprised 6 percent of the material in the Japanese facility's No. 3 reactor -- has heated and broken down since the March disasters.
“We are studying the ongoing events in Japan very closely,” TVA spokesman Ray Golden said.
The Mixed-Oxide Fuel Fabrication Facility, a site under construction at the Savannah River Site in South Carolina, would convert 34 metric tons of excess weapons plutonium to nuclear power plant fuel, according to an earlier report. The facility's expense has reached almost $5 billion since the government signed a contract for its creation, and no entity has officially stepped forward to buy the fuel. http://www.globalsecuritynewswire.org/gsn/nw_20110411_6298.php

 

[shogun338]

Unit 4--Workers were firing water into the pond from a distance in an effort to prevent the fuel from overheating and releasing radioactive contaminants, but fluid collecting in an adjacent flood control container triggered an incorrect warning that the pond had been filled. Personnel halted water transfers to the pool for a number of days in response to the warning, allowing heat and radiation levels to increase even though the fuel was thought to have remained submerged, Japanese Nuclear and Industrial Safety Agency Deputy Director General Hidehiko Nishiyama said. Water spraying began again on Wednesday. http://www.globalsecuritynewswire.org/gsn/nw_20110414_5466.php

 

[cphoenix]

The more I look at the damage to 4 in the high-quality videos, the more I'm struck by how gentle (slow) the explosion must have been. Certainly very forceful, to have crumbled concrete. But it looks more like something pushed the panels out, than like something blasted the panels out. And that gray stuff lying near the crane - it seems almost draped over the debris, as though it had not fallen very far or very violently. A lot of stuff seems tumbled around, not blasted up and dropped from hundreds of feet (like unit 3).

This, plus the lack of soot, makes me like the superheated-water hypothesis more. The explosion would not generate over 2.25 atm (absolute) of pressure... but there would be a massive amount of gas generated.

I don't know the hydrodynamics, and it would depend on what parts of the building failed at what time. But I can imagine a boiling mist of water erupting from the pool, pressurizing the building, spraying off of surfaces, perhaps finding its way below-decks before it finished boiling.

Any guesses as to how much pressure differential it would take to blow out those panels? They weren't designed for sideways load, and many tons of force could be applied with just a little superheated water in a confined space.

This might also explain how pool 4 can still hold water, after something crumbled out a concrete wall next to the pool (if I understand the pictures correctly). Most of the pressure release would be upward from the pool, following the path of least resistance left by the boiling. But there'd be an overpressure above the pool - again, fairly gentle, but perhaps on the order of an extra atm of pressure over a large area. And there'd be lots of sloshing in the pool, and maybe water-hammer effects. A diffuse, slowly-applied force might crumble concrete without ripping steel.

Chris

 

[|Fred]

Help me with this. If the FHM3 (or at least part of it) is still in SFP3, then what is(are) the large green object(s) that look as if they fell from the sky and smacked the northwest corner of building 3? Maybe the FHM did break up..

Part of the utility/dryer pool crane/machine

 

[Dmytry]

The more I look at the damage to 4 in the high-quality videos, the more I'm struck by how gentle (slow) the explosion must have been. Certainly very forceful, to have crumbled concrete. But it looks more like something pushed the panels out, than like something blasted the panels out. And that gray stuff lying near the crane - it seems almost draped over the debris, as though it had not fallen very far or very violently. A lot of stuff seems tumbled around, not blasted up and dropped from hundreds of feet (like unit 3).

This, plus the lack of soot, makes me like the superheated-water hypothesis more. The explosion would not generate over 2.25 atm (absolute) of pressure... but there would be a massive amount of gas generated.

I don't know the hydrodynamics, and it would depend on what parts of the building failed at what time. But I can imagine a boiling mist of water erupting from the pool, pressurizing the building, spraying off of surfaces, perhaps finding its way below-decks before it finished boiling.

Any guesses as to how much pressure differential it would take to blow out those panels? They weren't designed for sideways load, and many tons of force could be applied with just a little superheated water in a confined space.

This might also explain how pool 4 can still hold water, after something crumbled out a concrete wall next to the pool (if I understand the pictures correctly). Most of the pressure release would be upward from the pool, following the path of least resistance left by the boiling. But there'd be an overpressure above the pool - again, fairly gentle, but perhaps on the order of an extra atm of pressure over a large area. And there'd be lots of sloshing in the pool, and maybe water-hammer effects. A diffuse, slowly-applied force might crumble concrete without ripping steel.

Chris

theres a problem with that. Slow-release overpressure blows out one or two panels and that's it. This should've crushed through floors to get to bottom. Furthermore, its precisely the slow applied force that would damage steel more for same amount of concrete crushing. It's the slow blast that tears non fragile stuff apart; its the fast blast that crushes fragile stuff without it flying far.
What if it had repeating transient criticality, water hammer style, shaking the building real bad? It seems plausible for me that there could be oscillations in the criticality, and the pool would be shaken very hard (by reaction of water).

 

[TCups]

RE: BLOW-OUT OF FLOORS BELOW THE SERVICE LEVEL ACCESS (TOP) FLOOR OF BLDG 3 - PROPOSED MECHANISM


(Is the circle still unbroken, by and by, Lord, by and by?)

1) Explosion occurs inside primary containment
2) Explosion lifts primary containment plug but does not blow it through the roof. Instead, the expanding gas blows out around the periphery of the plug, and through the fuel transfer chute in a radial, not vertical fashion
3) Lifting of the containment plug significantly compromises the structural integrity of the top rings of the primary containment in the "neck" region, surrounding the drywell cap, because
4) The top rings are discontinuous -- that is, they are segmented with sections to allow for removal of the fuel transfer chute gate to allow underwater access to the SFP (south side), and, removal of larger sections for underwater access to the equipment pool (north side). This leaves two larger, roughly semi-circular, segments of the top rings of the primary containment on the east and west sides, and, because
5) The "rings" of the neck portion of the primary containment are "tongue-in-groove" construction (see cross section diagram).
6) The radial force of the explosion in the primary containment can much more easily blow out the transfer gates and the semi-circular rings of the upper primary containment once the plug is lifted, than the vertical force of the explosion can lift the entire drywell containment plug large distances into the air.
7) The blow out of even one segment of one of the top rings might sufficiently decompress the initial drywell explosion to let the plug fall back down, albeit perhaps slightly askew, and certainly not well sealed
8) The blow out of any portion of the top ring of the drywell containment other than the transfer gate(s) vents the primary containment explosion into the lower building, not the upper building!

http://i306.photobucket.com/albums/nn270/tcups/Picture2-5.png

http://i306.photobucket.com/albums/nn270/tcups/Picture8-2.png

http://i306.photobucket.com/albums/nn270/tcups/Picture11-1.png

PS: shogun338 -- thanks for the link to the high res video. Lots more information there to ponder!

 

[dinorobo]

Tepco said today it will take them 6-9 months to cool down the reactors

http://english.kyodonews.jp/news/2011/04/86010.html

 

[TCups]

Part of the utility/dryer pool crane/machine

If so, how did it get lifted high enough in the air to come back down and do that kind of damage? If the mechanism of a steam explosion in the SFP3 is correct (I think so) and if the utility crane in Bldg 3 is "amidships" and the center section of the roof super structure is intact, as the photos show, and if only something over the SFP3 gets lifted vertically with enough oomph to go ballistic . . .

Could it be that either part of the FHM3 is still in the pool, or could it be that water added to the SFP3 causes the green color of whatever it is in the pool, or some combination of both?

Still more questions to be answered.

 

[AtomicWombat]

@AtomicWombat

Help me with this. If the FHM3 (or at least part of it) is still in SFP3, then what is(are) the large green object(s) that look as if they fell from the sky and smacked the northwest corner of building 3? Maybe the FHM did break up.

http://i306.photobucket.com/albums/nn270/tcups/Picture7.png

http://i306.photobucket.com/albums/nn270/tcups/Picture6-1.png

Part of the utility/dryer pool crane/machine

I've been wondering if there is a separate crane/machine over the equipment pool in each building.

And what might this large, curved, slab-like object that looks as if it hit an inner wall of Bldg 3 be? A "cookie"? Could the primary containment, once it "blew" not only have blown out the fuel transfer chute, but also, blown out some of the semi-circular portions of the "neck of the primary containment below the level of the service floor, and therefor, been the driving force in the blow out of the lower portions of Bldg 3 as well? We still have 3 booms to explain.

http://i306.photobucket.com/albums/nn270/tcups/Picture8-2.png

It looks like a piece of bent sheet metal to me.

I'm wary of drawing anything but tentative conclusions from image analysis, especially since we have no experience of working in these or similar plants.

It reminds me a little of seeing images of the aftermath of a bad car crash on TV. Often you can't work out the make and model of the cars involved let alone determine the details of what happened. On the other hand if you could sift through the debris personally you would probably be better able to form firm conclusions.

 

[AtomicWombat]

Can anyone unzip the topmost 3 videos here:
http://www.tepco.co.jp/en/news/110311/index-e.html"

I get an unrecognised format with WinRAR.

 

[TCups]

I've been wondering if there is a separate crane/machine over the equipment pool in each building.
It looks like a piece of bent sheet metal to me.

I'm wary of drawing anything but tentative conclusions from image analysis, especially since we have no experience of working in these or similar plants.

It reminds me a little of seeing images of the aftermath of a bad car crash on TV. Often you can't work out the make and model of the cars involved let alone determine the details of what happened. On the other hand if you could sift through the debris personally you would probably be better able to form firm conclusions.

Look again, AW -- if it's sheet metal, it packed a helluva wallop where it look like it struck the inside wall. But yws, it could be something else -- maybe sheet metal. . .

 

[zapperzero]

I get an unrecognised format with WinRAR.

Works fine using the latest version of WinZip. The new .zip format is not backwards-compatible.

 

[TCups]

Can anyone unzip the topmost 3 videos here:
http://www.tepco.co.jp/en/news/110311/index-e.html"

I get an unrecognised format with WinRAR.

Mac Quicktime says "not a movie file", but VLC utility opens the as a movie in mpg format.

 

[|Fred]

I see more of a collapsed wall, by a lateral blast than a death from above damage, the last roof structure with wise has been bent toward north .
Tcup I'm not sure I understood you, In my opinion they are 3 cranes, 2 small for pool operations on big for slab, and shield handling.

nb: it's a MPEG2 Video
ps: I'm skeptical at the "rings" theory, as it does not have to be a ring from the outside does it ?

 

[Krikkosnack]

Yep. I'm very surprised though that there was no word from explosion experts about the video. No estimates of energy, in traditional TNT equivalent.
I'm still looking for chimney height as quoted from official source. It seems clear to me that the explosion in #3 could not possibly have been a hydrogen explosion but I would love to have data to conclusively show it in the way that can't be easily denied.
I'm going to also base height on photo for now and figure out the air movements for the observed plume velocity (not the debris). I did some numerical fluid simulations in the past, this is going to take a while. But overall - this stuff is rising very very fast, I'm sure it is steam vented out of reactor, not steam from hydrogen combustion.

is exactly what I think ..

 

[NUCENG]

I have been reading a number of interesting reports from National labs including studies of Station Blackouts at Peach Bottom and Brown’s Ferry. Other reports cover failure modes of Mk 1 containments an others address the source term generation an transport from a severe accident. I found these documents by searching at the following link: http://www.scienceaccelerator.gov/

I have skimmed these documents looking specifically at time sequences, damage mechanisms and locations and hydrogen.

My latest conjecture seems reasonable from this reading. I may be completely wrong but I think it shows a possible way to account for differences between units.

Unit 1 is a BWR-3 and smallest of the units. It was the first to lose core cooling. They had no high pressure injection source and only the isolation condenser for core cooling, Operators (and management) were slow to reduce RPV and containment pressure because they didn’t want to lose the plant with low pressure injection of seawater. Operators would have used SRVs to keep pressure in the RPV below design limits, but this caused level to drop more quickly. As a result the core is probably 60 to 70 percent gone. When they finally used ADS to depressurize the reactor it created a huge source term and hydrogen gas concentration in the drywell and wetwell. Containment pressure was greater than 2 times its design rating. I believe containment failed at the drywell cap due to stretching of the hold down bolts and leaked into the refueling floor until pressure was relieved. The RPV was not significantly damaged. The hydrogen released on the refueling floor detonated blowing off the siding and lifting the roof. Overhead pictures of unit one don’t show much more than a featureless grey “floor” so much of the roof may have dropped right back onto the floor.


Units 2 and 3 are BWR-4s and used high pressure injection ECCS with RCIC and HPCI until the batteries were depleted. On Unit 2 operators used RCIC as long as they could. At Unit 3 they were unsuccessful in transferring from HPCI to RCIC so it was next to fail. Use of these high pressure sources maintained reactor level longer and explains the delay in their failures compared to Unit 1.

In Unit two I believe the containment failure occurred in the wetwell air space creating the loud noise near the torus reported by operators. The relatively smaller damage in Unit 2 was due to a relatively smaller core damage of perhaps 20 percent. There was enough of a detonation to pop the blowout panels on the refueling floor walls. Containment pressure dropped indicating the loss of containment. The RPV is probably intact.

Unit 3 had more damage to the core and released larger source terms and hydrogen amounts into the drywell and wetwell. I am guessing nearer to 50% ofr that core is gone. I believe the failure in the primary containment was at the vent lines or expansion bellows between the Drywell shell and the Torus. This provided a significant release of radioactivity and hydrogen low in the building which didn’t immediately detonate. There was some time for the hydrogen to diffuse and rise through the reactor building, turning the building into a huge grenade.

Eventually it detonated. Additional damage to the containment could have admitted air into the hydrogen rich drywell joining in for a bang seen as a rapid rising column of smoke and steam through the drywell reactor cavity. If the audio people have been playing with the multiple explosions could be due to the propagation of the detonation from floor to floor or into the drywell.

Unit 4 was shutdown, defueled and the reactor cavity was drained due to the core shroud replacement. There was some damage to fuel in the spent fuel pool, but not enough for a huge hydrogen explosion. It is possible that the pool was partially drained to the reactor cavity by damage to the gates. This neatly explains the thermal imaging showing heat in the pool and cavity. Since a large part of the pool water inventory was lost it would have reduced the time to start to uncover fuel in the pool. There were probably a few occurrences of zirconium fires in the pool which were apparently self-extinguishing. So whence cometh the damage to Unit #4 exterior? There appears to be photography showing Unit 4 intact after Unit #3 exploded. But look at Unit 3 in those pictures. There is concrete slab siding on the ground floor and two floors of open concrete support beams and girders. In the pictures showing Unit 4 damaged the seems to be another floor missing from Unit 3. The damage to Unit 4 is bent away from unit 3. Is it possible there was a second explosion at Unit 3 that caused the damage to Unit 4? The confusing reports of a possible explosion near unit 4 were during a period when there were few people on site and could actually have been from unit 3 which ahd significant containment damage but was probably still generating hydrogen.

Conclusions and consequences.

1. RPVs may be leaking, but remain intact and are still containing most damaged fuel. Evidence for this is a lack of evidence of core-concrete interaction.

2. Unit 1 containment is intact but leaking. Good thing or site doses would be much larger.

3. Unit 2 and Unit 3 have breached containments and adding water is washing more of the core into the environment. Inerting the containment may be impossible so feed and bleed is really the only choice they have.

4. Unit 4 fuel pool will have to be cleaned out and damaged fuell removed. Then this unit can be put into a storage condition.

5. Unit 1 may need repairs to containment to stop leakage but could be used to store its damaged core for a TMI-2- like cleanup.

6. Entombment may be the only option for units 2 and 3.

7. If core cooling is unsuccessful or RPV failures occur, this couuld still get a lot worse.

 

[Krikkosnack]

You can't calculate the mass from known trajectory. Every object having the same initial speed will behave identically (well, ignoring air resistance, but in the case of high density objects and not too high speeds that's quite good approximation).

this is true for the descent phase ... but for the rising phase?
Just because during descent objects behave in the same way (with Galileo), and neglecting air resistance in the first instance, the analysis of the descent phase of the object on the right, helps me to find out how they got there all those things at that height. In particular, I analyze the object on the right:

1) avoid perspective errors
2) to estimate precisely how much time is spent in the fall.
3) go up to the maximum height that has been pushed (for accuracy by comparing the height of the towers and buildings)
4) know the maximum height to which is the biggest body on the left (the top of the reactor?)
5) determine how much energy is in the game using http://en.wikipedia.org/wiki/Conservation_of_energy
6) try to do an analysis of the trajectories by analyzing the impact points to go back to the point of expulsion and analyze some holes on nearby buildings

All that I need to analyze explosions

 

[PietKuip]

In Unit two I believe the containment failure occurred in the wetwell air space creating the loud noise near the torus reported by operators. The relatively smaller damage in Unit 2 was due to a relatively smaller core damage of perhaps 20 percent. There was enough of a detonation to pop the blowout panels on the refueling floor walls. Containment pressure dropped indicating the loss of containment. The RPV is probably intact.

Thank you very much for this excellent informed overview!

So there are special blowout panels? Somewhere else I had read that the opening in the wall of Unit 2 had been made by workers in order to prevent hydrogen explosions, but it is unclear to me when this would have been done.

 

[elektrownik]

look on this, it is grat, table on page 5, they restore almost all sensors: http://www.meti.go.jp/press/2011/04/20110417002/20110417002-2.pdf

 

[NUCENG]

Thank you very much for this excellent informed overview!

So there are special blowout panels? Somewhere else I had read that the opening in the wall of Unit 2 had been made by workers in order to prevent hydrogen explosions, but it is unclear to me when this would have been done.

The blowout panels on the refuel floor are designe to trlieve at a few inches of water pressure as part of a function to protect the siding and roof from negative pressures during a tornado or during a steam line break in the reactor building. Fukusjma deliberately opened holes in unit 2 so they could spray water into the spent fuel pool. The blowout panels may not have been close enough to the pool.

 

[NUCENG]

No where near most. There are several thousand instruments in an operating BWR. In BWRs where I worked there were over 100 that were designated as "Post Accident Monitoring (NRC Regulatory Guide 1.97). There is a big list of measurements in that list that may not yet be restored, or aren't being reported. Yhere may have been nothing left to record some of the conditions leading up to the explosions due to loss of AC and DC power.

 

[clancy688]

Fukusjma deliberately opened holes in unit 2 so they could spray water into the spent fuel pool. The blowout panels may not have been close enough to the pool.

There's one thing bugging me for weeks regarding this opening of holes... how exactly did they manage to do that?
I mean, they had to remove one of those big concrete panels (sat images show, that there's one panel missing on the east side), but I don't see how that would've been possible. As in Units 1, 3 and 4 there must have been large amounts of hydrogen around. So drilling or using explosives is a no-go. How did they manage it then?

 

[NUCENG]

There's one thing bugging me for weeks regarding this opening of holes... how exactly did they manage to do that?
I mean, they had to remove one of those big concrete panels (sat images show, that there's one panel missing on the east side), but I don't see how that would've been possible. As in Units 1, 3 and 4 there must have been large amounts of hydrogen around. So drilling or using explosives is a no-go. How did they manage it then?

The holes they opened were on the refuel floor. There is only metal siding on the walls there. No concrete panels. Could have been done with a sledge hammer. I am sure they would have carried an explosive atmosphere meter.

 

[Borek]

this is true for the descent phase ... but for the rising phase?

Rising phase is not different. Objects decelerate at 10 m/s² from the moment they were blown up and the force that started them moving stopped to act, movement direction doesn't matter. As it was explained earlier there is a dependence between their speed and drag, which makes both phases slightly different, but there are too many unknowns to reliably calculate anything from this information.