Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[zapperzero]

Apparently 'hydrogen explosion' can be used to explain any effect, any degree of damage, and is not supposed to be held to any high evidential standard. Otoh, if there is just a few patches of something looking like paint to be found on a piece of scrap metal, it is concluded that it cannot have been damaged by heat. I wonder if you'd seriously be willing to use that criterium, if you were shown corroded beams with not a speck of paint left, or 'hydrogen explosion' and a bit of handwaving would be used to explain that away too.

I am not saying there was no heat involved. I am saying that the blast bent and scoured those beams. IOW, some of the superficial damage that you see (rusty bits where paint used to be) is caused by heat. The sagging and twisting, it's because of the blast and (afterwards) gravity.

Please, don't tell me you believe those beams were melted into that position.

I mean, sure, there is enough energy in a ton (or even half-ton) of hydrogen to do that. But how was it done? Those beams were not melted one by one with a H-O torch. They were blasted. You can see the blast yourself. Why do you find it hard to believe that it could have bent and twisted steel? Do you not think a pressure spike of 1.5-2 MPa (at least, much higher if reflected) could have done what we are seeing?

Take a look at this, please.
http://www.hysafe.org/download/1009/BRHS_Ch3_Consequences_version 1_0_1.pdf

 

[LabratSR]

Scheduled Access Route for the Robot (Quince 2) of the
Investigation in the TIP Room on the First Floor at Unit 3
Reactor Building, Fukushima Daiichi Nuclear Power Station

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120522_02-e.pdf

 

[MadderDoc]

I am not saying there was no heat involved. I am saying that the blast bent and scoured those beams. IOW, some of the superficial damage that you see (rusty bits where paint used to be) is caused by heat. The sagging and twisting, it's because of the blast and (afterwards) gravity.

Please, don't tell me you believe those beams were melted into that position.

I mean, sure, there is enough energy in a ton (or even half-ton) of hydrogen to do that. But how was it done? Those beams were not melted one by one with a H-O torch. They were blasted. You can see the blast yourself. Why do you find it hard to believe that it could have bent and twisted steel? Do you not think a pressure spike of 1.5-2 MPa (at least, much higher if reflected) could have done what we are seeing?

Perhaps. You are not being very specific, I much prefer to be working from evidence.

I think it is fair to say that the roof construction of Unit 3, or what remains of it is _not_ uniformly damaged, and in that context the SE corner of the construction stands out as being in particularly worse shape. Also it appears to be damaged in ways or degrees we do not see elsewhere. While most parts of the roof construction could well with some mechanic work be reconstructed reusing most pieces, the SE quadrant looks like a scrap the lot job (or whatever of it you can identify) and do a total rebuild.

Likewise, looking at the east wall, or what remains of it, it is not uniformly damaged. The south half of it is the more damaged part. Within the north and the south sections otoh, the damages share a common pattern, as regards e.g. discoloring and concrete matrix degradation. In the north section the roof construction has neatly come unplugged from its sockets on the pillars. In the south section the complete top layer of the pillars with the sockets come off in pieces, and it is not at all clear that anything there became neatly unplugged.

Then of course there is the video evidence, which again indicates a peculiarity, a prominent fire phenomenon, linked to the SE corner of the building.

To be sure 'hydrogen explosion' can go a long way to explain the damages to Unit 3, in general terms. And there are some knobs one can screw on. More hydrogen, more flame front speed, its all on the shelves for the picking. But, what does it do to explain the peculiarities? High on my wishing list would be the explanation of the peculiar damages to the SE corner of the building and its curious coincidence with the peculiar fire phenomenon above that corner, one of the hall marks of the Unit 3 event. While of course the peculiar mushroom cloud and its curious coincidence with a pressure drop in the reactor tops the list..

 

[zapperzero]

Perhaps. You are not being very specific, I much prefer to be working from evidence
Then of course there is the video evidence, which again indicates a peculiarity, a prominent fire phenomenon, linked to the SE corner of the building.

Frames 1-15 in the glydensgaard thing. That's a fireball.

To be sure 'hydrogen explosion' can go a long way to explain the damages to Unit 3, in general terms. And there are some knobs one can screw on. More hydrogen, more flame front speed, its all on the shelves for the picking.

Oh, yes.

But, what does it do to explain the peculiarities? High on my wishing list would be the explanation of the peculiar damages to the SE corner of the building and its curious coincidence with the peculiar fire phenomenon above that corner, one of the hall marks of the Unit 3 event.

The explosion originated in the S-E corner, so I'd expect the peak overpressure to be higher there. The thing you insist on calling a "fire phenomenon" looks to me like your regular run-of-the-mill fireball. Would you say it's something else?

While of course the peculiar mushroom cloud and its curious coincidence with a pressure drop in the reactor tops the list..

Peculiar how? Blasts make mushroom clouds. Bigger the blast, bigger the cloud. 1 ton of hydrogen is nothing to sneeze at.

Ah. The pressure drop. There was a nice theory, back there in the killed explosion thread, as to how the hydrogen explosion may have made a lot of water in the SFP flash-boil, to produce the steam. But maybe it didn't, or not so much. Maybe some pipe broke somewhere, or the reactor cap was jarred, and it burped.

I am in a peculiar situation. I know how to explain, but I don't know that there is a way to make you, or anyone else who has never seen a big (or even moderate) explosion and its immediate effects understand just how destructive they can be.

I am very okay with the hydrogen explosion theory, because of Occam's razor. I'd even be happy with a "mere steam explosion" theory, were it not for the fireball we can so clearly see.

I found this thing, maybe interesting:
http://www.japantimes.co.jp/text/nn20110607a5.html

The chief of the JSDF firefighter crew whose men were injured on the day says they saw 20 mSv/h in the immediate aftermath of the explosion.

 

[MadderDoc]

<..>
The explosion originated in the S-E corner, so I'd expect the peak overpressure to be higher there. The thing you insist on calling a "fire phenomenon" looks to me like your regular run-of-the-mill fireball. Would you say it's something else?

By 'fireball' I would understand a detached roundish area of space with ongoing combustion, drifting by its own inertia and buoyancy. The fire phenomenon over unit 3 otoh appears to be stationary, to have an origin, to shoot out of the building as a jet, and to wax and eventually wane into the smoke, as if its source of fuel was being cut off. Since the phenomenon is not unambiguously a fireball, I prefer not to call it that, until the nature of it has been resolved.

Peculiar how? Blasts make mushroom clouds. Bigger the blast, bigger the cloud. 1 ton of hydrogen is nothing to sneeze at.

I wouldn't _dream_ of sneezing in the presence of 1 ton of hydrogen confined in the upper floors of unit 3. Assuming it is mixed with air, that would be close to stoichiometric, I could get myself killed :-). But seriously, 'Blasts make mushroom clouds. Bigger the blast, bigger the cloud.' doesn't cut it. You've got 1 ton of hydrogen: so how big a mushroom cloud, of which composition, would that be able to produce? Cf. "He who refuses to do arithmetic is doomed to talk nonsense."

<..>

I found this thing, maybe interesting:
http://www.japantimes.co.jp/text/nn20110607a5.html

The chief of the JSDF firefighter crew whose men were injured on the day says they saw 20 mSv/h in the immediate aftermath of the explosion.

Yes, that was an interesting aspect to the story. Funny how in retrospect that JSDF mission has become fuzzily one of "to spray water onto the crippled reactor". In fact the problem was that Tepco was running out of seawater in the backwash pit to inject into the reactor vessel of Unit 3. They had moved the hose to the deepest spot of that pit to be able to get the last drops out of it, while they were desperately trying to secure water, any kind of water to refill the pit. Then in the morning of March 14th, those SDF water supply vehicles arrived, each with 5 cubic meter of fresh water, which it was decided to dump into the backwash pit. The first of these vehicles were about unloading its cargo, when the building exploded.

 

[MadderDoc]

Unit 3 explosion mechanisms (was Re: Japan)

I am very okay with the hydrogen explosion theory, because of Occam's razor. I'd even be happy with a "mere steam explosion" theory, were it not for the fireball we can so clearly see.

Occam's razor does not say that either mere this, or mere that, is to be chosen as the better explanation, simply because it is simpler. What it does, that razor, is to prod kindly not to add to an explanation any complexity which does not add explanatory power. Thus, if you was happy with 'mere steam' then it would be because you already felt it explained things. And if you then saw a fireball, it would be perfectly alright with Occam to make further assumptions to your 'mere steam' theory, modify it, such as to make it explain that fireball too. Unless of course you've found evidence to contradict you present theory, that is another cup of tea.

However, in the present context there seems to be nothing contradictory in having steam as well as hydrogen involved in an explanation of the events in Unit 3. In fact these events played out in the presence of a high grade potential source of both, and with limited opportunity for release of one without the other.

 

[zapperzero]

By 'fireball' I would understand a detached roundish area of space with ongoing combustion, drifting by its own inertia and buoyancy. The fire phenomenon over unit 3 otoh appears to be stationary, to have an origin, to shoot out of the building as a jet, and to wax and eventually wane into the smoke, as if its source of fuel was being cut off.

The shock front pushes the hydrogenated air in front of it away, until there is no more hydrogen (cut off). This is a hydrogen blast, not a puff from your local RenFaire fire-eater.

I wouldn't _dream_ of sneezing in the presence of 1 ton of hydrogen confined in the upper floors of unit 3. Assuming it is mixed with air, that would be close to stoichiometric, I could get myself killed :-).

But seriously, 'Blasts make mushroom clouds. Bigger the blast, bigger the cloud.' doesn't cut it. You've got 1 ton of hydrogen: so how big a mushroom cloud, of which composition, would that be able to produce? Cf. "He who refuses to do arithmetic is doomed to talk nonsense."

Well if I could do it, I would. I can tell you how many tons of water vapor you get from burning a ton of hydrogen and how much volume it would occupy at normal temp and pressure. Would that help?

I cannot tell you what else was in the air inside that building or what else is in the cloud (although I strongly suspect there was a lot of steam from the SFP), I cannot tell you if there was an inversion layer that day or how high it was, I can't tell you the outside temp. I cannot say exactly what the nature of the black smoke is, although I strongly suspect it is powdered ceiling. So... sorry, approximations and guesswork it is.

Yes, that was an interesting aspect to the story. Funny how in retrospect that JSDF mission has become fuzzily one of "to spray water onto the crippled reactor". In fact the problem was that Tepco was running out of seawater in the backwash pit to inject into the reactor vessel of Unit 3. They had moved the hose to the deepest spot of that pit to be able to get the last drops out of it, while they were desperately trying to secure water, any kind of water to refill the pit. Then in the morning of March 14th, those SDF water supply vehicles arrived, each with 5 cubic meter of fresh water, which it was decided to dump into the backwash pit. The first of these vehicles were about unloading its cargo, when the building exploded.

Funny coincidence, that. I wonder if water injection had already stopped.

 

[SteveElbows]

I know its been pretty quiet in terms of news this month, but I am under the impression this will change by the end of the month. I think someone already mentioned the reactor 3 TIP room survey, but there are a few other things happening as well:

There will be a new press tour on Friday which I suppose should give us a few new images. Its likely to focus on reactor 4 again due to ongoing noise about the danger of pool collapse, which continues to cause them PR headaches.

According to a press report that I cannot lay my hands on right now, they have been doing robot gamma camera surveys inside the reactor building to identify containment leak points that will need to be fixed. Data from this survey is supposed to be compiled by the end of May. I believe its for reactor 3 but I need to double-check this detail.

Also I note this report in the business press, but I haven't tried looking for the original source document yet:

http://www.businessweek.com/news/2012-05-24/fukushima-s-estimated-radiation-leak-doubles-versus-government

Tokyo Electric Power Co.’s crippled Fukushima nuclear plant may have released twice as many radioactive particles than Japan’s government estimated, the utility said in a report today.

The Fukushima Dai-Ichi plant may have emitted about 900,000 terabecquerels of the iodine equivalent of radioactive iodine 131 and cesium 137 into the air at the height of the disaster, the utility known as Tepco said today in a statement. The amount is about 2 times more than the 480,000 terabecquerels estimated in February by the Nuclear and Industrial Safety Agency or NISA, the utility said.

 

[zapperzero]

However, in the present context there seems to be nothing contradictory in having steam as well as hydrogen involved in an explanation of the events in Unit 3. In fact these events played out in the presence of a high grade potential source of both, and with limited opportunity for release of one without the other.

We are in violent agreement on this one.

 

[MadderDoc]

The shock front pushes the hydrogenated air in front of it away, until there is no more hydrogen (cut off). This is a hydrogen blast, not a puff from your local RenFaire fire-eater.

Does your observations of this shock front allow you to estimate its speed?

I can tell you how many tons of water vapor you get from burning a ton of hydrogen and how much volume it would occupy at normal temp and pressure. Would that help?

It seems OK, for a starter.

I cannot tell you what else was in the air inside that building or what else is in the cloud (although I strongly suspect there was a lot of steam from the SFP)<..>

Well, perhaps you can think of something. The options for what gases could have been around apart from hydrogen are limited.

Funny coincidence, that. I wonder if water injection had already stopped.

Funny thing is that any source (that I've been able to find) leaves uncertainty as to whether injection to the reactor pressure vessel was ongoing at the time of the explosion. Only thing that is clear is that water transfer to replenish water to the drained backwash pit had been started.

 

[MadderDoc]

We are in violent agreement on this one.

Let's just hasten on then, there's nothing to be learned from violent agreement.

 

[zapperzero]

Does your observations of this shock front allow you to estimate its speed?

Yes. You can estimate it yourself, even, from the video you posted. I'd say it's supersonic, but only just.

It seems OK, for a starter.

14400 cubic meters of saturated steam, or a sphere roughly 15 meters in radius, if I have not misplaced my brains again.

Well, perhaps you can think of something. The options for what gases could have been around apart from hydrogen are limited.

I think it was jim hardy who suggested that because of the decrease in pressure, the SFP may have flash-boiled, releasing huge amounts of steam and nearly emptying itself in the process.

 

[zapperzero]

Scheduled Access Route for the Robot (Quince 2) of the
Investigation in the TIP Room on the First Floor at Unit 3
Reactor Building, Fukushima Daiichi Nuclear Power Station

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120522_02-e.pdf

You'd think by now we'd be able to invent a robot that can twist and pull door handles. Disgusting.

 

[radio_guy]

both quince and the packbot can open doors.

there must be some situation that makes it not ideal for them to do this to have a human go in, open the door then send the robot in?

 

[MadderDoc]

both quince and the packbot can open doors.

there must be some situation that makes it not ideal for them to do this to have a human go in, open the door then send the robot in?

Perhaps somebody can figure out the function of the human from the video of the similar expedition to the TIP room of unit 2:
http://photo.tepco.co.jp/en/date/2012/201203-e/120322-02e.html

 

[jim hardy]

I think it was jim hardy who suggested that because of the decrease in pressure, the SFP may have flash-boiled, releasing huge amounts of steam and nearly emptying itself in the process.

no, i remember that suggestion being made though.
i don't see a mechanism for that much heat transport into pool.
so i didnt comment on it.

my observation was this
if you could get 10^18 neutrons into the fuel that's in the pool
and fuel there had Keff of 0.95 (not unreasonable)
it should make enough heat to boil about a thousand pounds of water into steam, which is a good cloud.
But i couldn't come up with a source of that many neutrons arrviing in pool without an unfortunate and exotic series of events. Even if the core were up in the steam separator region of RPV it's still a couple tenth value thicknesses of concrete from there to pool, and substantial water. At home i have a cross section drawing of the building showing the path.. Looks might unlikely.

So i have settled in with mdoc's 'other source' for steam.
unless you guys find some other evidence like the wall between RPV and SFP to be blown away, which i doubt.

old jim

 

[zapperzero]

no, i remember that suggestion being made though.
i don't see a mechanism for that much heat transport into pool.
so i didnt comment on it.

the pressure inside the blast's fireball is much lower than atmospheric - so water could boil at a much lower temp than the usual hundred celsius. Dunno if anyone's tried anything like this, but it sure would make a fun little experiment.

 

[MadderDoc]

Yes. You can estimate it yourself, even, from the video you posted. I'd say it's supersonic, but only just.

OK, thanks, I'll give it another go, at least now I know there's supposed to be a method.

14400 cubic meters of saturated steam, or a sphere roughly 15 meters in radius, if I have not misplaced my brains again.

Thanks for your efforts, it does not seem to me far off, so I'll go with that. But that's just the water from the combustion. The initial 14400 cubic meters of hydrogen would have come mixed with some air, the nitrogen of which would add to the final volume of combustion products. Air is appr. 80 % nitrogen and 20 % oxygen. So for the complete combustion of 14400 cubic meters of hydrogen we'd need to mix it well, with 2.5 times as much air, for a total of 50000 cubic meter of fuel mixture inside the building.

(Btw, this seems a tight fit for the size of the building, it seems not much more than 1 ton of hydrogen can be realistically imagined to have been combusting inside it)

Anyways, after the combustion of the 50000 cubic meters of fuel mixture, we end up with that volume minus the volume of oxygen consumed = about 43000 cubic meters of combustion gases. (14400 cubic meters of steam mixed with 28800 cubic meters of nitrogen). That would be a sphere roughly 22 meters in radius. But the mushroom cloud is bigger than that. Air, we can entrain some air! However, not too much, entraining air means our cloud looses buoyancy, without which there can be no Rayleigh-Taylor instability, hence no mushroom cloud.

 

[MadderDoc]

the pressure inside the blast's fireball is much lower than atmospheric - so water could boil at a much lower temp than the usual hundred celsius. Dunno if anyone's tried anything like this, but it sure would make a fun little experiment.

Heh. In the old days we had cars with which to do that kind of experiment :-) One learned quickly to protect the hand with a piece of cloth when releasing the lid to depressurise the hot radiator and to do it gently. More excitingly, one could make a swift twist to the lid and jump back. Whoosh!

 

[Joffan]

OK, thanks, I'll give it another go, at least now I know there's supposed to be a method.


Thanks for your efforts, it does not seem to me far off, so I'll go with that. But that's just the water from the combustion. The initial 14400 cubic meters of hydrogen would have come mixed with some air, the nitrogen of which would add to the final volume of combustion products. Air is appr. 80 % nitrogen and 20 % oxygen. So for the complete combustion of 14400 cubic meters of hydrogen we'd need to mix it well, with 2.5 times as much air, for a total of 50000 cubic meter of fuel mixture inside the building.

(Btw, this seems a tight fit for the size of the building, it seems not much more than 1 ton of hydrogen can be realistically imagined to have been combusting inside it)

Anyways, after the combustion of the 50000 cubic meters of fuel mixture, we end up with that volume minus the volume of oxygen consumed = about 43000 cubic meters of combustion gases. (14400 cubic meters of steam mixed with 28800 cubic meters of nitrogen). That would be a sphere roughly 22 meters in radius. But the mushroom cloud is bigger than that. Air, we can entrain some air! However, not too much, entraining air means our cloud looses buoyancy, without which there can be no Rayleigh-Taylor instability, hence no mushroom cloud.

50000 ≈ 37^3 - a bit oversize I'd say but close enough. Hydrogen can still explode even when 50% by volume though.

Don't forget the explosion energy will heat & expand the gases significantly (well, pressurize them first, then expand them). Hydrogen burning in air is up to about 2300K ~ 8x volume at atmospheric, less the decrease from oxygen consumption, -> ~7x, by my rough calculation.

 

[MadderDoc]

50000 ≈ 37^3 - a bit oversize I'd say but close enough. Hydrogen can still explode even when 50% by volume though.

Don't forget the explosion energy will heat & expand the gases significantly (well, pressurize them first, then expand them). Hydrogen burning in air is up to about 2300K ~ 8x volume at atmospheric, less the decrease from oxygen consumption, -> ~7x, by my rough calculation.

Fair enough, but I don't think we can assume the temperature of a dark non-glowing cloud to be 2300K or anywhere near it.

 

[MadderDoc]

In a funny way the video of the Unit 3 explosion indicates the possible behaviour of combustion gases from a hydrogen explosion by its kind exposure to our view of the fire phenomenon in the SE corner -- and the ensuing development of a knob of the condensed steam from that combustion, at the downwind side of the stem of the mushroom cloud.

Unfortunately Internet has been thoroughly cleaned of the best videos of the explosion, but if you can get your hands on one still, and it has more than the first dozen of seconds after the blast, this knob of steam from the explosion in the SE corner can be followed, as it travels downwind along with the mushroom. It stays low, and appears to have little tendency to rise, rather it just slowly grows and thins out by entraining air, and gradually disperses, much like the behaviour of the clouds we saw going with the wind from unit 1.

Image above is the last frame from this Unit 3 explosion animation

 

[r-j]

nuclear plant question

What is the source of the hydrogen that is believed to have caused the explosions?

 

[Most Curious]

What is the source of the hydrogen that is believed to have caused the explosions?

Short answer; Zircaloy cladding of the fuel rods in a steam or water atmosphere and very high temperatures releases a lot of hydrogen.

 

[Joffan]

Fair enough, but I don't think we can assume the temperature of a dark non-glowing cloud to be 2300K or anywhere near it.

No, well, that's full of dust and rubble too by the time we see it, don't forget. The 2300K burn temperature is (1) a maximum and (2) quickly diluted and reduced as the gas expands. It won't have transmitted more than a small fraction of that heat into the debris.

And anyone who knows more about the physics of explosions should jump in and correct me, incidentally, since I'm definitely no expert.

 

[zapperzero]

OK, thanks, I'll give it another go, at least now I know there's supposed to be a method.

I did not mean to be chiding you, sorry. It is simply that you know the size of the building, so you can get a fair estimate of how fast the ball grows because of also knowing at what intervals the frames are taken.

 

[zapperzero]

More excitingly, one could make a swift twist to the lid and jump back. Whoosh!

'Zackly. I don't know if you can get the same effect when you blow the roof off a depressurized equipment hall.

 

[zapperzero]

The initial 14400 cubic meters of hydrogen would have come mixed with some air, the nitrogen of which would add to the final volume of combustion products.

Dunno about that... I just stated the volume of steam at normal temp. That figure implies a rather low partial pressure (iow the air is pre-mixed :).

Also, initially there would have been, oh, however many meters of hydrogen-air mix the building can fit :).

 

[MadderDoc]

No, well, that's full of dust and rubble too by the time we see it, don't forget. The 2300K burn temperature is (1) a maximum and (2) quickly diluted and reduced as the gas expands. It won't have transmitted more than a small fraction of that heat into the debris.

Re - by the time we see it - 'it' being the mushroom cloud, when that would be that we see it. In the initial development of the vertically projected cloud, its upper edge would represent the front of ejected debris. The material to produce the mushroom cloud is of course there too. As the cloud progresses upwards, the debris slows down to eventually, except for the fine dust, start falling back to the ground. It is at this stage the mushroom can be most clearly seen, as it is emerging out of the top of the eruption cloud, steadfastly continuing its buoyancy driven travel upwards.

To illustrate, here's an animation of 17 frames, one for each of the first 17 seconds of the explosion. Images are heavily color enhanced to allow better distinction between the different cloud formations.

 

[SteveElbows]

I see the reactor 3 TIP room investigation was a bit of a failure, due to door etc debris.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120524_06-e.pdf

Given that a human was able to visually inspect one part of the room, I am less than impressed about a lack of photo of this area. It makes me curious about the nature of any debris inside the room.

 

[MadderDoc]

'Zackly. I don't know if you can get the same effect when you blow the roof off a depressurized equipment hall.

I think you are speaking in the context of a shortlived pressure drop below ambient, that would be present in connection with a detonation. But it takes time to nucleate water, that's why it works well to jump back from the radiator in the case of the car. I think to get some steam out of the effect in a pool in depressurised hall, you'd need more than a brief underpressure pulse, something like the permanent decrease of the pressure above the water in the car radiator. Also, you must lower the pressure, such that the new saturation temperature is lower than the temperature of the water. In the case of the pool we are probably looking at a body of water at about 50 deg C, so that is quite some pressure drop that must be maintained.

The theoretical mass of steam that can be produced by the depressuring can be fairly easily estimated. It is directly proportional to the difference between the initial temperature and the boiling temperature at the new lower pressure, and directly proportional to the amount of water present. The proportionality factor is about 0.002K^-1.

Mass(steam)=0.002*(Twater-Tsat)*Mass(water)

Example: You have a pressurised PCV filled with saturated steam and 4000 m3 of liquid water at 150 deg C. Swiftly release the containment lid and jump back a mile. Don't try this at home.

Mass(steam)=0.002*(150-100)*4000 = 400 tons

 

[MadderDoc]

I see the reactor 3 TIP room investigation was a bit of a failure, due to door etc debris.

http://www.tepco.co.jp/en/nu/fukushima-np/images/handouts_120524_06-e.pdf

Given that a human was able to visually inspect one part of the room, I am less than impressed about a lack of photo of this area. It makes me curious about the nature of any debris inside the room.

Weird to see that the door and apparently the door frame has not been blown away, but has been blown inward, into what they call the labyrinth. The implied pressure differential that should have existed to produce that effect is intriguing.

 

[zapperzero]

I think you are speaking in the context of a shortlived pressure drop below ambient, that would be present in connection with a detonation.

Yes.

But it takes time to nucleate water, that's why it works well to jump back from the radiator in the case of the car.

How much time? We have about a second, second and a half to work with, no?

I think to get some steam out of the effect in a pool in depressurised hall, you'd need more than a brief underpressure pulse, something like the permanent decrease of the pressure above the water in the car radiator. Also, you must lower the pressure, such that the new saturation temperature is lower than the temperature of the water. In the case of the pool we are probably looking at a body of water at about 50 deg C, so that is quite some pressure drop that must be maintained.

That's what I meant, when I said this should be experimented upon. But are you sure about the pool water temp? Could easily have been more.

The theoretical mass of steam that can be produced by the depressuring can be fairly easily estimated. It is directly proportional to the difference between the initial temperature and the boiling temperature at the new lower pressure, and directly proportional to the amount of water present. The proportionality factor is about 0.002K^-1.

Mass(steam)=0.002*(Twater-Tsat)*Mass(water)

Example: You have a pressurised PCV filled with saturated steam and 4000 m3 of liquid water at 150 deg C. Swiftly release the containment lid and jump back a mile. Don't try this at home.

Mass(steam)=0.002*(150-100)*4000 = 400 tons

I'm reasonably sure that the RPV didn't have that much water in it, in the event :). Anyways, http://www.spiraxsarco.com/esc/SS_Properties.aspxgives me a saturation temp of 60.something degrees celsius at 0.2 atm absolute. At 7.5 m^3/kg that's... a lot of steam, should the pool boil over. I am not sure how fast it nucleates, though. It should still be reasonably clean at this point, unless crud was thrown in by the earthquake.

 

[zapperzero]

Weird to see that the door and apparently the door frame has not been blown away, but has been blown inward, into what they call the labyrinth. The implied pressure differential that should have existed to produce that effect is intriguing.

The explosion could have done that, because the hydrogen-air mix occupies much more volume than the resulting steam. I can't think of anything else.

 

[MadderDoc]

Dunno about that... I just stated the volume of steam at normal temp. That figure implies a rather low partial pressure (iow the air is pre-mixed :).

Then I am not sure how you arrived at that figure, and how it landed in the right ball-park range for the volume of steam that can be produced from 1 ton of hydrogen. Are you a beginner? :-)

Also, initially there would have been, oh, however many meters of hydrogen-air mix the building can fit :).

Yes, I think we've arrived at something like 50000 cubic meters on that one. It could be less of course, but not significantly more. Once exploded, the combustion gases would come out as clouds from the building, and likely somewhat expanded in volume (due initially to elevated temperature, later due to air entraining). The hydrogen explosionists will necessarily have to claim responsibility for the clouds encircled here under, the mushroomists will have nothing to do with them. The 50000 cubic meters of hydrogen-air mix would seem to suffice to produce those clouds.

http://gyldengrisgaard.dk/fuku_docs/Unit3_hydrogenexplosioncloud.jpg