Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[elektrownik]

http://enenews.com/japan-nuclear-experts-fears-corium-not-totally-covered-in-water-at-reactor-no-1-may-only-be-15-inches-deep-even-lower-than-no-2

 

[Yamanote]

http://enenews.com/japan-nuclear-experts-fears-corium-not-totally-covered-in-water-at-reactor-no-1-may-only-be-15-inches-deep-even-lower-than-no-2

I expect a similar situation in all three reactors.

If there is a vessel with (given) holes at the bottom, one can only maintain the waterlevel inside by pouring more water into the vessel than escapes through the holes. Obviously this is not possible at Fukuichi, otherwise they would have flooded the PCVs already. Call it reactor design flaw or not, unless the leaks in the PCVs can be sealed, this situation will not change. And we know that the techniques for that are still under development. There is no quick "plan B", so time has to show us...

 

[MadderDoc]

Thinking the same way. The U3 roof structure collapse and damage to east wall framing may not be caused directly by the explosion at all but indirectly by the structural failure in the NW corner of the RB in turn pulling the roof and east wall down.

One can say a priori, that an explosion within the confines of the building cannot cause the collapse of its roof structure directly. It can cause it only indirectly by removing its supports, or by damaging parts of it such as to make it loose integrity. in any case: to bring the roof structure down, there is only gravity. So no quibble there.

Your suggestion otoh that specifically the damage to the wall framing in the south section of the east wall might have been caused by a gravity pull mediated by the collapsing roof structure appears to be entirely speculative. You make no reference to any supporting evidence for that theory, nor evidence to contradict other possible causes of the damage. And in fact it flies in the face of the evidence.

Here, from a video of the explosion, in the very first frame which indicates something untoward is going on with the building, we see explosive damage being done to the walls in the southern part of the east wall:

In the next frame a huge flame burns out through the southern part of the east wall.

It continues to burn for the next many frames, here still visible after more than half a second into the event:

So why should we think none of that damaged the east wall and the roof beams in this part of the building?

 

[zapperzero]

I find it curious that the hypothesis of possible heat damage to structures in the upper SE corner of Unit 3 is commonly met with disbelief. To me it would seem to be rather the default position that such heat damaged structures should exist in the wrecked building. Indeed were nothing immediately obvious it would make sense to me to look more carefully for evidence of it. Weird then, to experience an urge rather to explain away, or be blind to it.

I can see that the hydrogen explosion made a lot of heat, relatively. I do not see how that brief, intense fireball might have had time to heat up the insides of those rather sizeable steel beams.

I'd expect to see no more than light scouring from heating . Blast effects and the structure tearing itself apart afterwards would seem to me to account in a satisfactory manner for most of the damage.

This is not to say that I don't see how that area might have been very hot for a long period of time (days maybe? as dry steam was being emitted?), leading perhaps to further warping.

 

[MadderDoc]

I can see that the hydrogen explosion made a lot of heat, relatively.

Yes. The hydrogen explosionists appear to claim for their theories the combustion of in the order of magnitude 1000 kg hydrogen. My BOE says that's about 150000 MJ heat of combustion.

I do not see how that brief, intense fireball might have had time to heat up the insides of those rather sizeable steel beams.

I am not sure which brief intense fireball you are referring to. I am talking about the fire phenomenon visible above the south east corner of the building for the better part of one second after the building blew up (or should we say 'started to blow up'? :-) Many burnt fingers have been caused by not realising how little heat it takes to heat iron. We are in the neighbourhood of a few hundred MJ/ton/1000K says my BOE.

So, if the hydrogen explosionists could be so kind as to spare some kg of hydrogen for a http://www.gyldengrisgaard.eu/fuku_docs/20120311193727exp2.jpg , which however was undoubtedly present, and with possibly some effective metal heating hydrogen combustion directed to the part of the building in question.

I'd expect to see no more than light scouring from heating . Blast effects and the structure tearing itself apart afterwards would seem to me to account in a satisfactory manner for most of the damage.

Perhaps. You are not being very specific.

This is not to say that I don't see how that area might have been very hot for a long period of time (days maybe? as dry steam was being emitted?), leading perhaps to further warping.

I'd consider that to be just speculative. I don't think it well fits the evidence.

 

[zapperzero]

I am not sure which brief intense fireball you are referring to. I am talking about the fire phenomenon visible above the south east corner of the building for the better part of one second after the building blew up (or should we say 'started to blow up'?

In the beginning there is an actual round fireball poking out of that corner.

So, if the hydrogen explosionists could be so kind as to spare some kg of hydrogen for a perhaps insignificant fire phenomenon[/url], which however was undoubtedly present, and with possibly some effective metal heating hydrogen combustion directed to the part of the building in question.

Undoubtedly there was some heating. I am "just" saying that the most energy, by far, went into making a pressure wave. Incidentally, its leading edge was very hot also. But the inside of that impressive ball of fire is empty, at very low pressure and relatively cool, the flame front passes over any given thing for only the briefest of moments, because it is supersonic. If you look at the photos more, you will see that there is still some paint, in patches, on even the most corroded, darkened beams. That does not jive with scorching heat.

I'd consider that to be just speculative. I don't think it well fits the evidence.

Me neither. It's just a remote possibility.

 

[MadderDoc]

In the beginning there is an actual round fireball poking out of that corner.

When, in the beginning? Perhaps you can use this as a reference.

Undoubtedly there was some heating. I am "just" saying that the most energy, by far, went into making a pressure wave. Incidentally, its leading edge was very hot also. But the inside of that impressive ball of fire is empty, at very low pressure and relatively cool, the flame front passes over any given thing for only the briefest of moments, because it is supersonic. If you look at the photos more, you will see that there is still some paint, in patches, on even the most corroded, darkened beams. That does not jive with scorching heat.

The visible fire phenomenon is almost entirely outside the building, so only relevant from what it tells us about what's concurrently happening inside the building, e.g. where does the burning substance originate from, what source feeds it, what route did it take from there to erupt on the outside of the building, what were the conditions for damage along that route while it burned.

 

[MadderDoc]

<..>. If you look at the photos more, you will see that there is still some paint, in patches, on even the most corroded, darkened beams. That does not jive with scorching heat.

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.

 

[jim hardy]

i'm way behind you fellows.

I can't rule out the beams having got roasted by hot gas during or afterward. Rust suggests the paint got cooked off.

Still musing on the columns.
The crane rail, so obvious in that photo, ties the columns together for N-S forces. The east ones still standing fairly well retained that alignment.
The west ones did too, from aerial March 20 (2011) shots of them dangling by rebar.
The resolution of those isn't good enough to say whether the rail is still attached to them but it doesn't appear to be laying under the crane ends up on the deck.

If that substantial beam is one continuous rail it'd add some rigidity for E-W forces too, making the columns into a wall-like structure. That could explain why the [STRIKE]east[/STRIKE]west (edit) columns toppled together as a unit. I'd say the [STRIKE]west[/STRIKE]east ones almost did too.

plodding along. if you guys dismiss this as beating the obvious I'm not offended.

visiting kids now and away from my computer else i'd post that 20 march photo..

old jim

 

[MadderDoc]

Still musing on the columns.
The crane rail, so obvious in that photo, ties the columns together for N-S forces. The east ones still standing fairly well retained that alignment.
The west ones did too, from aerial March 20 (2011) shots of them dangling by rebar.
The resolution of those isn't good enough to say whether the rail is still attached to them but it doesn't appear to be laying under the crane ends up on the deck.

If that substantial beam is one continuous rail it'd add some rigidity for E-W forces too, making the columns into a wall-like structure.

It is not a continuous rail, it is in 6 sections corresponding to the wall structure. The sections appear to have been laid out on slip pads on top of the pillar supports. This would seem to be in order to guard against heat expansion's cracking up the building over time, so the rail sections are unlikely to be firmly attached to the pillars. The rails sections from the west wall seem to have just slid off the wall pillars once they landed top down.

 

[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.