Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[elektrownik]

I want ask about something: what about control rods ? I understand that when reactor cooling stops, temperature is increasing to the point when fuel rods are melting, and entire core is melting, but we know that water is moderator, so it slow down neutrons and then there is chain reaction, so no water no chain reaction, but no water = no cooling, so because this there are boron control rods, when they are inserted into core chain reaction stops, and core can be cooled with water, but what after core melt ? I understand that, size, number, place of control rods are very important. When core is melting control rods are also, so their parameters are changing. So what when we have melted core, I see 2 options: melted core without water and with damaged control rods, can melted core be moderator for itself ? If water slow down neutrons melted uranium also should ? And 2nd option, like 1 but with water, if melted core is not moderator for itself then what when water hit melted core with damaged control rods ? It will slow down neutrons ? More water = more chain reaction ?

 

[MadderDoc]

Regarding Unit 3 imploding.
My physics teacher reckoned that the product of a hydrogen/oxygen burn in our classroom (he was a great Physics teacher) would be 1cc of water. I.e. a pretty good vacuum - if it condenses.

So, perhaps it is natural that we should see some signs of an implosion as the volume that was occupied by all the hydrogen and oxygen before the explosion has effectively shrunk to nearly zero.

I think in the early phases of the event, during which time it must be that some see signs of an implosion, the water would likely still be mainly as vapor. The _first_ we see of the event is something shooting out from the building, which of course is the opposite of an implosion. But a fraction of a second later we get the evolution of the rising cloud, and that by its nature does produce a suction effect.

During the first few seconds of the evolution of the cloud over unit 3, it is rising as a parcel of extremely unstable air, with a speed of about 70 m/s or more, comparable to what we see in supercells. A strong updraft of air will naturally produce strong horizontal movement of air at its base, going towards the center of the updraft.

In the video we clearly see this effect shortly after the appearance of the rising cloud over the building: the dust produced by the blast that is spreading around the building, suddenly appears to be sucked back into it.

 

[Bandit127]

For gaseous water to condense it has to be cooled down. I doubt it had a chance to get below 100 deg C in the explosion time scale.

It doesn't need to get below 100°C.

For example, the top entry on http://www.simetric.co.uk/si_steam.htm" , steam to water volume is ~1603:1, so even at 120 Bar (and assuming a stoichiohometric atmosphere - highly unlikey I know) the resulting pressure would be 0.07 Bar(a) or -0.94 Bar(g).

I don't have any idea what the temperatures and pressures were, but I think it is likely that a hydrogen explosion could pull at least a partial vacuum behind it.

 

[Rive]

... what when water hit melted core with damaged control rods ? It will slow down neutrons ? More water = more chain reaction ?

There are too much hits for 'reflooding recriticality' documents to link them here...

 

[Borek]

It doesn't need to get below 100°C.

Yep, in high pressures.

I don't have any idea what the temperatures and pressures were, but I think it is likely that a hydrogen explosion could pull at least a partial vacuum behind it.

I don't know details as well, but my feeling is that during explosion temperature is high enough to not allow condensation, and after the explosion (that is, when the gas expands and walls are destroyed) pressure inside is already down to atmospheric, so you need to get below 100 deg C. And the cooling process will be way too slow to create implosion.

Note: I am not stating there was no implosion, I am stating I don't believe condensation was behind.

 

[~kujala~]

The gate broken theory is interesting, but it seems to contradict with other observations.

I was satisfied with your explanations.

One additional check one could do is to put the thermal image of the unit 4 on top of this picture, in same direction and proportion:

https://www.physicsforums.com/attachment.php?attachmentid=35237&d=1304674683

If the gate is broken there should be a larger area of warm water than with gate functioning and this larger area could perhaps be seen in the thermal image.

I think the thermal image of the unit 4 has been analyzed at some point, but perhaps not on top of the above picture.

One other notice: TEPCO's thinking has perhaps gone the same way and that's why they don't feel the need to check inside unit 4 any more. As far as I have understood TEPCO has only checked the premises below SFP 4 to see if SFP is leaking:

The company checked the reactor facilities, suspecting water might be leaking from the pool, but cannot confirm water leakage into the bottom structures of the reactor building.

http://www.yomiuri.co.jp/dy/national/T110428006723.htm

I think if they still suspected that SFP is leaking to RPV they would also have to check RPV for leaks and it would require some additional checks. So my understanding is that they have only checked the reactor building for SFP leaks, so far, which is a different thing than to check the reactor building for SFP + RPV leaks. Or is it?

 

[Bandit127]

Yep, in high pressures.



I don't know details as well, but my feeling is that during explosion temperature is high enough to not allow condensation, and after the explosion (that is, when the gas expands and walls are destroyed) pressure inside is already down to atmospheric, so you need to get below 100 deg C. And the cooling process will be way too slow to create implosion.

Note: I am not stating there was no implosion, I am stating I don't believe condensation was behind.

I respect your opinion. I will park my hypothesis in lieu of further data and hope we can continue this discussion in the unlikely event that we ever get it.

 

[bytepirate]

There are too much hits for 'reflooding recriticality' documents to link them here...

slightly offtopic maybe, but a very useful google feature:

you can search in a timeframe. e.g searching all documents indexed before the tsunami, add 'daterange:0-2455631' to your query (without the quotes)

details here: http://jwebnet.net/advancedgooglesearch.html#advDateRange

 

[bytepirate]

How about transient criticalities creating new decay products?

IF you trust the readings of 130 Sv/h that could be an explanation.

what i was trying to say in my original post was: a core melt of 100% might be possible, a core melt of *more than* 100% is certainly not.

 

[TCups]

REGARDING ALLEGED IMPLOSION AT BUILDING 3

Let me say it unambiguously. I do not think implosion occurred at Bldg 3 (or elsewhere). All photographic evidence I have seen (and I have studied it in great detail) suggests violent explosion and violent explosion only. The photographic evidence shows that the blow out panels were blasted outward with great force, the roof was blown upward and off the building, and something heavy fell on the northwest corner of Bldg. 3 after the initial explosion. I have seen no compelling photographic evidence to the contrary.

I do not think that either chemical implosion or negative pressure from Venturi effect or any other negative pressure theory accounts for any of the visible damage I have seen. I do not believe that the video of the explosion of Unit 3 shows implosion.

The one possible effect of negative pressure effect I have speculated on is this: that negative pressure at and around the epicenter of the Bldg. 3 explosion might have had some effect on the distribution of hydrogen gas leaked into Bldg. 4 prior to the explosion at Bldg. 4, specifically, the potential of pulling more hydrogen into the lower portion of Bldg 4 prior to its explosion.

Bldg. 4 remains the enigma of the explosions, IMO. If hydrogen was the fuel for the explosion, how did it get into the lower portions of Bldg 4?

 

[Ms Music]

I applied for registration at that site (my Google translator does a pretty good job.)

But they indicate that their data begins at 2.5 and what we are looking for may be a lower energy than that.

Also their registration process had me OK to this:
"Users are strictly prohibited to create and re-distribute any duplication."

The use of the words "strictly" and "any" would seem to preclude even posting their info here.

What we really need is a geologist type who accesses this kind of data in a normal day's work.

Or find the webicorders? It is harder to "guesstimate" magnitude, but you can at least visually see the exact time that something was felt/recorded, and estimate magnitude based on the size of the ...squiggle?... This map shows the locations, so if you can find the webicorder information, you only need to check the few sites right near the plant. http://www.fnet.bosai.go.jp/st_info/map.php?LANG=en I just can't find the data... Webicorders may be called something else in Japan?

BTW, from the fnet link (right below the map and webicorder graph) says this:

■ Important
When you use the broadband data recorded in the F-net network and make a presentation or publication, you are requested to ACKNOWLEDGE THE DATA SOURCE and to register your presentation or publication on our page.

so you should be good if you post your source, acknowledge them, and notify them. But I could be wrong... '-) But since all you are trying to do is find a tremor at a specific time, instead of making a presentation or publication, I would personally think it is okay. But always best to check first.

 

[unlurk]

If hydrogen was the fuel for the explosion, how did it get into the lower portions of Bldg 4?

I'll offer a hypotheses:

Hydrogen didn't get to the lower levels, but overpressure from the blast higher in the building found its way down to level 1.

This was not a typical explosion. An explosion in most of our experience has a small source: a dynamite explosion is what most people would visualize as an "explosion."

But in unit 4, the explosive charge was widely dispersed (this is a very large building) and was riding on a cushion of air below it.

The ignition of the hydrogen turned building 4 into a pressure vessel.
http://en.wikipedia.org/wiki/Pressure_vessel

 

[Jorge Stolfi]

REGARDING ALLEGED IMPLOSION AT BUILDING 3
I do not think implosion occurred at Bldg 3 (or elsewhere). All photographic evidence I have seen ... suggests violent explosion and violent explosion only...

My impression too, for whatever it is worth.

and something heavy fell on the northwest corner of Bldg. 3 after the initial explosion.

Do you say that because of damage to the service floor slab? Couldn't that be due to an explosion in the 4th storey (below the service floor)? It was forceful enough to blast through the walls, which are fairly thick on that floor. Also it seems to have broken off the NW corner of the steam-dryer pool, which has thick walls too.

If hydrogen was the fuel for the explosion, how did it get into the lower portions of Bldg 4?

See if this makes sense: although H2 is quite a bit lighter than air, it will of course mix with it over time. Mixing within the service storey may be fast, since the heat generated by the SPF in one corner should set up strong convention currents there. Then, for each volume of H2 that is produced, an equal volume of air+H2 mixture will be pushed down the elevator opening ---since the only exit for the air is the ground floor entrance. Thus each floor below service level will be filled in turn with air+H2 mixture, from the top down.

 

[razzz]

I'll offer a hypotheses:

Hydrogen didn't get to the lower levels, but overpressure from the blast higher in the building found its way down to level 1.

This was not a typical explosion. An explosion in most of our experience has a small source: a dynamite explosion is what most people would visualize as an "explosion."

But in unit 4, the explosive charge was widely dispersed (this is a very large building) and was riding on a cushion of air below it.

The ignition of the hydrogen turned building 4 into a pressure vessel.
http://en.wikipedia.org/wiki/Pressure_vessel

That would make sense for Unit 4 as the construction design change seems to make the frame and skin retain pressure a little longer than you would like to see before it releases and there was no working core to vent in that one while certain pathways might be open during the remodel.

 

[Ms Music]

Unlurk - I found the webicorders! I think what you need is the HRO and KSK recorders (located under Tohoku region). It appears fairly easy to maneuver through past charts by changing the date, but I don't have time to play. I have to leave work shortly, and must actually finish my work. I will actually attempt to get online at home, but don't count on it. Family keeps me pretty busy!

Have fun with the data.

edit: oops! http://www.fnet.bosai.go.jp/waveform/?LANG=en

 

[razzz]

REGARDING ALLEGED IMPLOSION AT BUILDING 3

Let me say it unambiguously. I do not think implosion occurred at Bldg 3 (or elsewhere). All photographic evidence I have seen (and I have studied it in great detail) suggests violent explosion and violent explosion only. The photographic evidence shows that the blow out panels were blasted outward with great force, the roof was blown upward and off the building, and something heavy fell on the northwest corner of Bldg. 3 after the initial explosion. I have seen no compelling photographic evidence to the contrary.

I do not think that either chemical implosion or negative pressure from Venturi effect or any other negative pressure theory accounts for any of the visible damage I have seen. I do not believe that the video of the explosion of Unit 3 shows implosion.

The one possible effect of negative pressure effect I have speculated on is this: that negative pressure at and around the epicenter of the Bldg. 3 explosion might have had some effect on the distribution of hydrogen gas leaked into Bldg. 4 prior to the explosion at Bldg. 4, specifically, the potential of pulling more hydrogen into the lower portion of Bldg 4 prior to its explosion.

Bldg. 4 remains the enigma of the explosions, IMO. If hydrogen was the fuel for the explosion, how did it get into the lower portions of Bldg 4?

You didn't account for the heat generation. The dust cloud at ground level pretty much stays in the general area with the majority going up even initially overcoming the wind shear until the column grows. And I'd give you the hydrogen explosion even if the containment vessel was exhausting during much of the event to therefore feed the column, still doesn't explain the source of the heat. Besides aerosols venting, I wonder if particulates are being exhausted to form some type of really volatile mix since the Unit 3 core is pretty much wasted at that point in time.

 

[pdObq]

Yes, I saw also that on Mark I reactors (and maybe Mark II, not sure) that the name used was "blow out panel", which supposes some "intention" by design, but...

I found an original study (1986) on this subject of "secondary containment", didn't read it yet (I'm behind a lot of readings to do...) but it seems very well documented. It's called "The role of BWR MK I secondary containments in severe accident mitigation" an you can get the pdf from this page:

http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=6957980

After looking a bit closer at that document it really seems that the blowout panels they are talking about are not originally intended to reduce the effects of a hydrogen explosion. I found that a probably more elaborate version of that article is published in Nuclear Engineering and Design, vol. 120, p. 75 (1990) (http://dx.doi.org/10.1016/0029-5493(90)90286-7 ). However, my university doesn't have access to that journal prior to 1995.

 

[NUCENG]

According to the World Nuclear Association TEPCO had upgraded seismic design basis earthquake to 600 Gal in 2008. This means they may not have exceeded the design basis earthquake for safe shutdown. The March 11, 2011 earthquake PGA was 507 Gal. Previous information was that the Fukushima design basis was 449 Gal.

The WNA article
http://www.world-nuclear.org/info/inf18.html
was updated 4/23/2011.

 

[pdObq]

Woud it have helped if the walls were like those of #1? My guess is no. Note that the explosion in #4 was violent enough to shatter the massive concrete pillars on the south side, even though the roof above offered a path of lesser resistance.

Moreover, I would guess that part of the explosion in #4 occurred in floors 3 and 4, below the service floor. Yet there are only a few relatively small openings between the floors. Presumably the hydrogen had time to spread through the whole building before it ignited. The fact that we see no damage to the lower floors of #1 probably means that the explosion happened when most of the hydrogen was still in the service area.

The generic BWR design has two blowout panels on the refueling floor. They are ddesigned to open at low pressures (inches of water) during steam leaks or breaks or during negative pressures such as a tornado. The idea that they would most readily blow out in an explosion does not take inertia into account. A very rapid pressurization (explosion) does not give the panel enough time to move out and open the vent path before overpressurizing the remainder of the walls. In short the blowout panels are not useful during a hydrogen explosion.

I'll offer a hypotheses:

Hydrogen didn't get to the lower levels, but overpressure from the blast higher in the building found its way down to level 1.

This was not a typical explosion. An explosion in most of our experience has a small source: a dynamite explosion is what most people would visualize as an "explosion."

But in unit 4, the explosive charge was widely dispersed (this is a very large building) and was riding on a cushion of air below it.

The ignition of the hydrogen turned building 4 into a pressure vessel.
http://en.wikipedia.org/wiki/Pressure_vessel

I found an interesting article titled "Simulation of hydrogen deflagration and detonation in a BWR reactor building" in Nuclear Engineering and Design, Vol. 211, p. 27 (2002) [http://dx.doi.org/10.1016/S0029-5493(01)00443-5 ]. (This one my university has a subsription for, yeahee...) Here's the abstract:

A systematic study was carried out to investigate the hydrogen behaviour in a BWR reactor building during a severe accident. BWR core contains a large amount of Zircaloy and the containment is relatively small. Because containment leakage cannot be totally excluded, hydrogen can build up in the reactor building, where the atmosphere is normal air. The objective of the work was to investigate, whether hydrogen can form flammable and detonable mixtures in the reactor building, evaluate the possibility of onset of detonation and assess the pressure loads under detonation conditions. The safety concern is, whether the hydrogen in the reactor building can detonate and whether the external detonation can jeopardize the containment integrity. The analysis indicated that the possibility of flame acceleration and deflagration-to-detonation transition (DDT) in the reactor building could not be ruled out in case of a 20 mm2 leakage from the containment. The detonation analyses indicated that maximum pressure spike of about 7 MPa was observed in the reactor building room selected for the analysis.​

I only skimmed over the article and I am not really familiar with combustion physics, but as far as I understand from it, the oxygen-hydrogen mixture ignites at one point, then the flame front spreads and gets faster and faster (deflagration?) until it becomes supersonic and a shockfront is formed (detonation?) which is basically the explosion (please correct me if this terribly oversimplified). The shockfront or wave is what causes the damage. They have some nice images in that article showing the simulated pressure distributions and how the shockwave spreads and gets reflected by the walls. They also give some numbers for the pressures that are exerted on the walls by the shockwaves.

This seems to support the theory of a detonation in the upper building, and shockwaves traveling down into the lower floors. I guess thinking of the explosion as happening everywhere at the same time, where there is the proper gas mixture, is oversimplified.

From this picture, I agree that two blowout panels in the structure as units 2-4 have are not useful to divert the effects of a hydrogen explosion. But I think if the walls had been metal just as in unit 1, the effect of the blast onto the building below the service floor would have been less. The shockwave should be reflected from the metal panels which are flying away much less than from the concrete panels and especially the concrete pillars. From the fact that the pillars fell we can see that the pressure buildup onto them stemming from the shockwave must have been huge. But since they are rather heavy objects the reflections from the pillars must have been quite devastating shockwaves too.

 

[pdObq]

Regarding Unit 3 imploding.

If my understanding of explosions is right, a chemical explosion is a rapid combustion reaction that turns (typically) solids or liquids into gasses and creates heat. The rapid expansion of the gasses creates a shockwave that can be subsonic (I think this is Gunderson's 'deflagration') or supersonic ('detonation').

Supersonic detonation occurs when the reaction is perpetuated by the shockwave compressing chemicals to the point that they spontaniously combust.

In a normal 'explosion', we would expect the solids/liquids to expand in volume by orders of magnitude as they turn into gasses. (I only know liquid nitrogen off the top of my head, but that expands in volume by about 670 times at 1 bar).

So a normal explosion will have gas that has been expanded behind the shockwave from solids/liquids that provided the 'fuel' for the explosion.

However, a hydrogen/oxygen explosion starts out as a gas. The shockwave will propogate from the ignition point as a normal explosion would, but the reaction leaves H₂O.

My physics teacher reckoned that the product of a hydrogen/oxygen burn in our classroom (he was a great Physics teacher) would be 1cc of water. I.e. a pretty good vacuum - if it condenses.

So, perhaps it is natural that we should see some signs of an implosion as the volume that was occupied by all the hydrogen and oxygen before the explosion has effectively shrunk to nearly zero.

Oh, sorry, I should have quoted you in my post above about the deflagration/detonation/shockwaves. Regarding the vacuum and implosion I don't agree. If H2 and O2 gas and H2O gas were at the same temperature and pressure after the reaction as before then the volume should be reduced to 2/3 (unless I can't count to 3). However, there is a lot of energy released so the H2O gas should be at a much higher temperature than before, so that the volume at the same pressure should still be larger than before. Also, if what you are saying would happen, then the space shuttle main engine would only have a stream of water dripping out... ;)

 

[unlurk]

Unlurk - I found the webicorders! http://www.fnet.bosai.go.jp/waveform/?LANG=en

Great job, I believe you found the right place.

But all the sites in Japan are reporting "plot not found" for the 12th through the 15th.

Too bad so sad, it looks like they didn't have battery backup.Edit: see my post to zapperzero, Hirono station did report on the 15th.

 

[NUCENG]

I found an interesting article titled "Simulation of hydrogen deflagration and detonation in a BWR reactor building" in Nuclear Engineering and Design, Vol. 211, p. 27 (2002) [http://dx.doi.org/10.1016/S0029-5493(01)00443-5 ]. (This one my university has a subsription for, yeahee...) Here's the abstract:

A systematic study was carried out to investigate the hydrogen behaviour in a BWR reactor building during a severe accident. BWR core contains a large amount of Zircaloy and the containment is relatively small. Because containment leakage cannot be totally excluded, hydrogen can build up in the reactor building, where the atmosphere is normal air. The objective of the work was to investigate, whether hydrogen can form flammable and detonable mixtures in the reactor building, evaluate the possibility of onset of detonation and assess the pressure loads under detonation conditions. The safety concern is, whether the hydrogen in the reactor building can detonate and whether the external detonation can jeopardize the containment integrity. The analysis indicated that the possibility of flame acceleration and deflagration-to-detonation transition (DDT) in the reactor building could not be ruled out in case of a 20 mm2 leakage from the containment. The detonation analyses indicated that maximum pressure spike of about 7 MPa was observed in the reactor building room selected for the analysis.​

I only skimmed over the article and I am not really familiar with combustion physics, but as far as I understand from it, the oxygen-hydrogen mixture ignites at one point, then the flame front spreads and gets faster and faster (deflagration?) until it becomes supersonic and a shockfront is formed (detonation?) which is basically the explosion (please correct me if this terribly oversimplified). The shockfront or wave is what causes the damage. They have some nice images in that article showing the simulated pressure distributions and how the shockwave spreads and gets reflected by the walls. They also give some numbers for the pressures that are exerted on the walls by the shockwaves.

This seems to support the theory of a detonation in the upper building, and shockwaves traveling down into the lower floors. I guess thinking of the explosion as happening everywhere at the same time, where there is the proper gas mixture, is oversimplified.

From this picture, I agree that two blowout panels in the structure as units 2-4 have are not useful to divert the effects of a hydrogen explosion. But I think if the walls had been metal just as in unit 1, the effect of the blast onto the building below the service floor would have been less. The shockwave should be reflected from the metal panels which are flying away much less than from the concrete panels and especially the concrete pillars. From the fact that the pillars fell we can see that the pressure buildup onto them stemming from the shockwave must have been huge. But since they are rather heavy objects the reflections from the pillars must have been quite devastating shockwaves too.

I have seen a number of statements regarding supersonic shock waves in an explosion on this thread. I know jet aircraft and bullets exceed the sonic velocity, but they start with a propulsion source capable of breaking through the sonic barrier. I had been wondering if an explosion pressure wave can really become supersonic. In the explosion of unit 1 you can actually see the pressure wavefront expanding above the building ahead of the steam/debris cloud.

 

[pdObq]

And there would be need for clearing 'debris under the big equipment hatch'. This would seem to indicate opening a hatch somewhere below the level of the service floor in one of the walls. The north and the west wall seem the likely candidates since the east and the south walls have attached buildings.

In the west wall there is a clear signature of a small hatch above service floor level and a faint signature of a larger rectangular shape below it, with two pipes? sticking out from the wall above it. Otoh, below there is rather more equipment and small buildings than debris.

The north wall is hard to come by good photos of, from what I have seen no signature of any openings in the wall can be discerned. Otoh at the foot of this wall there is not much but debris, and probably relatively high activity debris to boot.

See attachments

I bet they are talking about the personnel hatch/airlock and the equipment hatch between primary and secondary containment. Opening those seems scary indeed...

Personnel hatch/Airlock:

http://www.nucleartourist.com/systems/cntm2.htm

http://www.houseoffoust.com/fukushima/tepco_pics/R1_containmentdoor2.jpg
http://www.houseoffoust.com/fukushima/tepco_pics/R1_containmentdoor1.jpgEquipment hatch (Browns Ferry):

http://img.ibtimes.com/www/data/images/full/2011/04/28/92747-the-concrete-hatch-closed-on-the-unit-1-reactor.jpg
http://img.ibtimes.com/www/data/images/full/2011/04/28/92760-the-containment-door-of-the-unit-2-reactor.jpg

Attached is an image of Browns Ferry under construction with assumed position of the hatches circled.

EDIT: Otoh it would not make any sense to open these hatches if they are planning to flood the drywell ...

EDIT2: Please see my edit of post #6065. They do not mean the hatches I have shown here. Pheww...

 

[NUCENG]

I bet they are talking about the personnel hatch/airlock and the equipment hatch between primary and secondary containment. Opening those seems scary indeed...

Personnel hatch/Airlock:

http://www.nucleartourist.com/systems/cntm2.htm

http://www.houseoffoust.com/fukushima/tepco_pics/R1_containmentdoor2.jpg
http://www.houseoffoust.com/fukushima/tepco_pics/R1_containmentdoor1.jpg


Equipment hatch (Browns Ferry):

http://img.ibtimes.com/www/data/images/full/2011/04/28/92747-the-concrete-hatch-closed-on-the-unit-1-reactor.jpg
http://img.ibtimes.com/www/data/images/full/2011/04/28/92760-the-containment-door-of-the-unit-2-reactor.jpg

Attached is an image of Browns Ferry under construction with assumed position of the hatches circled.

EDIT: Otoh it would not make any sense to open these hatches if they are planning to flood the drywell ...

I agree with your identification of the personnel hatch and equipment hatch on the Browns Ferry Pic.

 

[AntonL]

I don't know details as well, but my feeling is that during explosion temperature is high enough to not allow condensation, and after the explosion (that is, when the gas expands and walls are destroyed) pressure inside is already down to atmospheric, so you need to get below 100 deg C. And the cooling process will be way too slow to create implosion.

Note: I am not stating there was no implosion, I am stating I don't believe condensation was behind.

Think of an explosion as air moving away in every direction radiating from the explosion centre. Once the expansion caused by heating phase is over, the air keeps on moving due to kinetic energy, this results in a under pressure at the explosion centre


below simulation of an hydrogen explosion at a hydrogen refuelling station, an under pressure immediately follows the over pressure.

[PLAIN]http://k.min.us/invQiO.JPG

That a hydrogen explosion is followed by an implosion I have speculated in https://www.physicsforums.com/showpost.php?p=3199497&postcount=641"

I now have found the proof in this document http://www.gexcon.com/doc//PDF files/Middha_Hansen_CFD_09.pdf see pressure graphs page 3 of 8

 

[zapperzero]

Implosion

@NUCENG: of course the pressure front can go supersonic. It's called a detonation. Obstacles (choked flow) can make a reaction front go supersonic even if it was not, in the beginning.

Now, fwiw, my take on implosion:

a. I don't see it in the video
b. fancy mechanisms are not required to cave in such a building. A regular explosion inside will do.
c. blast waves can be reflected off nearby buildings. Perhaps this is what you are seeing?
d. Long pulse duration + high overpressure is a recipe for serious vacuum. Light debris may get sucked back in, then ride up the thermal (fireballs are good at radiating heat)

http://www.gexcon.com/handbook/GEXHBcontents.htm

esp. chapters 7 (detonation) and 10 (gas explosions in buildings).

 

[razzz]

They are planning to flood Unit 1 Primary Containment aka Drywell...What could possibly go wrong?

http://atomicpowerreview.blogspot.com/"

-TEPCO has responded to NISA's request regarding the safety of flooding the dry well of No. 1 plant. According to the report (I've read it) there will be no hazards to the dry well or building structurally. NHK has reported that this reactor plant's dry well and reactor pressure vessel volume will require about 7400 tons of water to be added to cover the fuel. TEPCO assures that the building will hold against the originally designed seismic parameters even with the added water mass.

-The air filtration equipment has been installed at No. 1 unit preparatory to making the environment habitable for long enough periods to perform necessary work. This will take about three days' worth of operation to reduce the airborne inside No. 1 reactor building to levels NISA is comfortable with for sustained entry.

-Water injection rate at No. 3 plant has been increased slightly to mitigate a slow temperature rise; this is the non-specific flow rate increase reported here earlier in the week.

-TEPCO has stated that the decay heat removal required for No. 1 plant .. to be dissipated by the partly "rigged," partly installed system .. amounts to about a 1500 kilowatt rating and will require about 100 tons of water per hour.

9:30 PM Eastern Thursday 5/5
ATOMIC POWER REVIEW

 

[ernal_student]

They are planning to flood Unit 1 Primary Containment aka Drywell...What could possibly go wrong?

A lay person's questions: What information is available about the approximate weight of the structure under normal operating conditions? Are the foundations (and other relevant parts of the structure) really designed to handle some 7000 tons of added weight?

 

[pdObq]

I agree with your identification of the personnel hatch and equipment hatch on the Browns Ferry Pic.

Meanwhile I think (and hope) TEPCO is probably not referring to these hatches. From their presentation it looks more like they mean some airlock in between the reactor building and the turbine building. But then I don't know why they are so concerned about opening it. They already had robots and people inside the reactor building, so at some point they must have gone through an airlock. Or maybe they are concerned about opening both doors of that airlock at the same time, which they haven't done so far? The "big equipment hatch" that they are talking about might also be in between the reactor and turbine buildings which would probably make more sense. Or could it be related to the refueling tunnel/entrance on the W side opposite the turbine building?

On the other hand TEPCO mentioned checking or intstalling new RPV gauges. For that they probably would have to access primary containment somehow? Or can that be done from the outside (= reactor building = secondary containment)?

EDIT: Ok, the presentation in the attachement of https://www.physicsforums.com/showpost.php?p=3286021&postcount=5951" explains pretty exactly what they are planning to do, showing the location of the airlock between the R/B and the turbine bldg. And yes, with big equipment hatch they do mean the refuelling tunnel. There's a sketch of it in there as well.

 

[zapperzero]

March 15 (day of blast at unit 4)

Daily plot from Hirono station

http://www.fnet.bosai.go.jp/waveform/view.php?plot=1day&code=HRO&comp=Z&tm=2011031500&LANG=en

 

[razzz]

A lay person's questions: What information is available about the approximate weight of the structure under normal operating conditions? Are the foundations (and other relevant parts of the structure) really designed to handle some 7000 tons of added weight?

You'll just have to take the news release at face value and that TEPCO/Japan knows what they are doing.

I'm sure the foundation on bedrock can handle the weight and the vessel can hold the water, it's any earthquakes and explosions that are hard to factor.

 

[AntonL]

SPF-4 and Hydrogen Production

The puzzle how the Hydrogen in reactor 4 building was generated has not been solved.

That the fuel pool boiled dry such that overheated Zirconium steam reaction could take place
is very improbable due to the mass of water involved and not enough heat available to boil it
away. https://www.physicsforums.com/showthread.php?p=3244793#post3244793"
(We can also discard the idea of double decking as postulated in that post)

Furthermore should the pool have boiled dry this would contradict the Tepco analysis of
SFP-4 water and their conclusion that fuel rod damage is slight. (possible some fuel rods
broken by falling objects into the pool)

We have not discussed the possibility of radiolysis of water into Hydrogen an Oxygen.
[PLAIN]http://k.min.us/in0vfm.JPG
(extracted from Light Water Reactor Hydrogen Manual by Allen L Camp et al)
Under normal circumstance when the water is not boiling the Hydrogen and Oxygen
recombine shortly after the radiolysis event and as such of no concern, however once the
water is boiling the H2 and O2 are carried away by the steam and the amount of Hydrogen
produced for a 3300MW(Th) reactor is tabulated below
[PLAIN]http://k.min.us/jn0vjq.JPG

Now SPF-4 contained the full load of reactor 4 fuel and 106 days old (nearly 10⁷ seconds
at time of explosion, and assuming a Hydrogen production rate of 0.001 Kg/s and scaled
down to 2380MW would result in 62kg of Hydrogen being produced in 24 hours but as the
pool boiled for at least 48 to 60 hours some 120 to 150kg of Hydrogen would have been
released.

Is this enough for the damage we observe?

 

[pdObq]

Think of an explosion as air moving away in every direction radiating from the explosion centre. Once the expansion caused by heating phase is over, the air keeps on moving due to kinetic energy, this results in a under pressure at the explosion centre

below simulation of an hydrogen explosion at a hydrogen refuelling station, an under pressure immediately follows the over pressure.

@NUCENG: of course the pressure front can go supersonic. It's called a detonation. Obstacles (choked flow) can make a reaction front go supersonic even if it was not, in the beginning.

Now, fwiw, my take on implosion:

a. I don't see it in the video
b. fancy mechanisms are not required to cave in such a building. A regular explosion inside will do.
c. blast waves can be reflected off nearby buildings. Perhaps this is what you are seeing?
d. Long pulse duration + high overpressure is a recipe for serious vacuum. Light debris may get sucked back in, then ride up the thermal (fireballs are good at radiating heat)

http://www.gexcon.com/handbook/GEXHBcontents.htm

esp. chapters 7 (detonation) and 10 (gas explosions in buildings).

PreS: I think I am spending too much time in writing a post reply. I just got timed out again and lost all that I had written. And this time I didn't do the ctrl-c. ARGH! So I try to be quicker and more concise this time...

Yes, that handbook seems like a nice resource. There is also a wikipedia article on the deflagration to detonation transition, http://en.wikipedia.org/wiki/Deflagration_to_detonation_transition, that cites that handbook. There are also a lot more combustion and explosion related articles on wikipedia.

That handbook also has a section on explosion relief panels/walls. So, my conclusion is that the metal walls of the unit 1 service floor really did help to minimize the damage from the explosion, whether it was intended or not. The concrete pillars and wall panels in units 3 and 4 did not serve that function and maybe even made the explosion worse by back-reflecting the blast wave into the building and by making it go super-sonic if it hadn't already been (see zapperzeros comment about obstacles).

As an aside regarding the damage to the wall panels below the service floor on unit 3 looking from the east: It almost looks like when the upper part of the wall flew apart, it peeled away with it also the lower panels as the whole thin outer concrete wall seems to have shared one large rebar mat.

 

[unlurk]

Daily plot from Hirono station

http://www.fnet.bosai.go.jp/waveform/view.php?plot=1day&code=HRO&comp=Z&tm=2011031500&LANG=en

I missed that!

It shows some activity at 6:13 and 20 seconds for about five seconds but KSK reported no data that day and there is nothing from the 14th to compare it to.

But this renews hope that the data may yet be out there.

Thanks zapperzero
Thanks Ms Music

 

[NUCENG]

A lay person's questions: What information is available about the approximate weight of the structure under normal operating conditions? Are the foundations (and other relevant parts of the structure) really designed to handle some 7000 tons of added weight?

Containment flooding is an anticipated plant configuration for severe accidents. I will see if I can find information as to whether that is considered as a configuration for which the plant is seismically qualified. What may not be considered is potential damage to the structure from the earthquake and explosions. During initial consideration of containment flooding in March the NRC personnel reported concerns about flooding with potential damage. I don't remember an explanation why they were concerned

edit: I checked two US plant Safety Analysis Reports : a BWR-3 Mk1, and a BWR-4 Mk1. Both include a containment flooded load case for seismic qualification.