Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[Astronuc]

Questions: What is radiation in core at max reactor power, what is radiation in core after shutdown, what would be radiation of fuel rod/set from sfp, without water or any other protection ?

In the core at power, the radiation field is so very different than simple radionuclide decay. The thermal and fast neutron fluxes are on the order of 10¹⁴ n/cm²-s. And the gamma and beta radiation is intense.

About 20 years ago, I was involved as a consultant to a utility where they managed to break a fuel rod outside of the core. It had failed during the cycle, and they managed to break it while moving the assembly during the refueling outage. The fuel rod was not discovered until they were draining the cavity above the RPV, and the radiation alarms went off. The operators stopped, reflooded the cavity and went to take a look.

The fuel rod was broken in 4 pieces. The top and bottom sections were about 2 ft each, and there were two 5-ft sections. One section was empty of fuel! It's activity was about 5000 R/hr, IIRC. Another section was about 2000 R/hr. I'd have to dig up my notes - but they were hot. The NRC wanted to know - where did 1 kg of UO2 go!? Well the answer was - it was distributed in the primary system as fuel particles and uranyl ions. The Np-239 in the reactor coolant (as well as increased Xe, Kr, I and Cs) was a really good indication that they had a degraded failure in the core. They just didn't bother to go look for it during the outage.

The senior plant management were fired.

 

[M. Bachmeier]

No - I'm not being ironic. If TEPCO invited me, I'd be on-site ASAP.

Astronuc, as a manager I'm not be surprised but your sentiments. I feel a certain amount of responsibility and commitment to the projects I undertake and am always willing to assume some degree of association and responsibility. No good manager ducks his responsibility, or his ability to ameliorate a site site situation.

 

[Astronuc]

Have I understood you correctly?
You believe that there was no damage to the nuclei in the reactors, and therefore no meltdown?

I believe there is washout and dissolution of the fuel, but not nessarily melting - particularly if there was water in the bottom third of the cores. The question is - was there water in the bottom third of the cores?

 

[rowmag]

Further follow-up (context: cphoenix's superheated steam explosion theory):

Searching through the file finds no other reference to the plastic covering, but some references to fiberscope searches for foreign matter in the assemblies (not much found), but no particular reason given why this should be a MOX-specific issue (to go to NUCENG's query). So perhaps such plastic covering may have been used in SFP4 as well?

I skimmed through a bunch of past press releases on the TEPCO site last night, particularly (but not exclusively) those related to Unit 4. There are several reports of foreign objects falling into the SFP or being found in the stored fuel assemblies over the years (bolts, washers, metal shavings, etc.), and the more recent reports mention that they are continuing strict countermeasures against foreign object introduction that were adopted a few years ago. The only enumeration I found of what those countermeasures consists of was basically different ways of saying, "we'll be more careful," and no mention was made of plastic covers being adopted on a regular basis. In fact the locations of where some of the foreign objects were found inside the fuel assemblies suggest that they are not using plastic covers on a regular basis. I also see no mention of plastic covers in the list of things to be done in the maintenance period that was underway when the earthquake hit.

So, not much support so far for the possibility of plastic covers being in place in SFP4.
Maybe the covers were a special-case for the MOX study after all?

 

[Astronuc]

Would a fast-neutron chain reaction in the plutonium be absolutely excluded?

Fast reactors use a tight fuel lattice configuration and 20% fissile inventory. LWRs have a maximum of 5%, and TEPCO probably uses 4% or less, based on annual cycles and between 1/4 and 1/3 core batch sizes. The spent fuel is even lower enrichment because of depletion of fissile inventory. So no fast-neutron chain reaction.

 

[Astronuc]

Further follow-up (context: cphoenix's superheated steam explosion theory):


I skimmed through a bunch of past press releases on the TEPCO site last night, particularly (but not exclusively) those related to Unit 4. There are several reports of foreign objects falling into the SFP or being found in the stored fuel assemblies over the years (bolts, washers, metal shavings, etc.), and the more recent reports mention that they are continuing strict countermeasures against foreign object introduction that were adopted a few years ago. The only enumeration I found of what those countermeasures consists of was basically different ways of saying, "we'll be more careful," and no mention was made of plastic covers being adopted on a regular basis. In fact the locations of where some of the foreign objects were found inside the fuel assemblies suggest that they are not using plastic covers on a regular basis. I also see no mention of plastic covers in the list of things to be done in the maintenance period that was underway when the earthquake hit.

So, not much support so far for the possibility of plastic covers being in place in SFP4.
Maybe the covers were a special-case for the MOX study after all?

All utilities are concerned with 'foreign materials' on nuclear fuel, and all have a 'foreign materials exclusion' program - at least they should by now. Failure due to 'debris' has been a significant issue in the 1980s through 1990s. Debris-resistant features were added to the fuel, but more importantly, utilities implement programs to prevent contamination of fuel. Foreign materials do not belong in the fuel or the core.

Fresh fuel arrives at the plant in containers, and there is usually a plastic cover. MOX fuel in which the MOX is derived from reprocessed spent fuel has more radioactivity than conventional UO2, so it is protected more so. The plastic covers are there to protect the fuel and to some extent protect the workers. However, the plastic covers are normally removed when the fuel is placed under water. On the other hand, I am not familiar with TEPCO practices or procedures, or the context of plastic covers in conjunction with fuel in Unit 4. Unit 4 did have a large batch of fresh fuel, but Unit 3 had MOX fuel - and only 32 assemblies of MOX.

 

[densha_otoko]

Smoke from 4 (maybe 3) on the increase this morning. Most I have seen in April, yet it might just be the first calm wind day in weeks. http://www.tepco.co.jp/nu/f1-np/camera/index-j.html.

 

[MiceAndMen]

I see the international nuclear industrial complex colluding with them. The Swedish nuclear authority says that the French regulator was out of line to regard Fukushima as an INES level 6 accident when the Japanese said 4 (or later 5).

It needs a British professor Busby to produce alarming graphs of uranium spreading out over the Pacific from tabular EPA data. The EPA that does not want to monitor the radioactivity in fish.

The IAEA (with its Japanese boss) is completely passive.

IAEA is a completely toothless tiger according to some reports I've seen. No surprise there. I'm more concerned about China and the Koreas, especially if the plant is still chuffing out radioactivity when typhoon season gets going.

 

[MadderDoc]

Mm, something's going wrong there. See webcam image 28/4 08:00 AM (Japan Time)

http://www.tepco.co.jp/nu/f1-np/camera/index-j.html

Yes, the position of this plume at 08:00 is a bit unusual. It looks to me as if it is coming from no 1? That's rare. In the current webcam at 09:00 however, it appears SFP4 has now started steaming, so no longer easy to discern what's going on behind that. Cache of older than current webcam is held at: http://gyldengrisgaard.dk/tepcowebcam/

 

[sp2]

If you don't mind my asking, how the hell did they clean that up?

That sounds like a big-deal accident.

In the core at power, the radiation field is so very different than simple radionuclide decay. The thermal and fast neutron fluxes are on the order of 10¹⁴ n/cm²-s. And the gamma and beta radiation is intense.

About 20 years ago, I was involved as a consultant to a utility where they managed to break a fuel rod outside of the core. It had failed during the cycle, and they managed to break it while moving the assembly during the refueling outage. The fuel rod was not discovered until they were draining the cavity above the RPV, and the radiation alarms went off. The operators stopped, reflooded the cavity and went to take a look.

The fuel rod was broken in 4 pieces. The top and bottom sections were about 2 ft each, and there were two 5-ft sections. One section was empty of fuel! It's activity was about 5000 R/hr, IIRC. Another section was about 2000 R/hr. I'd have to dig up my notes - but they were hot. The NRC wanted to know - where did 1 kg of UO2 go!? Well the answer was - it was distributed in the primary system as fuel particles and uranyl ions. The Np-239 in the reactor coolant (as well as increased Xe, Kr, I and Cs) was a really good indication that they had a degraded failure in the core. They just didn't bother to go look for it during the outage.

The senior plant management were fired.

 

[Danuta]

Many countries experiment with this. So it must be safe.

LOL. I know you didn't mean this the way I read it.

 

[UNECCS]

2. they ADD the core-damage values of drywell and wetwell. i simply don't understand the logic behind that. shouldn't both methods give the SAME result?

I have same question.
I think reason is Goodness of TEPCO's hart.

 

[Astronuc]

If you don't mind my asking, how the hell did they clean that up?

That sounds like a big-deal accident.

It wasn't a big accident. But it was serious because the fuel rod broke outside of the reactor vessel.

They carefully picked up the pieces of broken fuel rod and put them in the appropriate container. About half the fuel had washed out and ended up dispersed in the primary system. It would mostly be caught on filters. It costs a utility big bucks to disposed of those filters, hence utilities really don't want fuel failures - not even one - for an economic standpoint and from a safety standpoint.

PWRs are actually capable of handling hundreds of failed rods, but no one would ever want to have to deal with that. In the last 20 years, even one failure causes alarm at a NPP.

As of Jan 1, 2011, the US has adopted a zero fuel failure policy. It has been an industry objective for the last two decades.

 

[MiceAndMen]

If you don't mind my asking, how the hell did they clean that up?

That sounds like a big-deal accident.

In 2004 it was revealed that the Vermont Yankee plant had lost track of some fuel rod pieces. They were last seen in 1979. A couple of years before that, the operators of the Millstone I plant lost 2 fuel rods completely. They are reasonably sure they know what happened to them, but can't prove it.

http://www.vpr.net/news_detail/71411/

There have been other cases, too. In the United States incidents such as this most definitely become federal cases.

 

[MadderDoc]

This is from the evening of April 1. Play 00:42 to 00:45 and you'll see the glow in the dark spot. http://www.youtube.com/watch?v=CtgRBpgbZww&feature=related. I believe it's been visible on a few other occasions. Is that the SW corner of #4?

Yes, more precisely the position of that light is the upper half of the remaining top wall panel on the south wall of unit 4. Tepco has installed powerful lamps in the area, so I think it more likely is a reflection of light from those that we see in that video, than Cherenkov light coming from the sfp.

 

[Astronuc]

In 2004 it was revealed that the Vermont Yankee plant had lost track of some fuel rod pieces. They were last seen in 1979. A couple of years before that, the operators of the Millstone I plant lost 2 fuel rods completely. They are reasonably sure they know what happened to them, but can't prove it.

http://www.vpr.net/news_detail/71411/

In the United States incidents such as this most definitely become federal cases.

I've been involved in similar situations where we reconstructed a fuel rod or two from various broken pieces, and records.

For older units like VY, Millstone-1 and Pilgrim, it can be a royal pain for complete accountability. VY, and I believe Pilgrim, had some problems with CILC failures in the 1970s. Millstone-1 may have had similar problems. I remember reading some horrendous off-gas activities.

 

[sp2]

Thanks.

So, forgive me for another stupid question, but does that mean somebody's absorbing 20 or 50 Sv/hr for a while (or anything close to that), somewhere in that clean-up process?
(I assume not, since they'd probably be dead?)

Also, what's the 'zero-tolerance policy' mean? Just that these incidents have to be reported now?

It wasn't a big accident. But it was serious because the fuel rod broke outside of the reactor vessel.

They carefully picked up the pieces of broken fuel rod and put them in the appropriate container. About half the fuel had washed out and ended up dispersed in the primary system. It would mostly be caught on filters. It costs a utility big bucks to disposed of those filters, hence utilities really don't want fuel failures - not even one - for an economic standpoint and from a safety standpoint.

PWRs are actually capable of handling hundreds of failed rods, but no one would ever want to have to deal with that. In the last 20 years, even one failure causes alarm at a NPP.

As of Jan 1, 2011, the US has adopted a zero fuel failure policy. It has been an industry objective for the last two decades.

 

[NUCENG]

I believe there is washout and dissolution of the fuel, but not nessarily melting - particularly if there was water in the bottom third of the cores. The question is - was there water in the bottom third of the cores?

This event seems to exceed the predictions of the LOCA and Arrested Core Melt scenario which is the design basis for radiological consequences for plant licensing. The scenario of a total loss of AC (Station Blackout) and Loss of decay heat removal after battery failure are way beyond design basis space. The complete loss of Secondary Containment is beyond design basis. Spent fuel pool fires, and hydrogen explosions have been postulated and studied, but never to the extent of four plants on the same site.

But so far the consequences are not very far from predictions for the design basis accident. Evacuations have helped. But even employees and contractors on site are still within emergency dose limits. The reactors are write-offs, Dislocation and compensation of evacuees will be expensive. Impact of the loss of power production and expense of replacing that generation will affect the economy for a while. Japan which is short of space for its population will be more crowded. Long term health impacts will probably have to be estimated because they may not be statistically detectable. I hesitate to say no radiation induced early deaths, because I agree that the accident may be responsible for traumas and suicides as well. But this accident could have been, and still could become, so much worse.

 

[dh87]

About explosions, I am not expert, I write only on base of observations: #1 explosion, big pressure in reactor building from venting then small, centered hydrogen explosion. #3 explosion, yest we can see it on video, first fireball from SFP location, then big explosion going up, but I don't think that it was from recriticality in SFP, I think that first explosion in SFP damaged drywell and reactor vessel so there was big release of pressure and maybe hydrogen explosion. If there would be so big explosion from SFP then there would be more very hight radioactive pieces of fuel rods, but they found only 300 and 900 mSv/h mayby from reactor cap... Also the big "up" explosion appear to be from center of building/core location not from sfp like fireball...

I claim to know less about explosions than you, but I had been thinking about the #3 explosion the same way as you for exactly the reasons you cite. The trouble with this explanation is that the reported pressures in the primary containment vessel don't seem to be changed by the explosion. In contrast, in #2 the pressures fall sharply after the explosion apparently blows a hole in the containment.

 

[Astronuc]

This event seems to exceed the predictions of the LOCA and Arrested Core Melt scenario which is the design basis for radiological consequences for plant licensing. The scenario of a total loss of AC (Station Blackout) and Loss of decay heat removal after battery failure are way beyond design basis space. The complete loss of Secondary Containment is beyond design basis. Spent fuel pool fires, and hydrogen explosions have been postulated and studied, but never to the extent of four plants on the same site.

But so far the consequences are not very far from predictions for the design basis accident. Evacuations have helped. But even employees and contractors on site are still within emergency dose limits. The reactors are write-offs, Dislocation and compensation of evacuees will be expensive. Impact of the loss of power production and expense of replacing that generation will affect the economy for a while. Japan which is short of space for its population will be more crowded. Long term health impacts will probably have to be estimated because they may not be statistically detectable. I hesitate to say no radiation induced early deaths, because I agree that the accident may be responsible for traumas and suicides as well. But this accident could have been, and still could become, so much worse.

I believe the DBE/DBAs assume core coolability is re-established pretty quickly using available systems. I don't think DBAs assume the ECCS and EDGs (emergency power) is completely gone.

This event is an entirely different chapter. It is a textbook example of what to avoid.

 

[Nullpunkt]

About explosions, I am not expert, I write only on base of observations: #1 explosion, big pressure in reactor building from venting then small, centered hydrogen explosion. #3 explosion, yest we can see it on video, first fireball from SFP location, then big explosion going up, but I don't think that it was from recriticality in SFP, I think that first explosion in SFP damaged drywell and reactor vessel so there was big release of pressure and maybe hydrogen explosion. If there would be so big explosion from SFP then there would be more very hight radioactive pieces of fuel rods, but they found only 300 and 900 mSv/h mayby from reactor cap... Also the big "up" explosion appear to be from center of building/core location not from sfp like fireball...

Nice side by side video on youtube of #1 and #3 explosion

http://www.youtube.com/watch?v=1Q3ljfLvHww"

Very impressive to see the difference in shape and power.

If you look at the frame by frame version of #3 explosion,
you can clearly see the fireball, followed by the implosion and catapult shot.

http://www.youtube.com/watch?v=9PHQ3IJHJbw"

It seems to me, that the implosion/explosion also has impact on structure of building #4.
Could be the reason for the curved damage seen on the left side of the building #4, after it blow up.

 

[MiceAndMen]

Assume a spent fuel assembly with no damage to any fuel rods was lifted completely up and out of its SFP, swung through the open air for a minute or two, and lowered into another pool at ground level. Is that feasible at all?

Every day those SFPs are left sitting there 30 meters off the ground supported by weakened concrete shells is another day waiting for something really bad to happen. If one could jury-rig a closed-loop cooling system for each SFP then it could buy some time, but even that assumes the pools are not leaking. And what if they are leaking? Their current feed and bleed strategy can't go on much longer. It boggles the mind to think that they might actually believe they can get out ahead of this thing with tonnes of contaminated water continuing to accumulate day in and day out.

 

[Jim Lagerfeld]

Hi Guys, keep up the fantastic work. This thread has keep me riveted for weeks!

I'd usually lurk but I would dearly like to hear you opinion on this.

Yesterday NHK reported that TEPCO had finally admitted a leak in spent fuel pool number 4 was likely.

TEPCO: Water may be leaking from No. 4 reactor fuel pool
http://www3.nhk.or.jp/daily/english/27_09.html

Today they have retracted:

TEPCO: Water isn't leaking from No. 4 reactor pool
http://www3.nhk.or.jp/daily/english/28_05.html

 

[Azby]

And its not the first time he has made this mistake in a video. I first heard about the report in question via one of his videos weeks ago, and in that video I believe he used the phrase 'several miles'. I was already miffed with his iffy analysis of the unit 4 pool video, so I thought I better check the original source detail, and sure enough it said 1 mile not several miles.

I also note in this latest video that he is sloppy when describing the dimensions of the fuel pool.

I appreciate that members of this forum are wiling to consider all possibilities. It's open minded and good science. But I have serious questions about Gunderson's credibility, as well as Busby's. The latter's arguments concerning radiation epidemiology, his ecological studies of Sellafield, and his "Second Event Theory" of DNA mutation have been pretty well demolished more than once. The report of the CERRIE committee from 2004 makes very informative reading in this regard. It notes that as far as Busby's claims are concerned, "The Committee concluded that the available scientific evidence did not support these hypotheses and, in many cases, substantially contradicted them." He threw a fit. Time and again during committee, one of which he chaired, he was asked to provide the papers upon which he based various claims so the others could review them, and was unable to. Sloppy does not begin to describe it. He makes this stuff up.

http://www.cerrie.org/report/

(For the record, I've been lurking for a while and just signed on. I'm not a scientist, but direct a design theory lab in Tokyo, doing mainly environmental design studies as well as a long-term collaboration with a neuroscience team on hand-brain issues. I'm learning a lot here. My hats off to you all)

 

[MiceAndMen]

Hi Guys, keep up the fantastic work. This thread has keep me riveted for weeks!

I'd usually lurk but I would dearly like to hear you opinion on this.

Yesterday NHK reported that TEPCO had finally admitted a leak in spent fuel pool number 4 was likely.

TEPCO: Water may be leaking from No. 4 reactor fuel pool
http://www3.nhk.or.jp/daily/english/27_09.html

Today they have retracted:

TEPCO: Water isn't leaking from No. 4 reactor pool
http://www3.nhk.or.jp/daily/english/28_05.html

I honestly don't think they know what they're doing, have a fraudulent "plan" to deal with the cleanup going forward, and cannot be trusted to tell the truth about anything. They cannot deny what others see in photographs or measure with monitoring devices. All else is spin at this point.

 

[Wrothamis]

Is it safe to go to Japan now? Will the nuclear plants get worse or is it 100% under control now? Thanks.

 

[TCups]

The fuel in the SFP is 'spent', in addition to the fact that is started with low enrichment. The available reactivity is low because it is 'spent'. The rate a which positive reactivity could be inserted is relatively low, so a prompt critical event is unlikely. Coming out of a subcritical configuration with a very low neutron source, rather than starting at a critical configuration, I don't believe the configuration in the SFP supports prompt supercritical.

The explosions at Units 1 and 3 occurred well before the pools would have dried out, and it is more likely the hydrogen came from oxidation of the cladding in the cores.

I don't see the explosions being nuclear.

If the pools had dried out, there certainly wouldn't be any moderator to allow criticality. If there was water covering the fuel at the time of the explosion, the pressure in the pool would have been more of an increase in hydrstatic pressure, and that would crush the fuel into a more critical configuration.

Re-criticality would have been a concern AFTER the hydrogen explosions, when they TEPCO was reintroducing water into the SFPs. However, I would have expected them to borate that water.

All I see are chemical (H₂+O₂) explosions, not nuclear.

OK, thanks Astronuc. Then, at least in my opinion, having not been convinced otherwise by any hard data or inconsistency in the photographic or video evidence, I am still clinging to the sequence I had first hypothesized: 1) hydrogen explosion in the drywell containment of RPV3, 2) directed venting of the explosion into the upper SFP3 via the fuel transfer chute (and also into the torus), 3) secondary explosion of the hydrogen in the upper floor of Bldg 3 (also from hydrogen originating from the reactor core of Unit 3 and probably not SFP3 damaged fuel), and, almost simultaneously, 4) hot water vaporization/steam explosion mushrooming vertically from the SFP3.

I am not perhaps as sure as you about the time frame of when the SFP3 might have gone dry (not because I doubt you, but because I haven't done the math), but I am fairly sure that mushroom effect is steam, and that the origin of the steam must have been water in the SFP, and that is consistent with your assessment of water still in the SFP3. The shock wave --> hydrostatic wave --> mechanical damage to spent fuel racks would be a reasonable explanation of why some fragments of damaged fuel rods may have been carried aloft by the steam explosion, extraction of a fuel rod assembly by a "ballistic" FHM's mast now seeming to be most unlikely.

No one seems to have found an alternate "authentic" sound track other than the 3-Boom soundtrack of the Bldg 3 explosion, either. . .

Addendum: BTW, I doubt implosion of Bldg 3 occurred. I think the video shows explosion with a shadow of the cloud of exploding gas darkening the upper portion of the building. I can't imagine any physical process that could possibly have occurred to "implode" the upper portion of Bldg 3.

 

[etudiant]

There have been decades of collusion between the nuclear industry, regulators, and the media in Japan. There are ample reasons having nothing to do with mass panic for them to want to withold information.

http://www.bloomberg.com/news/2011-03-17/japan-s-nuclear-disaster-caps-decades-of-faked-safety-reports-accidents.html

People are fired from their jobs if they dare to question the official company line.

http://japanfocus.org/-Makiko-Segawa/3516



Wow. They are certainly under tremendous pressure from many sides. I do not agree that their culture absolves irresponsible actions on their part in the name of some "path of least harm". If shame is necessary then it needs to be felt, and strongly, by those responsible. They should be shamed where appropriate. They NEED to be shamed where appropriate.

http://www.nytimes.com/2011/04/27/world/asia/27collusion.html?_r=1&hpw=&pagewanted=all

Does anyone think TEPCO's plan to remediate the situation over the next 3, 6 and 9 months is realistic? They barely got off of square one and found their plan to fill Unit 1's containment with water may be compromised by a leak. They are only now coming to the realization that Unit 4's SFP is probably leaking.

Here is what Japanese leaders have to fear: that at some point an international consensus develops that they are no longer capable of managing the ongoing problems on their own. At some point, perhaps, the international community may find it desirable to take away the keys to the car, so to speak, and TELL them how to proceed with the cleanup.

Patience does not last forever, and Japans's political and industrial institutions are well aware of that. The longer they are able to prolong a "fog of war" type atmosphere surrounding this fiasco, the longer they can put off their day of reckoning.

This is over the top, imho.
Does anyone have either the record or the competencies to assume entitlement to judge?
Japan is the very first victim of this disaster and they are certainly in constant communication with the world's nuclear community to get the best available counsel.
This situation is a mess exacerbated by the disaster that generated the problem and also hid its gravity during the crucial early days. At this point, with the plant flooded 20 feet deep by highly radioactive effluent, we are all in an unprecedented situation. No one knows what to do.
TEPCOs approach, going slow, building water treatment plants and cleaning up the site may be right or entirely wrong. With 500 people on site, versus the usual 5000, they are clearly biding their time.

Of course, maybe the only way to avoid a much greater problem is to throw people at it. However, unless someone has a plausible plan that shows real benefits, it is unreasonable to push for an acceleration, because the human cost would rise dramatically.

 

[MadderDoc]

I'm not so sure about the hydrogen explosion. Wikipedia states that nobody is sure what caused the big explosion. There's only the fact that the reactor went to 30 GWt and then KABOOM.
I don't think that a hydrogen explosion is very likely. I'm not a chemist, but a hydrogen explosion would mean, that the reactor must have generated enough hydrogen to destroy the building and lift the 1000 ton heavy reactor cap upwards in just a few seconds <..>

I think the first fraction of a second of the blast did represent an initial hydrogen explosion, which blew away, crucially, the west wall support for the overhead crane, so that the two heavy booms and the crane itself fell on top of the reactor lid.

We know from overfly videos that the northern boom indeed has sunk partly into the service floor, and in that process has completely devastated the concrete deck at the west end where it fell. The fallen overhead crane has fallen on top of something, at the very least it must have its hook etc uderneath it, and those things must have pressed powerfully into the reactor lid. I think this hit from the overhead crane triggered something akin to a BLEVE (a boiling liquid expanding vapour explosion) from the area of the lid or from the area close to the SFP chute. A BLEVE can be extremely powerful, and it will produce a high buoyancy airmass (1 m³ of hot water flashed to vapor has a lifting power of about 1000 kg). A bleve will splash a lot of hot liquid water around too.

It is a somewhat overseen fact that the explosion of unit 3 really produced a lot of steam, quite unlike unit 1, and not only in the shape of a mushrooming cloud, but also coming from ground level from water apparently splashed as far as to unit 1 (counter to the wind direction!) , also a lot from the area around unit 4. Indeed the satellite photo taken 3 minutes after the explosion strongly suggest there's water on the roof of turbine building 4. As if it had just rained.

I may well be wrong about several things in this scenario, but whatever the exact chain of events may have been, I think the character of the explosion at unit 3 becomes inexplicable unless we assume that it in some way involved the expulsion of large amounts of hot water under pressure. It certainly was not (just) a hydrogen explosion.

 

[MiceAndMen]

This is over the top, imho.

You are entitled to your opinion, as I am to mine.

Does anyone have either the record or the competencies to assume entitlement to judge?

Yesterday they said SFP was leaking. Today they say it is not. QED

One does not have to be a good actor to recognize a bad one.

 

[dh87]

OK, thanks Astronuc. Then, at least in my opinion, having not been convinced otherwise by any hard data or inconsistency in the photographic or video evidence, I am still clinging to the sequence I had first hypothesized: 1) hydrogen explosion in the drywell containment of RPV3, 2) directed venting of the explosion into the upper SFP3 via the fuel transfer chute (and also into the torus), 3) secondary explosion of the hydrogen in the upper floor of Bldg 3 (also from hydrogen originating from the reactor core of Unit 3 and probably not SFP3 damaged fuel), and, almost simultaneously, 4) hot water vaporization/steam explosion mushrooming vertically from the SFP3.

What is the source of the oxygen for a hydrogen explosion in the dry well?

 

[Danuta]

This situation is a mess exacerbated by the disaster that generated the problem ...

It was more like a problem waiting for a disaster, than a disaster that generated the problem. "Sitting duck" comes to mind, especially when thinking in terms of recorded seismic activity and tsunami maximums.

 

[Curium]

Explosion of Fukushima Unit 3 (Spent Fuel Pool?)

Hello! Have a question about one aspect of the Fukushima disaster which is still a topic of contention: etiology of the explosion of Unit 3.

Based on what I have read here and elsewhere, the theory which makes most sense to me is

- Loss of power in the tsunami shut down the cooling pumps, Spent Fuel Pool Three (SFP3) heated up to the point that it boiled off the water that it contained, exposing fuel rods
- Zircalloy cladding overheated and evolved hydrogen
- The building imploded before it exploded. Looking at the video frame-by-frame, the white/blue exoskeleton of the building collapses inward before the orange flash of the detonation
- This was an oxyhydrogen implosion caused when the air/fuel mixture reached conditions ripe for it to ignite
- A small fraction of a second later, the orange flash appears, its initial location, size, and vertical shape are consistent with the SFP3 burning/exploding

Now, for the real question: is it physically possible for the implosion to have caused a criticality in the SFP3? If not, why not? If so, how?
I can imagine the already-damaged fuel rods being forced together, in a manner similar to the way in which shaped charges are used to implode the core of nuclear weapons, which causes the criticality, and increases the yield of the explosion.

But, is this plausible based on the kinetics of what we see happened in the building, and based on the composition of the nuclear fuel that was in the SFP? I heard that some of the fuel in SFP3 was not "spent" rods but actually fresh rods of MOX fuel, which would be radioactively "hotter" than spent fuel. Not sure if that makes any difference.

I did study some advanced physics courses at university but nothing thereafter, so can the experts reduce this question to the quasi-layman level? Then I can follow this better as more details emerge.

My sincere thanks,

Curious Curium

 

[TCups]

What is the source of the oxygen for a hydrogen explosion in the dry well?

I think that was hashed out and explained by others smarter than me back somewhere around post #600-800 or so.

 

[dh87]

I think that was hashed out and explained by others smarter than me back somewhere around post #600-800 or so.

I thought that you might know, since you propounded a theory. In elektrownik's theory, the oxygen for the initial hydrogen explosion is in the building above the SFP. Then, the second fireball occurs above the building after the hydrogen released from the primary containment vessel has a chance to mix with atmospheric oxygen.