Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[Dmytry]

theres water in drywell now, and there was that feed and bleed stuff, so those core damage assessments from the CAMS readings are probably utter nonsense.

 

[Samy24]

I don't think that's his question. In the pdf he posted there are two assessments: Core damge (drywell) and Core damage (wetwell) for all reactors.
But core damage inside the dry- and wetwell is imho pointless - that's not damage anymore, but molten corium... or am I misunderstanding something?

Drywell = Inner containment, hull around the RPV
Wetwell = Torus, condension chamber

OK I found the link:
http://www-pub.iaea.org/MTCD/publications/PDF/te_955_prn.pdf"
Page 53 for the readings in dry-well
Page 54 for the readings in wet-well

The document only references to readings 1 hour and 24 hour after the shutdown. The report from TEPCO is over 72 hours after the shutdown. Maybe someone with knowledge can transform the values from 24 to 72 hours after shutdown? Should be lower ;)

>100 Sv/h 72 hours after shutdown "could" indicate a partial melt through?

 

[Samy24]

theres water in drywell now, and there was that feed and bleed stuff, so those core damage assessments from the CAMS readings are probably utter nonsense.

Are there reports that 72 hours after the shutdown the dry-well of unit 1-3 was flooded?

 

[SteveElbows]

That's quite different from "fuel found 2 miles away". Blegh.

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.

 

[Dmytry]

Are there reports that 72 hours after the shutdown the dry-well of unit 1-3 was flooded?

Hmm. They're using 72 hours after shutdown readings for the core damage evaluation?

 

[Samy24]

Hmm. They're using 72 hours after shutdown readings for the core damage evaluation?

Yes, on their website:
http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110427e18.pdf"

 

[SteveElbows]

Two robots sent into the reactor No. 1 building at the plant yesterday took readings as high as 1,120 millisierverts of radiation per hour.

http://www.bloomberg.com/news/2011-04-27/tokyo-water-radiation-falls-to-zero-for-first-time-since-crisis.html

I hate the sort of headlines such stories generate, talking about 'rising levels'. Without knowing whether the robot(s) visited exactly the same locations at reactor 1 as they did on their first visit, we don't know if anything has risen, or whether the robots just stumbled upon a more contaminated area this time.

Either way its not a good number, but numbers even higher than this would not surprise me as they slowly explore further.

These sorts of numbers are also a reason not to stretch the complaints of PR and coverups too far. In theory there may be plenty we are not being told but they have also released plenty of info that was not good news by any stretch of the imagination. The explosions somewhat reduced the temptation to do a complete and utter coverup, and although I am not overjoyed with the quality of data that is available to us, its a lot more than I might have imagined we would get.

 

[elektrownik]

I hate the sort of headlines such stories generate, talking about 'rising levels'...

There was article on nhk about this, radiation was from small water leak, and also there was information that tepco think that some water leak from reactor core or drywell via pipes

 

[ascot317]

I hate the sort of headlines such stories generate, talking about 'rising levels'. Without knowing whether the robot(s) visited exactly the same locations at reactor 1 as they did on their first visit, we don't know if anything has risen, or whether the robots just stumbled upon a more contaminated area this time.

That NYT article is comparing it to measurements of 400mSv/h or the piece of debris with 900mSv/h. That radiation at the outside is something quite different to radiation inside a containment structure is what they don't understand. This article suggests that the situation is going worse due to these numbers. Which is false in itself.

Either way its not a good number, but numbers even higher than this would not surprise me as they slowly explore further.

These sorts of numbers are also a reason not to stretch the complaints of PR and coverups too far. In theory there may be plenty we are not being told but they have also released plenty of info that was not good news by any stretch of the imagination. The explosions somewhat reduced the temptation to do a complete and utter coverup, and although I am not overjoyed with the quality of data that is available to us, its a lot more than I might have imagined we would get.

Inside the reactor structures we already see higher levels of radiation, which is not a surprise, of course.

We're not in the 80ies or 90ies anymore, making information available to masses is the easiest thing to do. In this situation, there's absolutely no reason to withhold information. We're beyond the stage of possible mass panic.

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.

Watching his videos a light bulb in my head starts blinking ("crank" written over it). He might be qualified and all, but he's mixing up his facts a little too much. Doesn't go well with a name tag with "nuclear engineer" written on it.

 

[PietKuip]

I don't think that's his question. In the pdf he posted there are two assessments: Core damge (drywell) and Core damage (wetwell) for all reactors.
But core damage inside the dry- and wetwell is imho pointless - that's not damage anymore, but molten corium... or am I misunderstanding something?

"Damage" was a highly misleading euphemism. That is what I come to understand now.

 

[Bandit127]

Perhaps I should ask a clearer question. From the http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110427e18.pdf", can we assume that approximately 45% of the core of Unit 1 (for example) is now in the Drywell?

If not, please could someone explain how we should interpret this data?

 

[Samy24]

Perhaps I should ask a clearer question? From the http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110427e18.pdf", can we assume that 45% of the core of Unit 1 (for example) is now in the Drywell?

If not, please could someone explain how we should interpret this data?

I'm not even a physicist student. Learned only from this thread.

But if I understand the book correctly even a small damage to the fuel can be detected by the CAMS readings. Depending on the amount of radiation in the dry-well and the wet-well the extensive of the damage can be estimated.

The core need not but could be in the dry-well to read high radiation in the dry-well!

 

[PietKuip]

Watching his videos a light bulb in my head starts blinking ("crank" written over it). He might be qualified and all, but he's mixing up his facts a little too much. Doesn't go well with a name tag with "nuclear engineer" written on it.

The issue is whether his theory that a chemical (or steam) explosion triggered a prompt criticality is plausible.

Some people here should know whether it is likely or absolutely impossible. Even if it is remotely improbable, spent fuel pools all over the world are much more dangerous than I ever had imagined them to be. It means that atomic explosions are possible almost anywhere.

Suppose a terrorist shooting a missile into an SPF, just to make a dirty bomb. But could that trigger prompt criticality, and amplify the explosive effect of the missile to make a mushroom cloud?

Surely this kind of scenarios must have been analyzed somewhere?

 

[Bandit127]

I'm not even a physicist student. Learned only from this thread.

But if I understand the book correctly even a small damage to the fuel can be detected by the CAMS readings. Depending on the amount of radiation in the dry-well and the wet-well the extensive of the damage can be estimated.

The core must not be in the dry-well to read high radiation in the dry-well!

So, the CAMS readings just give a prediction of the fuel damage if I understand you correctly. And that all the fuel could all still be in the RPV and we could still have these predictions?

If that is so, the radiation readings from the Drywell simply predict that approximately 45% of the fuel is damaged in Unit 1. But the Wetwell predicts that approximately 10% of the fuel is damaged.

If so, there is a big difference between the predictions. And TEPCO adding the two together doesn't make sense.

Adding the two only seems to make sense if it is predicting the distribution of the damaged fuel.

We know TEPCO are learning fast and could well have made a mistake to add the two together...

 

[NUCENG]

I don't think that's his question. In the pdf he posted there are two assessments: Core damge (drywell) and Core damage (wetwell) for all reactors.
But core damage inside the dry- and wetwell is imho pointless - that's not damage anymore, but molten corium... or am I misunderstanding something?

Drywell = Inner containment, hull around the RPV
Wetwell = Torus, condension chamber

If they used something similar to the IAEA standard for estimating core damage those numbers mean the percentage of total core source term that has been released to the drywell and wetwell. They don't say that they estimate here how much has been released from containment or the suppression chamber. They may be estimating that from environmental monitoring. Nor does this say what is left inside the RPV. If we had one of these two numbers we could estimate the other. It may be used to estimate the transport and hazard to the public offsite using meteorological modeling. It is educated guesswork. The dose rate at any specific work location and whether it is airborne, or fixed or loose or in pools is much more immediately important.

 

[PietKuip]

Adding the two only seems to make sense if it is predicting the distribution of the damaged fuel.

We know TEPCO are learning fast and could well have made a mistake to add the two together...

This is version 2.0 of the .pdf file. Let us assume they did it right.

 

[bytepirate]

I'm not even a physicist student. Learned only from this thread.

But if I understand the book correctly even a small damage to the fuel can be detected by the CAMS readings. Depending on the amount of radiation in the dry-well and the wet-well the extensive of the damage can be estimated.

The core need not but could be in the dry-well to read high radiation in the dry-well!

i am a bit puzzled...

1. the estimation of core damage by CAMS readings is highly unreliable:
'Containment monitor readings indicate the minimum level of core damage. Low containment
radiation readings do not guarantee that the core is undamaged. Actual containment radiation
monitors may provide inconsistent readings or may underestimate the level of core damage because
the release from the core may by-pass the containment, may be retained in the primary system, may
be released over a long period of time, may not be uniformly mixed in the containment atmosphere,
or the mixture may be different than assumed in developing this procedure.' (from http://www-pub.iaea.org/MTCD/publications/PDF/te_955_prn.pdf)

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?

3. they use ONE value, that they say they have recorded 97h after SCRAM (unit 1).
this value has never been released to the public before.
if i put the earliest released readings in their diagram, i get 100% damage...
i have not checked for the other units.

4. how long was the core partially uncovered without cooling? is it reasonable, that the core damage is below 100% after this time?

i would really appreciate, if someone with a deeper knowledge than me, could comment on this.

 

[Samy24]

The issue is whether his theory that a chemical (or steam) explosion triggered a prompt criticality is plausible.

Some people here should know whether it is likely or absolutely impossible. Even if it is remotely improbable, spent fuel pools all over the world are much more dangerous than I ever had imagined them to be. It means that atomic explosions are possible almost anywhere.

Suppose a terrorist shooting a missile into an SPF, just to make a dirty bomb. But could that trigger prompt criticality, and amplify the explosive effect of the missile to make a mushroom cloud?

Surely this kind of scenarios must have been analyzed somewhere?

A nuke is also triggered by a conventional explosion. Designed very efficent but complex with only a small amount of uranium or plutonium.

No one does experiments with tons of fuel even if not highly enriched.

Some people belief that the explosion energy in Chernobyl was a result of fission.

Tests with faulty designed (bad chain reaction) nukes show that also a small explosion with only the energy of 100 tons TNT is possible.

 

[ascot317]

Tests with faulty designed (bad chain reaction) nukes show that also a small explosion with only the energy of 100 tons TNT is possible.

A fizzle from spent fuel? Hm.

It's quite hard to even produce a fizzle.

 

[NUCENG]

Perhaps I should ask a clearer question. From the http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110427e18.pdf", can we assume that approximately 45% of the core of Unit 1 (for example) is now in the Drywell?

If not, please could someone explain how we should interpret this data?

No I posted a link to a copy of NUREG-1465 quite a while back. This document gives an brief description of severe accidents broken down into 4 stages. The first is Gap release due to perforation of fuel cladding. The scond is called the early in Vessel release and comes from melting fuel. There may or may not be an RPV to enter the Ex-Core phase. Finally there is a small in-vessel release late in the accident from remaining fuel inside the RPV. These are gross estimations. An accident may have significant fuel melting in vessel without corium being released to the drywell. The drywell and wetwell sources come from operation or SRVs early in the accident or from piping leaks in the drywell that can overflow the Vent Pipes into the suppression pool. The estimates being made by TEPCO are based on experiments with fuel failures and test assemblies and actual data from Chernobyl and TMI2.

There may be 45% of the Noble Gasses, Halogens released from the core in the vessel that are now in the drywell Maybe a few percent of actinides, heavy alements and metal fission products have also been released. If the vessel has been breached a lot of the core may still be inside the vessel oozing around like volcanic lava, but even that is mre science fiction than probability.

 

[clancy688]

those numbers mean the percentage of total core source term

So, let's take the following example for dummies like me:

Let's guess there's an RPV with only one fuel rod. Now there have been severe cooling problems. The fuel rod was uncovered for a short amount of time and has oxidated and ruptured. We don't know if it indeed has molten.
But because of the constant cooling, fission products such as iodine, cesium, cobalt, strontium etc. have been washed out and are now somewhere in the RPV, the dry- and wetwell.
CAMS is now measuring extremely high radiation, indicating that 30% of the radiating inventory is somewhere in the drywell and 5% somewhere in the wetwell.
Overall it doesn't necessarily mean that the fuel has molten. It's only indicating, that the fuel cladding ruptured and fission products can escape from the fuel rods?

Back to Fukushima: So 55% of Unit 1s core inventory of fission products is not contained by the fuel rods anymore but swimming in the cooling water? But there's NOT 55% of the core gone, like molten down? Or at least, those numbers do not indicate or show whether or how much of the core has molten?

 

[Samy24]

i am a bit puzzled...

1. the estimation of core damage by CAMS readings is highly unreliable:
'Containment monitor readings indicate the minimum level of core damage. Low containment
radiation readings do not guarantee that the core is undamaged. Actual containment radiation
monitors may provide inconsistent readings or may underestimate the level of core damage because
the release from the core may by-pass the containment, may be retained in the primary system, may
be released over a long period of time, may not be uniformly mixed in the containment atmosphere,
or the mixture may be different than assumed in developing this procedure.' (from http://www-pub.iaea.org/MTCD/publications/PDF/te_955_prn.pdf)

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?

3. they use ONE value, that they say they have recorded 97h after SCRAM (unit 1).
this value has never been released to the public before.
if i put the earliest released readings in their diagram, i get 100% damage...
i have not checked for the other units.

4. how long was the core partially uncovered without cooling? is it reasonable, that the core damage is below 100% after this time?

i would really appreciate, if someone with a deeper knowledge than me, could comment on this.

1. agree.

2. Most sense would be to use the higher one of both readings to be on the safe side. To add them together is maybe the accumulation of the radiation on both places. Hope they asked NISA IAEA befor ;)

3. agree.

4. If you take the book word for word it could be 100 % damage in unit 1.

 

[Cainnech]

Anybody see this?

http://www.asahi.com/national/gallery_e/view_photo.html?national-pg/0426/TKY201104260415.jpg

Btw, has anyone the original map from the ministry of science? Thanks.

This one perhaps (page 2)? http://www.mext.go.jp/component/a_menu/other/detail/__icsFiles/afieldfile/2011/04/26/1305519_042618.pdf

 

[MadderDoc]

Perhaps I should ask a clearer question. From the http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110427e18.pdf", can we assume that approximately 45% of the core of Unit 1 (for example) is now in the Drywell?

I don't think the figures mean that.

If not, please could someone explain how we should interpret this data?

My understanding is that after a reactor shut down the gamma radiation dose rate in the drywell/wetwell will wane over time in a predictable fashion. If at some given point in time after the shut down, the gamma radiation is found to exceed the expected value, that can be taken as an indication of core damage. The more core damage, the more the expected values will be exceeded. One can therefore make a set of calibration curves setting out the relation between dose rate and the time since shut down, one curve for each degree of core damage.

Now, if you find that your measured combination of dose rate in the drywell and time since shut down is a point on the 10% core damage curve, then your estimate based on the drywell readings will be a core damage ratio of 10%. For the total core damage ratio, you must do the same with your wetwell readings, and add the two.

Caveat, I am not a nuclear engineer or any such thing, just a chemist with some experience in metrology.

 

[etudiant]

A nuke is also triggered by a conventional explosion. Designed very efficent but complex with only a small amount of uranium or plutonium.

No one does experiments with tons of fuel even if not highly enriched.

Some people belief that the explosion energy in Chernobyl was a result of fission.

Tests with faulty designed (bad chain reaction) nukes show that also a small explosion with only the energy of 100 tons TNT is possible.

Afaik, prompt criticalities are entirely possible when sufficient nuclear material is gathered together.
The development of that process, in an accident, would create enough heat and pressure to disassemble that material. The main difference is that a bomb is designed to confine the material much longer than it normally could be, so the nuclear reaction can proceed further.
So the idea of a nuclear event in the SFP 4 is not inherently impossible, as it was overstuffed with relatively fresh nuclear material kept moderated by boral plates. How that energetic an event could play out without blowing the bottom out of that pool is not clear.
At a minimum, the accident will make SFPs an item of intense regulatory interest. Perhaps it might even bring about a reconsideration of the Yucca Mountain repository.

 

[clancy688]

Some people belief that the explosion energy in Chernobyl was a result of fission.

I don't see any point why it shouldn't be...


The reactor was running on low power, thus being unstable. Then an power rise occurred and a SCRAM was initiated. But the graphit at the end of the control rods even increased the power and steam pipes ruptured, blocking the control rods halfway.
Then the power output increased to 30 GWt and the whole reactor went through the roof.

That's what I would call a power explosion - suddenly the reactor became overcritical, created immense amounts of thermal power in very short time and the result was a massive steam explosion which wrecked the whole building.

 

[ascot317]

Afaik, prompt criticalities are entirely possible when sufficient nuclear material is gathered together.
The development of that process, in an accident, would create enough heat and pressure to disassemble that material. The main difference is that a bomb is designed to confine the material much longer than it normally could be, so the nuclear reaction can proceed further.
So the idea of a nuclear event in the SFP 4 is not inherently impossible, as it was overstuffed with relatively fresh nuclear material kept moderated by boral plates. How that energetic an event could play out without blowing the bottom out of that pool is not clear.
At a minimum, the accident will make SFPs an item of intense regulatory interest. Perhaps it might even bring about a reconsideration of the Yucca Mountain repository.

Wouldn't we be seeing a neutron and gamma spike at the moment of the explosion then?

 

[Rive]

Some people belief that the explosion energy in Chernobyl was a result of fission.

It's a bit confusing. Please, can somebody explain it to me that what's the difference between a reactor running on several dozen times higher power than the design parameters (which , of course, will generate an explosion) and a fission generated explosion?

My usual point is if the pressure comes from steam/gas of water or from steam/gas of solid material, but it's not an 'official' difference.

 

[Samy24]

Wouldn't we be seeing a neutron and gamma spike at the moment of the explosion then?

We could only "see" this if it was massured at that time. And if it was measured it had to be published.

 

[ascot317]

We could only "see" this if it was massured at that time. And if it was measured it had to be published.

That's my point.

 

[Samy24]

That's my point.

Maybe you misunderstood me. I believe they did not measure at that time. And even if they did, i do not believe they would have published it.

 

[ascot317]

Maybe you misunderstood me. I believe they did not measure at that time. And even if they did, i do not believe they would have published it.

I'm not sure, aren't there quite a few automated counters on site? Or, aren't there any, or, since they didn't have offsite power at that time, they weren't working?

I'm not so sure, it's been a while.

 

[htf]

It's a bit confusing. Please, can somebody explain it to me that what's the difference between a reactor running on several dozen times higher power than the design parameters (which , of course, will generate an explosion) and a fission generated explosion?

Do we have a clear definition of a fission generated explosion?

The explosion of Chernobyl #4 was attributed to a hydrogen explosion. The hydrogen was generated by the overheated reactor. When they say it was "fission generated explosion" then this would mean to me that there was no hydrogen explosion. The energy came solely from an an sudden increase of the fission rate.

 

[Samy24]

I'm not sure, aren't there quite a few automated counters on site? Or, aren't there any, or, since they didn't have offsite power at that time, they weren't working?

I'm not so sure, it's been a while.

To my memory they had to check readings at the plant by "hand". Workers had to go to measuring points and look at the readings. the measurement of neutron flux ist not so easy but was indeed reported one mile away. But I do not know the point in time of that measure.

 

[default.user]

Maybe you misunderstood me. I believe they did not measure at that time. And even if they did, i do not believe they would have published it.

http://www.businessweek.com/news/2011-03-31/tepco-workers-threatened-by-heat-bursts-sea-radiation-rises.html

 

[Samy24]

http://www.businessweek.com/news/2011-03-31/tepco-workers-threatened-by-heat-bursts-sea-radiation-rises.html

What should this "light" proof? The explosion was at daylight.

 

[clancy688]

It's a bit confusing. Please, can somebody explain it to me that what's the difference between a reactor running on several dozen times higher power than the design parameters (which , of course, will generate an explosion) and a fission generated explosion?

I'd say there is no difference. Except for the generated power. A nuclear reactor uses fission to generate heat which's used to power a turbine.
A nuclear weapon uses fission to generate massive amounts of heat to forge a devastating shock wave.
It's the same reaction. It's the same output. Only the nuclear weapon uses the reaction on a far bigger scale... more fission, more neutrons, more heat, more energy. A lot more energy.

The explosion of Chernobyl #4 was attributed to a hydrogen explosion. The hydrogen was generated by the overheated reactor. When they say it was "fission generated explosion" then this would mean to me that there was no hydrogen explosion. The energy came solely from an an sudden increase of the fission rate.

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 - because that's how long it took Chernobyl to change from a perfect healthy reactor into a pile of rubble.
And I don't think that such a fast reaction would be possible.Edit:
@Samy24 - Cherenkov radiation, water glows blue when radiation passes through it. But I don't think it proves anything. First, the images were enhanced to show the spot. I couldn't detect anything. And I don't think that enhancing a crappy webcam pic will show us anything. Second, it seems to be normal for SFPs, even without criticality.

 

[default.user]

What should this "light" proof? The explosion was at daylight.

It should be a proof for neutron radiation.

Accordingly, there had been partial criticality.

The image was sharpened and subsequently processed..

http://www.sueddeutsche.de/wissen/japan-nachbeben-der-staerke--1.1075927

A german newspaper. A good one. I translate with the google translator:

The operating company Tepco said on Wednesday that it had in 1.5 kilometers away from the reactor neutron beams measured a total of 13 times on the site, indicating a withdrawal of the radioactive material

http://en.wikipedia.org/wiki/Neutron_radiation#Sources

Neutrons may be emitted from nuclear fusion or nuclear fission, or from any number of different nuclear reactions such as from radioactive decay or reactions from particle interactions (such as from cosmic rays or particle accelerators). Large neutron sources are rare, and are usually limited to large-sized devices like nuclear reactors or particle accelerators (such as the Spallation Neutron Source).

So we still have high temperatures in the reactors.
The neutron beams were visible until Tuesday of this week.

i wrote it with the google translator.

Sorry

 

[TCups]

Question for Astronuc et al:

As I think about this, if the shape and depth of the SFP could focus the blast into a vertical mushroom, then the shape and depth of the SFP, particularly if there were water covering all or part of the spent fuel would also tend to focus the force of an explosion toward the bottom of the SFP. Might it be that either a blast from the primary containment or a blast from hydrogen + air in the service floor, "amplified" by the geometry of the SFP and efficiently transmitted by water in the SFP did indeed exert a hydrostatic, crushing force on the spent fuel assemblies?

This wouldn't be a shaped HE charge crushing two subcritical hemispheres of plutonium, but on a much larger scale, a large explosion crushing several tons of spent fuel racks -- at least in theory, the hypothesis of a sudden criticality in the SFP doesn't seem too far fetched to a lay person.

 

[Samy24]

Edit:
@Samy24 - Cherenkov radiation, water glows blue when radiation passes through it. But I don't think it proves anything. First, the images were enhanced to show the spot. I couldn't detect anything. And I don't think that enhancing a crappy webcam pic will show us anything. Second, it seems to be normal for SFPs, even without criticality.

I was responding because we talked about the posibility that the explosion on unit 3 was driven also by fission. The explosion was at daylight so the Cherenkov light (if it is) has nothing to do with it. Someone asked why they did not detect gamma and neutron bursts at the time of the explosion and so default.user kicked in.

 

[PietKuip]

I'd say there is no difference. Except for the generated power. A nuclear reactor uses fission to generate heat which's used to power a turbine.
A nuclear weapon uses fission to generate massive amounts of heat to forge a devastating shock wave.
It's the same reaction. It's the same output. Only the nuclear weapon uses the reaction on a far bigger scale... more fission, more neutrons, more heat, more energy. A lot more energy.

In a real nuclear bomb, the chain reaction occurs by fast neutrons. One needs highly enriched uranium for that, or plutonium.

In an ordinary nuclear reactor, the chain reaction proceeds because of fission induced by thermal ("slow") neutrons. One wants to keep the criticality factor below 1.006. This ensures that "delayed" neutrons are necessarry to keep the chain reaction going, so that it can be controlled by manipulating control rods.

But when k > 1.006, one has prompt criticality, and rapid exponential growth of power, too fast for control rods to limit. It is only limited by the moderator dissappearing and/or the critical mass being dispersed by the heat generated. A nuclear "fizzle" by slow neutrons, but much more violent than an Oklo-type of criticality.

 

[Samy24]

Question for Astronuc et al:

As I think about this, if the shape and depth of the SFP could focus the blast into a vertical mushroom, then the shape and depth of the SFP, particularly if there were water covering all or part of the spent fuel would also tend to focus the force of an explosion toward the bottom of the SFP. Might it be that either a blast from the primary containment or a blast from hydrogen + air in the service floor, "amplified" by the geometry of the SFP and efficiently transmitted by water in the SFP did indeed exert a hydrostatic, crushing force on the spent fuel assemblies?

This wouldn't be a shaped HE charge crushing two subcritical hemispheres of plutonium, but on a much larger scale, a large explosion crushing several tons of spent fuel racks -- at least in theory, the hypothesis of a sudden criticality in the SFP doesn't seem too far fetched to a lay person.

So I see that too. Maybe it's not very likely. But to simply say it is impossible is also not correct. No one has tried this with more the 100 tons of fuel before. (This test would be to expensive ;)

 

[default.user]

My idea is:

The corium is much larger than we think. This means that the meltdown is far greater, indicating a TEPCO.

The corium has enough mass to trigger a partial criticality. So that the temperature in the reactor increases. The benefit of a further meltdown. This means that more fuel enters the reactor bottom. This leads to continuous partial criticality.
For this I need not have studied physics. The moderator boron is not in the core of the Corium 50 tons.

http://en.wikipedia.org/wiki/Corium_(nuclear_reactor)

 

[Jorge Stolfi]

I admit, this video stutters distractingly. However, the keyframes are actually pretty good, and they depicture objects we have not had a good view of before, from a so far unseen angle, and with a resolution down to a few centimeters at its best.

I do not understand the point of making videos of what is basically a static target. I would much prefer a few high-resolution photos, from well-planned vantage points (like those invaluable pics taken by the Air Photo Service drone last month) than thousands of low-resolution frames with lots of distracting MPEG artifacts.

 

[biffvernon]

Wouldn't we be seeing a neutron and gamma spike at the moment of the explosion then?

Maybe there was a spike:

On two occasions radiation levels at Dai-Ichi reached 1 sievert an hour. Thirty minutes of exposure to that dose would trigger nausea. Contamination for four hours might lead to death within four months, according to the U.S. Environmental Protection Agency.

Five kilometers away at the nuclear safety agency’s offsite center, Yokota said radiation levels set off a constant warning ping at detectors in the office, so he put on his DuPont Co. Tyvek protective suit and a face mask.

From http://www.bloomberg.com/news/2011-04-25/japan-s-terrifying-day-saw-unprecedented-exposed-fuel-rods.html

 

[elektrownik]

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...

 

[ascot317]

[...]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...

Yeah, although they apparently haven't done a complete search of the area yet (otherwise they wouldn't accidently find debris more than a month later).

What puzzles me about a "fuel-fizzle" is, the SFP is in one of the least damaged corner of the building.

Maybe there was a spike:


From http://www.bloomberg.com/news/2011-04-25/japan-s-terrifying-day-saw-unprecedented-exposed-fuel-rods.html

He shuttled between the offsite and the Dai-Ichi bunker. When the No. 3 reactor housing exploded on the morning of March 14, levels inside the bunker jumped as much as 12-fold, he said, checking dates and times in a pocket diary.

"Inside the bunker", yeah, gamma spike.

 

[Rive]

Thanks for the ideas about fission/not fission difference.

About explosion/recriticality: IMHO every explosion were hydrogen explosion and maybe containment damage, but none of them were originated directly from any SFP. It would scatter at least some fuel, and scattered/damaged fuel rods would cause much more serious contamination nearby than the actually observed. It would end in Chernobyl-style radiation zones around the affected unit (with much stronger Uranium and Plutonium presence).

However low scale pulsing recriticality by Tokaimura-style cannot be excluded. But: it cannot be proved too. IMHO.

About the picture of blue flash: fresh spent fuel is glowing even without recriticality, so without further observations it proves nothing. Is the glowing still visible? Has it happened any more times? Any similar observations from satellites, maybe?

 

[elektrownik]

The idea of "nuclear explosion" or I should say massive recricitality is interesting, also in case of Chernobyl and Fukushima. For example we have research reactor in Poland, science many years it was runing on 80% enriched uranium, from the last refuling they change it to 36%, I think that 80% wouldn't be safe in case of accident... 80% is enought for nuclear bomb

 

[Samy24]

The idea of "nuclear explosion" or I should say massive recricitality is interesting, also in case of Chernobyl and Fukushima. For example we have research reactor in Poland, science many years it was runing on 80% enriched uranium, from the last refuling they change it to 20%, I think that 80% wouldn't be safe in case of accident... 80% is enought for nuclear bomb

It is terrible to hear what experiments are done in europe. Who will take the responsibility if something happens? Is this military or private stuff?