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.