Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[Quim]

Nope. There is simply too much heat produced (and will be produced). What is there is still able to get through many meters of whatever you want to put under. Note, that the fuel has very high density, so whenever it will melt substances surrounding it it will sink deeper, replacing them. Contrary to what you think it will be not contained, sooner or later it will end in the groundwater.

That's not what happened in the only other comparable circumstance.
Why would it happen here?

These core loads have had three months to bleed off nuclides.
At that other place the dried out material started out in life as a core developing full power.


Let's see some math, or are the formulas yet to be developed? (as a result of the Fukushima incident)

 

[Astronuc]

Arm chair, I understand what you say and I don't argue with it, but what happens with Unit 3 Corium? That has MOX in it, do we know what percentage of MOX they used? And what type of Plutonium they used? 90% weapons grade? if so, what was the composition of the MOX. I am extremely concerned about the high experimental nature of the MOX as a fuel, due to the higher cross sectional area of Pu-239 for neutron absorption, and the zero data that we have on accidents of this nature involving MOX... Also, the short lived use of the reactor since it was restarted in Setember 2010 up to March's accident means that most Pu was still there...
I'd love to hear other experts comments on this topic...

There has been considerable use of MOX fuel in light water reactors (LWRs).

It was reported that there were 32 MOX fuel assemblies in Unit 3, or about 6% of the core of 548 assemblies. They were operating in their first cycle, so they didn't have much operation/exposure. Ostensibly, the MOX fuel was derived from spent fuel from the Fukushima reactors, thus it was reactor grade, and the Pu isotopics would have reflected that legacy. The MOX fuel would be designed to match the enrichment of the U-235 assemblies, which is about 4% U-235. So likely the MOX would be about 6% Pu, with a mix of Pu239, 240, 241 and 242.

Spent fuel contains Pu isotopes. The use of MOX is rather insubstantial to the event and the current state of Unit 3.

 

[tsutsuji]

A new theory for unit 1 explosion :

TEPCO officials believe hydrogen gas that should have been released from the vent pipe flowed back into the reactor building through the open SGTS valve after reaching the point where the two exhaust systems converge.
http://www.asahi.com/english/TKY201106040165.html

 

[etudiant]

You raise a valid concern.
Yet, these "puddles" are already three months old and they will decline in heat generation from here on out (sans criticalities.)

But you are absolutely correct that somebody needs to attempt the actual math behind the premise I am proposing.

A problem could be expected to develop if the corium is still contained in the RPVs and all the water goes away - the corium would then only have air as a heat sink. That wouldn't be acceptable for the reason you raise.

But I bet there are ways of dealing with that circumstance cheaply and without endangering anyone's health. Be it lead or sand or something else, the RPVs will need something in them other than corium and air.

I believe that can be done.

My $0.02 is that someone did do the math and concluded that your belief is mistaken.
We are looking at 4 to 6 megawatts per core of residual heat per core, more than enough to boil that core if the heat is not removed continuously. Adding lead is useless, it may be a great shield but it melts at low temperature and emits toxic fumes. Ditto sand, no toxic fumes but no cooling either. Because it is decay heat, no outside material such as boron will help. We are lucky that water is cheap, non toxic and has a high heat capacity.. It is cooling this mess reasonably well and our only problem is that we are running out of places to store the used water. That is a high class problem relative to the question of how do you control boiling radio nucleotide vapors.

 

[rmattila]

In an BWR, I believe, the feedwater line also enters above the top of the fuel.

Above the top of the core, but outside the shroud (=in the downcomer region) where the cooler feedwater mixes with the recirculation flow to provide some suction head for the recirculation pumps. At least this is the case with reactors with internal recirculation pumps, which I am familiar with.

The core spray system, which I believe the fire extinguisher system at Fukushima is lined up to, ends up inside the shroud and actually sprays the water on top of the fuel, not into the downcomer (from where it may flow out of the reactor through leaking main circulation pump seals and never reach the actual core region).

 

[Quim]

My $0.02 is that someone did do the math and concluded that your belief is mistaken.

"Your assumption is that someone did the math....."I assume otherwise.Or to take the advice of Bill Gates: "assume nothing"**This is a assembly directive in the MS assembly language which exists in the form of "assume nothing."

To make a long story short, it accomplishes nothing, it would have only been included as an assembly directive because Mr. Bill was trying to tell us something.

 

[Luca Bevil]

Quick question:

Fission yield from U 235 are quite similar for Cs 134 (6,78%) and CS 137 (6,08%) according to wikipedia.

Given the shorter half life of CS134, though, activity of CS134 is much higher: 47.864 Tbq/g (CS 134) vs 3.214 Tbq/g (Cs 137).

Even after taking into account the faster decay, during the average time likely spent since fission, I would have expected CS134 contribution to water radioactivity being quite higher than CS137 contribution.

However data TEPCO released a few days ago about basement 1 contamination had estimates for CS137 bq/cc and CS 134 Bq/cc very close to each other.

How would that be explained ?

 

[rmattila]

Quick question:

Fission yield from U 235 are quite similar for Cs 134 (6,78%) and CS 137 (6,08%) according to wikipedia.

Very little Cs-134 is produced directly in fission, and most of it is produced by neutron capture of the more common (stable) fission product Cs-133. The value 6,78 % is the combined yield of Cs-133 and Cs-134. How much of Cs-133 is converted to Cs-134 depends on the burnup of the fuel.

 

[Astronuc]

Quick question:

Fission yield from U 235 are quite similar for Cs 134 (6,78%) and CS 137 (6,08%) according to wikipedia.

Those should be the cumulative yield based on the decay chains (and transmutations) leading to the respective isotopes.

Given the shorter half life of CS134, though, activity of CS134 is much higher: 47.864 Tbq/g (CS 134) vs 3.214 Tbq/g (Cs 137).

Even after taking into account the faster decay, during the average time likely spent since fission, I would have expected CS134 contribution to water radioactivity being quite higher than CS137 contribution.

However data TEPCO released a few days ago about basement 1 contamination had estimates for CS137 bq/cc and CS 134 Bq/cc very close to each other.

How would that be explained ?

The Cs-134/Cs-137 ratio depends upon burnup. In the Fukushima cores, there are perhaps four batches of fuel representing four populations of burnup, and each will have a different accumulation of the Cs-134 and Cs-137. The actual ratio of Cs in the coolant will be a weighted sum of the source terms of those assemblies that failed.

 

[etudiant]

"Your assumption is that someone did the math....."


I assume otherwise.


Or to take the advice of Bill Gates: "assume nothing"*


*This is a assembly directive in the MS assembly language which exists in the form of "assume nothing."

To make a long story short, it accomplishes nothing, it would have only been included as an assembly directive because Mr. Bill was trying to tell us something.

Excellent approach. Mr Gates is a good guide.
So we have 3 reactor cores, each dissipating about 6 megawatts of residual decay heat (4 in the case of unit 1, which is much smaller). That will continue for the next few years largely unchanged, albeit with a modest downward trend. Assume the cores are hot, but not yet melted, at around 1000 degrees Kelvin.
A reactor core is about 100 tons of uranium oxide, plus additives. Uranium oxide has a specific heat of 240 joules/kg per degree K. So we have 100,000 kg of fuel producing 6 megawatts of heat, or 6 million joules/second. Heating the fuel 1 degree will take 240 * 100,000 joules, or 24 million joules, about 4 seconds worth of heat output. So to heat the fuel to the boiling point, somewhere around 4000 degrees Kelvin, will take 3000 times that long, about 12,000 seconds, less than 4 hours.
I'd recommend sticking with the water option.

 

[MiceAndMen]

The spent fuel must be removed from the SFPs of Units 1-4 in and placed in casks. That can only happen after the debris is removed, and most likely will have to be done remotely, and possibly robotically.

That is going to be a challenging task, to say the least. At some point the bundles are going to have to be lifted out of the SFP water completely and moved through the open air, at least for a short period of time. Assuming they are not dropped while in transit, what are the consequences of a spent fuel bundle being transported through the air for a short time without any water shielding it?

 

[jim hardy]

""I'd recommend sticking with the water option.""

Thank you Etudiant. That is the kind of step-by-step thinking and explanation that made Isaac Asimov so popular. Nice post.

old jim

 

[Astronuc]

That is going to be a challenging task, to say the least. At some point the bundles are going to have to be lifted out of the SFP water completely and moved through the open air, at least for a short period of time. Assuming they are not dropped while in transit, what are the consequences of a spent fuel bundle being transported through the air for a short time without any water shielding it?

Not necessarily. If there is water in the SFP and the cask pit, the assemblies can be transferred underwater. However, if the SFP water is contaminated, i.e., if it has dissolved fission products and some fuel in it, then decontamination of the case becomes an issue. However, there is no fuel handling machine in place with which to do this work, so it would have to be done with some kind of crane based on the grounds outside of the reactor building, unless TEPCO somehow removes the debris from the reactor service floor and basically builds a new transfer system.

We still don't know the state of the fuel in the SFPs of units 1, 2 and 3. The images of SFP #3 show a lot of debris in the pool. I have not seen images from SFP of Units 1 or 2.

 

[Atomfritz]

Why?
Why not let it reach its own equilibrium?
Hot sand, gravel, concrete or dirt is no threat to anything or anyone.

This also has been done in Chernobyl.

As the molten mass gets in touch with other stuff, it appears very probable that it sucks up impurities, reducing heat density until the point where it gets so cold that no more melting does happen.

Everybody knows the infamous "Elephant Foot".
Two lesser known images of molten mass from the (in)famous Ukrainian accident:

Isn't it amazing that the tubes where this hot (2300 C) mass flowed out didn't break?
( Pictures taken from page 28 of this http://tec-sim.de/images/stories/severe-accident-phenomenology.pdf" )


I start asking myself how much a part of the short-lived fission products already has been washed out from the core, and now flooding the basement etc.
Maybe the "corium" possibly already is way less "hot" than "freshly molten core"?

If, say, 5 MW of total 6 MW of decay heat has been dispersed in 10,000 cubic meters of water this would equal 500W per cubic meter. Probably not a big problem, probably the heat is easily dissipated by big surface, convection and (slow) vaporization, and so practically gets unnoticed.

So, if the residual heat of a hypothetical complete core is about 6MW now (taking into consideration the fission product decay heat) then the actual heat being developed where the (remaining) core is, could be substantially less, maybe 1 MW?

If the molten mass gets sufficiently dispersed with other stuff it will eventually get below the melting point.
Even if the mass tends to keep a inner liquid hot core, it eventually will lose mass due to parts it loses on its way. "China Syndrome" is just panic-mongering imo.

They are just caught in the problem that they do not know in what shape the core remains are.
It just depends on the geometry.
If there is a very big very flat splash of metal on the floor, then the situation is way different if it's concentrated in a near-round drop-like form.
Probably very good also could be if the floor is covered with lots of small blobs with large crusty surface, dispersed regularly on the floor, as was observed when TMI cleanup people finally got to the RPV floor.

I guess they just cannot stop watering the cores until they can be sure that there is no longer a risk of more melting stuff dropping into water, causing a steam explosion?

Too bad there are no optical means of remote-inspecting the containment without opening/entering it.

Maybe the Tepco strategy is
-to just wash out the cores from the short-lived fission products to...
-then to be able to let the core remains dry out soon
-finally to leave them alone, to be entombed asap?

 

[Bioengineer01]

There has been considerable use of MOX fuel in light water reactors (LWRs).

It was reported that there were 32 MOX fuel assemblies in Unit 3, or about 6% of the core of 548 assemblies. They were operating in their first cycle, so they didn't have much operation/exposure. Ostensibly, the MOX fuel was derived from spent fuel from the Fukushima reactors, thus it was reactor grade, and the Pu isotopics would have reflected that legacy. The MOX fuel would be designed to match the enrichment of the U-235 assemblies, which is about 4% U-235. So likely the MOX would be about 6% Pu, with a mix of Pu239, 240, 241 and 242.

Spent fuel contains Pu isotopes. The use of MOX is rather insubstantial to the event and the current state of Unit 3.

Do you have any links to this data? Early on in the accident I saw some export permits issued to AREVA from the USA to export MOX to Fukushima Daiichi, Japan that don't fit into your description, but eventhough, the timing was correct, I have no way of knowing whether they ended up in Unit 3 or not. That was NOT fuel derived from spent fuel...

 

[Quim]

This also has been done in Chernobyl......

I guess they just cannot stop watering the cores until they can be sure that there is no longer a risk of more melting stuff dropping into water, causing a steam explosion?

Too bad there are no optical means of remote-inspecting the containment without opening/entering it.

Maybe the Tepco strategy is
-to just wash out the cores from the short-lived fission products to...
-then to be able to let the core remains dry out soon
-finally to leave them alone, to be entombed asap?

Thank you for putting that in writing.
I am in agreement with your assessment.
I bet everyone else agrees too.

I suspect that the "plant guys" (there and here) are somewhat stuck in a vision of units 1, 2 and 3 which no longer exists. The "plant guys" want to put three nuclear reactors into cold shutdown.

But there are no longer any reactors in buildings 1,2 and 3 and there never will be any reactors in those buildings ever again. The paradigm has shifted, and to some extent we are all on equal footing here, plant guys and non-plant guys.

This is a corium isolation problem, not a NPP problem anymore.
Plant guys are very procedure oriented, they have to be in order to be plant guys.
But this situation has no procedures to follow.
It requires a different kind of analysis.
IMO.

 

[Astronuc]

Do you have any links to this data? Early on in the accident I saw some export permits issued to AREVA from the USA to export MOX to Fukushima Daiichi, Japan that don't fit into your description, but eventhough, the timing was correct, I have no way of knowing whether they ended up in Unit 3 or not. That was NOT fuel derived from spent fuel...

AREVA does not fabricate MOX fuel in the US.

Please post the export permits that one 'saw'.

TEPCO has reprocessing contracts with AREVA. There is strict control of spent fuel and MOX fuel. TEPCO indicates that MOX is derived from spent fuel.
http://www.tepco.co.jp/en/challenge/csr/nuclear/cycle-e.html

The status of MOX fuel is posted earlier in this thread.

 

[SteveElbows]

I suspect that the "plant guys" (there and here) are somewhat stuck in a vision of units 1, 2 and 3 which no longer exists. The "plant guys" want to put three nuclear reactors into cold shutdown.

I for one am neither a 'plant guy' nor am I stuck with some false and outdated vision of the reactors in my mind.

I believe the cores require cooling. You have not demonstrated otherwise, and attempts to dismiss this issue by using some dismissive 'plant guys' label do not help your case any.

Only as the story unfolds will we truly be able to judge whether a terrible mistake has been made with balancing the issues of cooling and containment. Given that it does not appear that large quantities of radioactive horror are escaping the plant daily by air, how the ever-growing quantities of water are managed will likely be a key factor in determining whether the approach taken has been a mistake or not.

 

[jim hardy]

it's a problem of moving 6 megawatts of heat while minimizing water.

to that end letting it make steam is best solution.

A kilogram of 100C steam carries away 2676 Kilojoules, but the same weight of 100C water only 419. Less if you started with already warm water.

So by steaming they reduce the amount of water to be handled probably tenfold.
and they get benefit of distillation, to help contain the contamination.

give them some credit for knowing what they are doing. they weren't born yesterday.

i learn a lot by watching intelligent people work and figuring out why they do what they do..
Mother Nature is a tough schoolmistress - she makes one work for her lessons.

 

[Atomfritz]

I suspect that the "plant guys" (there and here) are somewhat stuck in a vision of units 1, 2 and 3 which no longer exists. The "plant guys" want to put three nuclear reactors into cold shutdown.

But there are no longer any reactors in buildings 1,2 and 3 and there never will be any reactors in those buildings ever again.

Really good observation.
You remind me what happened in russia then...
Mr. Dyatlov, manager of the blown-up block in Chernobyl insisted that the reactor was still there, intact, being cooled.
He was unable to be convinced that the reactor was damaged until helicopters filmed the situation from above next noon.
This delayed many emergency measures.

The paradigm has shifted, and to some extent we are all on equal footing here, plant guys and non-plant guys.
...
But this situation has no procedures to follow.
It requires a different kind of analysis.

In Russia military quickly took over to remedy the situation.
In Fukushima also constantly new procedures are being developed.

First step should always be a thorough assessment of the situation.
Then the necessary measures must be developed or improvised.
Layman input at least is not restricted by procedure thinking obsoleted by new situations.

So to get back to the reactor problem:
There are questions not asked before even in this thread.

What fraction of the short-lived fission products can be expected to already have left the reactors and taken away by the cooling water?

If, for example, as some sources say, almost all iodide and cesium has been dissolved into the tens of thousands cubic meters of water, then a big part of the residual heat could now have left the reactor remains.

So my second and third question:
Does this bleed-out of FPs reduce residual heat substantially?
If so, what magnitude could be the probable reduction of core remains' residual heat?

Why I ask this:
There will eventually be a point of equilibrium when the heat can sufficiently passively dissipate through floors, walls etc slowly without melting anything more.
From this point on, the way most economical solution would be entombing.I'd be happy if some nuclear professional could comment on how much of the FP inventory is still in the reactors.
Thank you!

 

[MiceAndMen]

AREVA does not fabricate MOX fuel in the US.

Please post the export permits that one 'saw'.

TEPCO has reprocessing contracts with AREVA. There is strict control of spent fuel and MOX fuel. TEPCO indicates that MOX is derived from spent fuel.
http://www.tepco.co.jp/en/challenge/csr/nuclear/cycle-e.html

The status of MOX fuel is posted earlier in this thread.

I think TEPCO has plans to formulate their own MOX fuel in the future, but I was also under the impression that the MOX fuel in use there currently came from AREVA and shipped from France.

http://www.world-nuclear-news.org/ENF-Japan_starts_using_MOX_fuel-0511094.html

So up until now, it was devrived from Japanese spent fuel and it did come from France. Both statements are true.

 

[SteveElbows]

Yeah, there are not too many places that make MOX fuel. This article is about a year old and says:

Sellafield MOX Plant is one of only two commercial MOX fuel manufacturing plants in the world, the other being Melox at La Hague in France. One called J-MOX is approved for build in Japan, and construction is underway on another at Savannah River in the USA but this is for the destruction of plutonium from former weapons stocks. Small facilities operate at Tokai in Japan and Marak in Russia.

Taken from http://www.world-nuclear-news.org/WR_Japanese_firms_stick_with_Sellafield_MOX_Plant_1305101.html

Also we can see how the MOX stuff has been a very slow process with many delays along the way, with this article which seems to be over a decade old:

http://www.atimes.com/japan-econ/AI18Dh01.html

The ships are expected to be make their first stop at the pier of the No 1 Fukushima nuclear power plant of Tokyo Electric Power Co in Fukushima. The vessels will then be at Takahama nuclear power plant of Kansai Electric Power Co by the Sea of Japan on September 27. The ships are carrying armed British soldiers, who will have to be disarmed before entering Japanese waters, after which the vessels will be accompanied by Japan's Self Defense Forces.

 

[Atomfritz]

AREVA does not fabricate MOX fuel in the US.

Please post the export permits that one 'saw'.

TEPCO has reprocessing contracts with AREVA. There is strict control of spent fuel and MOX fuel. TEPCO indicates that MOX is derived from spent fuel.
http://www.tepco.co.jp/en/challenge/csr/nuclear/cycle-e.html

The status of MOX fuel is posted earlier in this thread.

I think the background is that the original fuel was delivered by the USA, and the contracts forbiding japan to export it without US license/permit (NPT stuff etc).
So japan had to obtain export licenses/permits from the USA to have reprocess it by Cogema in La Hague and to get it packaged by Melox in Marcoule.
Afaik this is common with all countries the USA sell nuclear fuel to.
Nothing abnormal.
They stopped sending fuel to reprocess to Europe in 1999 in anticipation of their own reprocessing plant in Rokkasho.
Maybe these details are lesser-known to Americans, as they don't have these import/export problems.

Btw, I really doubt that the 210kg reactor grade plutonium in reactor 3 (extracted from fuel with burnup of about 3x MWd, comparatively low burnup) make the situation much worse.
Considering the lots of dirty high-burnup fuel looming under the sky, possibly containing even more plutonium to worry about than that contained in the RBs...

 

[MiceAndMen]

That's not what happened in the only other comparable circumstance.
Why would it happen here?

These core loads have had three months to bleed off nuclides.
At that other place the dried out material started out in life as a core developing full power.

Let's see some math, or are the formulas yet to be developed? (as a result of the Fukushima incident)

There has been considerable math and forumlas developed, but there are still a lot of unknowns. Kids not even born yet will be writing their PhD theses about Fukushima a few decades from now.

Anyone interested in the corium aspects of this situation should have a look at the following pdf reports:

http://www.tec-sim.de/images/stories/lecturenotes-late-in-vessel-phenomena.pdf
http://www.tec-sim.de/images/stories/severe-accident-phenomenology.pdf

They are fairly recent and summarize the current state of knowledge regarding "corium". The most interesting thing I found out, is that 25 years after TMI2 there is still no explanation for why the molten corium did not melt through the reactor vessel. All simulations indicate that it should have happened, but it didn't. To this day nobody can explain it. There is a lot we don't know.

 

[Astronuc]

I think the background is that the original fuel was delivered by the USA, and the contracts forbiding japan to export it without US license/permit (NPT stuff etc).
So japan had to obtain export licenses/permits from the USA to have reprocess it by Cogema in La Hague and to get it packaged by Melox in Marcoule.
Afaik this is common with all countries the USA sell nuclear fuel to.
Nothing abnormal.
They stopped sending fuel to reprocess to Europe in 1999 in anticipation of their own reprocessing plant in Rokkasho.
Maybe these details are lesser-known to Americans, as they don't have these import/export problems.

Btw, I really doubt that the 210kg reactor grade plutonium in reactor 3 (extracted from fuel with burnup of about 3x MWd, comparatively low burnup) make the situation much worse.
Considering the lots of dirty high-burnup fuel looming under the sky, possibly containing even more plutonium to worry about than that contained in the RBs...

I'm not sure if the MOX fuel came from AREVa supplied spent fuel. However, it's possible that the spent fuel from which the MOX was derived came from uranium enriched in the US. In that case, the DOE has some restrictions on that fuel.

The Japanese have had reprocessing contracts with BNFL and AREVA/Cogema, but basically AREVA fabricates BWR fuel. AREVA-US did supply some fuel to TEPCO, as far as I know, but I'm not sure which unit.

 

[jim hardy]

i think it was made by Belgonucleaire in Belgium.
http://www.belgonucleaire.be/uk/mox.htm
http://www.belgonucleaire.be/files/PR-310101.doc

and it's my opinion that the hype about MOX is just that, scaremongering hype..

 

[MiceAndMen]

TEPCO revises theory about hydrogen explosion at Unit 1

http://www.asahi.com/english/TKY201106040165.html

In short, they think that when the primary containment was vented, the hydrogen looped back around at some point before reaching the stack, and flowed back into the building through the Standby Gas Treatment System (SGTS) ducts because of a stuck valve.

They cite this as a possible design deficiency, but if the total loss of power (station blackout) was a beyond-design-bases event then it's not something they would have designed for in the first place. I don't see how that amounts to a design defect (that's not to say the design bases were sufficiently robust).

It's remarkable how every single news report coming out of Japan seems to suffer from either mixed-up terminology, ambiguity, or in this case, outright non sequiters.

When the No. 1 reactor began operations in 1971, it had an exhaust system to release gas from the reactor building. After the 1986 nuclear accident at Chernobyl, the exhaust system for the containment vessel was installed in 1999 as a measure to prevent a severe accident.

The upgraded hardened vent systems had everything to do with revised BWR containment safety concerns and absolutely nothing to do with Chernobyl. Who comes up with this stuff?

Isaac Asimov was the master at explaining things, and i always try to imitate the 'one step at a time' thinking i learned from his writings. One comes to appreciate just how imprecise and inconsistent English language can be at painting accurate pictures in our mind.

I wonder if the Japanese language might even be worse in that regard. Even some of the so-called "perfect" translations we've seen of some reports seem to suffer from the same imprecision and lack of consistency. But I'm not a linguist, so who knows.

(OT: I cherish the memory of the time I met Asimov in NYC many moons ago.)

 

[Jorge Stolfi]

These core loads have had three months to bleed off nuclides.

Only a small portion of the radioactive, heat-producing nuclides should have left the fuel mass since the acident began.

Surely this variable has been studied by experts; although it must be hard to get a good estimate starting with so many unknown parameters.

My ignorant guess is that at most 10% of the radioactiv load has left the fuel mass so far; and that only if the uranium oxide melted so that the volatile elements (such as Cs and I) trapped in its atomic lattice were able to escape.

As etudiant's simple math showed, the core loads are still sitting there only because their heat output has been diverted into boiling off several tons of water per hour.

 

[Jim Lagerfeld]

New analysis introduced on the front page of today's Tokyo Shimbun puts the disparity between explosions in reactor buildings one and three down to the concentration and of hydrogen - 15% in building 1 one vs 30% in building 3:

http://tinyimage.net/images/54067954849412280308_thumb.jpg

Sorry I don't have a scanner available today.

The headline reads: 「Reactor number 3's explosion was a "detonation"」

The graphic shows hydrogen @ 15% in building one combusting over 'several seconds' vs hydrogen @ 30% detonating in '0.02 seconds' in building 3.

 

[Jorge Stolfi]

Anyone interested in the corium aspects of this situation should have a look at the following pdf reports:

http://www.tec-sim.de/images/stories/lecturenotes-late-in-vessel-phenomena.pdf
http://www.tec-sim.de/images/stories/severe-accident-phenomenology.pdf

Fascinating info and pictures. Many thanks!

 

[Quim]

Only a small portion of the radioactive, heat-producing nuclides should have left the fuel mass since the acident began.

The heat decays at an exponential rate.

http://en.wikipedia.org/wiki/Decay_heat#Power_reactors_in_shutdown

(t)

 

[MiceAndMen]

Fascinating info and pictures. Many thanks!

This is probably a good time for me to add my thanks for keeping those data plots for all those weeks. Don't feel too bad about whether or not the source data was accurate; your efforts were not wasted IMO.

 

[dh87]

Only a small portion of the radioactive, heat-producing nuclides should have left the fuel mass since the acident began.

Surely this variable has been studied by experts; although it must be hard to get a good estimate starting with so many unknown parameters.

My ignorant guess is that at most 10% of the radioactiv load has left the fuel mass so far; and that only if the uranium oxide melted so that the volatile elements (such as Cs and I) trapped in its atomic lattice were able to escape.

As etudiant's simple math showed, the core loads are still sitting there only because their heat output has been diverted into boiling off several tons of water per hour.

I am not sure that your statement that the volatile elements would be trapped if the uranium oxide remained solid is correct. Wikipedia says, "In the oxide fuel, intense temperature gradients exist which cause fission products to migrate. The zirconium tends to move to the centre of the fuel pellet where the temperature is highest, while the lower-boiling fission products move to the edge of the pellet. The pellet is likely to contain lots of small bubble-like pores which form during use; the fission xenon migrates to these voids. Some of this xenon will then decay to form caesium, hence many of these bubbles contain a large concentration of 137Cs." (http://en.wikipedia.org/wiki/Spent_nuclear_fuel) If Wiki is right, then the used fuel will contain "bubbles" with high concentrations of Cs. These would be under high pressure if the temperature rises to 1500 °C, which is above the boiling point for most likely Cs compounds. Also, a three-month immersion in boiling water (sometimes in boiling salt water) is a really good way to do extractions.

My argument doesn't invalidate your guesstimate of 10%, but my guesstimate would be higher.

 

[rowmag]

TEPCO revises theory about hydrogen explosion at Unit 1

http://www.asahi.com/english/TKY201106040165.html

In short, they think that when the primary containment was vented, the hydrogen looped back around at some point before reaching the stack, and flowed back into the building through the Standby Gas Treatment System (SGTS) ducts because of a stuck valve.

They have already backed off from this theory:

http://www.asahi.com/special/10005/TKY201106040552.html

They realized there is another valve in the system which should have closed automatically when power was lost.

It's remarkable how every single news report coming out of Japan seems to suffer from either mixed-up terminology, ambiguity, or in this case, outright non sequiters.
The upgraded hardened vent systems had everything to do with revised BWR containment safety concerns and absolutely nothing to do with Chernobyl. Who comes up with this stuff?

The original Japanese suggests (to me) that the lesson learned from Chernobyl was a general one about putting more thought into preparing for severe accident scenarios, not necessarily the specific one about hydrogen vents:

http://www.asahi.com/special/10005/TKY201106030574.html

I wonder if the Japanese language might even be worse in that regard. Even some of the so-called "perfect" translations we've seen of some reports seem to suffer from the same imprecision and lack of consistency. But I'm not a linguist, so who knows.

I'm not a linguist either, but: English and Japanese both have areas which are naturally ambiguous (as, presumably, do all languages), and these areas don't necessarily match up between the two languages, so translations in either direction tend to end up making those ambiguities stand out. For example, if an English speaker refers to "my brother," the translator into Japanese will be stuck as to whether to translate this as "older brother" or "younger brother," since there is no word that just means "brother." (Maybe they would just give up and go with the word for sibling, which makes even the gender ambiguous.) In the reverse direction, the Japanese word "ao" means both blue and green, which can present a problem for a translator into English. (Sometimes context can help: is it a green light (ao shingou) or a blue sky (ao zora)?)

A very precise translation in either direction is apt to end up sounding a bit stilted and unnatural ("brother" -> "older brother or younger brother," "ao" -> "blue or green," e.g.), and may lead the listener to think the original speaker was being unnecessarily coy, evasive or imprecise. "Doesn't she know whether her own brother is younger or older than she is? Or is there some reason she doesn't want us to know...?" "Is he color-blind? Why can't he just tell us what color it is? Did he really see it?" Etc.

In any case, either language can be used to be as precise or ambiguous as the speaker wishes.

I know it can be frustrating, but it is probably less ulcer-generating to let minor apparent oddities in translation go.

 

[rowmag]

Welcome to you.

You could be right. On the sign a few lines under the 12 mSv/h header another measurement - 950 mSv/h -- is written in smaller types,

Great Madderdoc, so maybe Tepco reported the picture of the 950 mSv/h rubble I admit... for those who has good eyes at least I guess Almost 1 Sv/h could explain grass death.

Could somebody translate the full text for information?

Much of it is too fuzzy to read, but:

"The dose equivalent rate in this area is

12 mSv/h

Don't carelessly approach

(<illegible> dose equivalent rate: as high as 950 mSv/h)"

Followed by date and time (4 June 2011 at 10:00) and signature info.

 

[westfield]

NHK has a recent video of various shots from around the site:
http://www3.nhk.or.jp/daily/english/05_06.html
The shot of the putzmeister looks like it has the dangling instruments at #4.

Of course it's good to have more images and video but I can't be the only one that has been watching these and thinking that we only get the "amateur" footage and somewhere, someone has been shooting proper video. Hopefully one day we will be able to see what TEPCO have been seeing.

 

[westfield]

snip >

I wonder if the Japanese language might even be worse in that regard. Even some of the so-called "perfect" translations we've seen of some reports seem to suffer from the same imprecision and lack of consistency. But I'm not a linguist, so who knows.

I have Japanese family and one thing I have noticed is you can ask three different native Japanese speakers that all have excellent english language proficiency to translate a simple Japanese sentence and you will often get three quite different translations. Just from one simple sentence. Not every time but often. When it comes to engineering translations it could only get more tricky. It is probably too much to expect a universal "perfect" translation, you will get interpretations, not direct translations of Japanese. On top of that are the levels of respect that require varying words & grammar in Japanese. Some writers will be more traditional and others not so much. Further, on a personal level at least, I have learned to try and "hear" what is NOT being said in Japanese conversations which can be more interesting, revealing and\or important than what is actually uttered.

Personally, I never take translated Japanese at face value, I expect it to be incorrect, possibly the opposite of what was initially said unitl I can see two or three other translations of the same to compare.

Plenty of things I have tried to machine translate have ended up appearing to be quote from a pathologically lying yoda compared to what was actually said ;) Be very cautious.

 

[MiceAndMen]

They have already backed off from this theory:

http://www.asahi.com/special/10005/TKY201106040552.html

They realized there is another valve in the system which should have closed automatically when power was lost.

Oh my. It's not easy keeping up with all the revised accounts and stories.

The original Japanese suggests (to me) that the lesson learned from Chernobyl was a general one about putting more thought into preparing for severe accident scenarios, not necessarily the specific one about hydrogen vents:

http://www.asahi.com/special/10005/TKY201106030574.html

To me it still seems like an awful non sequiter. The way it is written there in English strongly implies a cause-and-effect relationship between the two events, but I will happily defer to your judgement since I don't know any Japanese beyond a few cooking terms picked up from watching Iron Chef.

In any case, either language can be used to be as precise or ambiguous as the speaker wishes.

I snipped out much of what you wrote, but thank you for that. Most interesting; the part about blue and green is fascinating, really. I'm in total agreement that all languages probably have their idiosyncracies and ambiguities. At one time I considered myself fluent in French. I even won a few statewide awards when I was in high school. The pinnacle of my achievement in that language was when I once fooled a taxicab driver in Paris about where I was from. I could probably still get by, but many years of disuse have atrophied my vocabulary and pronunciation.

It helps a great deal to have people on this forum who can actually read, write and speak Japanese, and I thank you for all your contributions so far!

 

[GJBRKS]

The heat decays at an exponential rate.

http://en.wikipedia.org/wiki/Decay_heat#Power_reactors_in_shutdown

(t)

Your graph extends to 10 days .

here's data for one year :

http://mitnse.com/2011/03/16/what-is-decay-heat/

 

[MadderDoc]

New analysis introduced on the front page of today's Tokyo Shimbun puts the disparity between explosions in reactor buildings one and three down to the concentration and of hydrogen - 15% in building 1 one vs 30% in building 3:

http://tinyimage.net/images/54067954849412280308_thumb.jpg

Sorry I don't have a scanner available today.

The headline reads: 「Reactor number 3's explosion was a "detonation"」

The graphic shows hydrogen @ 15% in building one combusting over 'several seconds' vs hydrogen @ 30% detonating in '0.02 seconds' in building 3.

I wonder who the author of the analysis is, certainly it is an interesting result. Does the article say anything about the observations on which the the analysis is based, and the thoughts that have given them order?

 

[Hiyodori]

I wonder who the author of the analysis is, certainly it is an interesting result. Does the article say anything about the observations on which the the analysis is based, and the thoughts that have given them order?

The article is available online here:
http://www.tokyo-np.co.jp/article/feature/nucerror/list/CK2011060602100004.html

Analysis done by the "Institute of Applied Energy" (http://www.iae.or.jp/)

 

[jlduh]

Updated my plots of Fukushima daiichi reactor parameters up to NISA release 159 (jun/04 15:30)
http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/plots/cur/Main.html

I have also added some temperature data for late march taken from the TEPCO files
http://www.tepco.co.jp/nu/fukushima-np/f1/images/syusei_temp_data_1u.pdf
http://www.tepco.co.jp/nu/fukushima-np/f1/images/syusei_temp_data_2u.pdf
http://www.tepco.co.jp/nu/fukushima-np/f1/images/syusei_temp_data_3u.pdf
Unfortunately these files do not give much new data besides what i already had,
at least for that time frame. They seem to confirm that something exceptional happened to reactor #3
in the early hours of march/21, just before the black smoke event. (Thus that
black smoke does not seem to be just an ordinary chemical fire.)

Between NISA releases 158 and 159 the core presures of reactor #1 have abruptly fallen from 679 kPa and 1674 kPa to 126 kPa and 101 kPa (?), respectively:
http://www.ic.unicamp.br/~stolfi/EXPORT/projects/fukushima/plots/cur/out/plot-pres-un1-t-T-full.png
Since the other variables remained stable, it may be a transcription error (today is sunday; only a lowly trainee in the office, perhaps?), or they recalibrated the instruments and found that the previous readings were garbage.

As you talk about the event around March 20/21, I just want to cross link with this post in the "contamination thread":

https://www.physicsforums.com/showpost.php?p=3340132&postcount=43

See the table with data it seems from CTBTO measurement network, but as i don't speak japanese i cannot give precisions of where it was measured, i just read the numbers for the various isotopes!

http://www.cpdnp.jp/pdf/110603Takasaki_report_May30.pdf

But this is interesting as you can see that there has been three spikes in the measurements:

- One (the biggest) between March 15 and 16
- One between March 20 and 21 (which fits the "black smoke coming from N°3" period)
- One between March 29 and 30

 

[jlduh]

Agree with more sand added as the sand melts and mixes with the Corium, that worked in Chernobyl, we should not experiment here, same stuff as was mixed in Chernobyl... And, absolutely NO water...

There is IMO a major difference between Chernobyl and Fukushima, as Chernobyl core and even graphite in fire was totally exposed after the explosion, so it could be reached by dropping lead and sand from helicopters; whereas in this case the cores are under or inside steel and concrete structures. As I said, this is in a sense better because it increases the shielding from direct radiation BUT on the other hand I don't see how you could get access to hot spots with sand?

Sand needs for melting very high temps, It will melt if in contact with hot fuel/corium, but at Fukushima, how to you send the sand where the cores are (we don't even know where they are...)?

Water is a dangerous poison in the mid/long term because it carries out a lot of contamination that I think very quickly they won't be able to handle anymore once the basements will be full.

But I'm afraid it was the only material that could get access to the cores inside this mess.

 

[tsutsuji]

The article is available online here:
http://www.tokyo-np.co.jp/article/feature/nucerror/list/CK2011060602100004.html

Thank you for the link.

Let's extract a few more information :

The Institute made a computer simulation.

540 kg of hydrogen had been produced at unit 3 and 270 kg at unit 1.

The pressure at unit 3 was 60 atmospheres.

Masanori Naito (Institute of Applied Energy) says that the bending out of shapes of the steel frame at unit 3 or the fact that the debris of unit 1 fell close to the building fit the results of the study.

Atsumi Miyake (Yokohama National University) says that beyond the hydrogen concentration, the detonation depends also on the airtightness and the energy added when burning, all things that will greatly influence the design of nuclear power plants in the future.

 

[Jim Lagerfeld]

I wonder who the author of the analysis is, certainly it is an interesting result. Does the article say anything about the observations on which the the analysis is based, and the thoughts that have given them order?

For what it's worth, here is my effort at a quick translation of the online version. I'm not fluent, and my major is in media studies rather than atomic physics. So with those caveats:

Reactor number 3's explosion was a "detonation"

According to analysis released by Institute of Applied Energy (based in Tokyo's harbor ward ), the hydrogen explosion which occurred at reactor number 3 of TEPCO's Fukushima Dai-ichi nuclear power plant created a shockwave which exceeded the speed of sound, a phenomenon known as a "detonation". This means that due to a difference in hydrogen concentrations present at the time, the explosive force exceeded that of reactor 1.

The explosion at reactor three released a plume of sooty smoke 300 meters into the air, which took on the appearance of a mushroom cloud. This caused speculation regarding a possible nuclear explosion to circulate amongst some foreign media outlets. When compared to the explosion at reactor one - which appeared as a white colored cloud of smoke which erupted laterally - the explosion at number three seems to have occurred on a much larger scale. On receipt of software simulations developed by the Minister of Trade and Enterprise, the IAE undertook to analyze the processes behind the hydrogen explosion.

At 2.40am the 13th of March, the supply of coolant water to the fuel rods was interrupted. This led to the heating of the water inside the reactor producing steam, which caused a chemical reaction with the fuel rods' Zirconium alloy cladding, in turn producing large amounts of hydrogen.

Hydrogen explodes on reaction with oxygen, and if concentrations of hydrogen in the atmosphere exceed 18%, the 'detonation' phenomenon becomes more likely. Ultimately 540 kilograms of hydrogen were produced at the number three reactor. Approximately thirty two hours after cooling was interrupted, the concentration of hydrogen accumulated the top floor of the reactor building approached 30% and at about 11.01am on the 14th of March the detonation occurred. The combustion occurred within 0.02 seconds, creating approximately 60 atmospheres of pressure inside the building, blasting the upper portion of the building into the air.

On the other hand, the explosion at reactor one occurred about 24 hours after cooling was interrupted, whilst the reactor also contained fewer fuel rods than the larger number three reactor. Two hundred and seventy kilograms of hydrogen were produced, around half the amount in reactor number three, limiting the hydrogen concentration in the upper floor of the reactor building to around 15%. Accordingly, the hydrogen combusted over several seconds without causing a detonation, destroying the walls of the building and causing the smoke to escape the building.

IAE chief Mr Masanori Naito stated that "the steel frame of the number three reactor building appears to have been warped and distorted, confirming the destructive power of the detonation. Aerial photographs of the number one reactor building show rubble from the walls of the building was strewn close to the building, further supporting the results of our analysis".

Large influence on future designs

According to professor Atsumi Mitake from the Yokohama National University School of Engineering, the possibility of a detonation occurring depends not only on the concentration of gasses, but is also determined by the airtightness of the enclosed space and the energy of the ignition source. If it is to be understood that a detonation occurred, then this will exert an exceedingly strong influence on the planning of future nuclear projects.​

 

[tsutsuji]

and the energy of the ignition source

I think that what Miyake (not Mitake) is saying, although it is not very clear, is that you must calculate the energy added by the burning of materials other than hydrogen that are present in the building.

On June 4th, NISA approved to store more contaminated water from unit 2 into the process main building of the waste treatment facility. Contaminated water will be added until the OP+4200 mm level (below the "run through" part in the 1st basement ; this is still lower than the ground water level), is reached (instead of the previous OP+3700 mm : filling of the 2nd basement only), and the storing capacity will reach 11,500 m^3 (instead of 10,000 m^3) : http://www.meti.go.jp/press/2011/06/20110604003/20110604003.html (includes request letter from Tepco and reply letter from NISA)

The process main building had been filled up to OP+4138 as of June 6th 7:00 JST : http://www.tepco.co.jp/nu/fukushima-np/images/handouts_110606_01-j.pdf

 

[joewein]

It was reported that there were 32 MOX fuel assemblies in Unit 3, or about 6% of the core of 548 assemblies. They were operating in their first cycle, so they didn't have much operation/exposure. Ostensibly, the MOX fuel was derived from spent fuel from the Fukushima reactors, thus it was reactor grade, and the Pu isotopics would have reflected that legacy. The MOX fuel would be designed to match the enrichment of the U-235 assemblies, which is about 4% U-235. So likely the MOX would be about 6% Pu, with a mix of Pu239, 240, 241 and 242.

Spent fuel contains Pu isotopes. The use of MOX is rather insubstantial to the event and the current state of Unit 3.

I agree, this problem is largely overestimated. Most non-technical observers are unaware of the plutonium levels in burnt up fuel rods. I recall from literature about reprocessing plants that about 1% Pu (produced through neutron capture from U238) remains in waste from LWR fuel initially enriched to 5% U235.

Unit 1 and unit 6 used fuel enriched to 3.4% U235, unit 2-5 to 3.6% U235. If in fully burnt up fuel the equivalent of 1/5 of the U235 fuel stays behind as unfissioned Pu, that would be about 0.7% by weight in those BWRs. Assuming the fuel was on average half burnt up at the time of the accident, as it is replaced in portions (1/3 at a time?), let's make that 0.35% of the total.

In the MOX reactor, in 6% of fuel rods 6% by weight would be plutonium when starting it up again. That's about 0.36%, on top of the Pu in spent uranium rods (94% of the rods).

While the MOX scenario means an increase of plutonium in the core compared to enriched uranium fuel (maybe a doubling at the worst case), some media reports make it sound like Pu was a new worry created through the use of MOX fuel, which it definitely is not. Units 1 and 2 collectively may well contain more plutonium that does unit 3.

 

[jlduh]

I appreciate the mistrust/distrust of the nuclear industry. The event at Fukushima has betrayed whatever trust had been established.

I appreciate that you honestly recognize this. And to continue on this subject (but moving on the more political thread), I think one of the root causes of this distrust situation is maybe summarized in this message i just posted, based on a declaration of the chairperson of Japan's Nuclear Safety Commission, Haruki Madarame:

https://www.physicsforums.com/showpost.php?p=3341445&postcount=284

 

[zapperzero]

http://mdn.mainichi.jp/mdnnews/news/20110606p2a00m0na009000c.html

Airborne contamination estimates revised upwards by NISA "from 370,000 terabecquerels to 850,000 terabecquerels", counting from the start of the accidents to April 5.

 

[clancy688]

http://mdn.mainichi.jp/mdnnews/news/20110606p2a00m0na009000c.html

Airborne contamination estimates revised upwards by NISA "from 370,000 terabecquerels to 850,000 terabecquerels", counting from the start of the accidents to April 5 (yesterday).

Now it's 20% Chernobyl...