Japan Earthquake: nuclear plants

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Thank you both for your responses. Very helpful. Yes I was wondering what the likely state of any fuel mass were at this time, considering the degradation of the fuel, the constant immersion in water, and the passage of two years. Part 2 of my question is as Rive mentioned; is the purpose of the continuous flow of water to stop the fuel mass from re-heating into a molten state?

Given the problems created by the daily input of a hundred or so tons of water, at what time will it be prudent to begin reducing the volume of water? My only reference is Chernobyl, and from what I gather, the fuel ceased to be a moving mass fairly early on, and without the addition of so much water as in the case with Fukushima.

So my guess (validated by Rive above) is that the fuel at Fukushima has traveled a shorter distance, indeed may to a significant degree remain inside the RPVs, and therefore has far fewer impurities (concrete, steel, etc...) than what was at Chernobyl, and therefore the decay heat is still high enough to reach the point where it would re-melt were the heat not being continually removed.

This is just a mental exercise; something to think about while reading all the alarmist stuff about china syndromes, which is something I think Arnie Gundersen claimed recently. And there is a lot of nonsense about "where are the cores", which seems to me to be a ridiculous question, and yet one sees it from time to time on certain sites.
 
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... and therefore the decay heat is still high enough to reach the point where it would re-melt were the heat not being continually removed.
... and therefore it cannot be ruled out that the decay heat is still high enough that some parts might re-melt...

I think it's also unlikely that it would re-melt at large scale. But I cannot tell... Maybe somebody else can. I don't know.

Anyway, they will keep the cooling and will keep the temperature as it's required to keep the 'cold shutdown'.


About Gundersen... I cannot recall: was there any of his claims ever be proven right later on?
 
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I read, I can not remember where, but it's Japanese sources,
for physical calculations of residual heat
that water can be turned off in 2018.

In addition, in the Chernobyl sarcophagus fuel mass to be at high embrittlement.
Have the fuel dust (30-50 tone as the Chernobyl) is worse than having a fuel slush.
 
Given the problems created by the daily input of a hundred or so tons of water, at what time will it be prudent to begin reducing the volume of water? My only reference is Chernobyl, and from what I gather, the fuel ceased to be a moving mass fairly early on, and without the addition of so much water as in the case with Fukushima.
My guess is: TEPCO continues to pour water based largely on paranoia and fear of bad PR. If they stop, fear-mongering idiots from all sides would scream bloody murder.

So my guess (validated by Rive above) is that the fuel at Fukushima has traveled a shorter distance, indeed may to a significant degree remain inside the RPVs, and therefore has far fewer impurities (concrete, steel, etc...) than what was at Chernobyl, and therefore the decay heat is still high enough to reach the point where it would re-melt were the heat not being continually removed.
Total decay heat does not decrease from impurities.

By now, most of decay heat comes from Sr-90, Cs-137, Cs-134. Cs is water soluble, a lot of it had been leached out.
 
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My guess is: TEPCO continues to pour water based largely on paranoia and fear of bad PR. If they stop, fear-mongering idiots from all sides would scream bloody murder.
I'm getting really really tired of this attitude of yours. A back-of-napkin calculation would show that the corium still needs cooling, especially if it is (as TEPCO assumes) mostly in one piece.

Think you can do better? Fine. Do the work, show the work and THEN call me and a.ua. and others here "fear-mongering idiots". Not before.
 
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I read, I can not remember where, but it's Japanese sources,
for physical calculations of residual heat
that water can be turned off in 2018
It's Tsutsuji-san translated.:smile:

10) Use of PCV fuel debris air-cooling
At present, heat removal of the fuel debris contained in units 1,2,3 reactors and PCVs is done by water cooling by water injection. but in the future, as decay heat diminishes, it is possible to reduce the generation of contaminated water by shifting from water cooling to air cooling.
As additional generation of contaminated water is annulled, contamination reduction can be expected in the buildings where flowing presently occurs (turbine buildings, etc.).

Problems/feasibility:
Securing wind ventilation method;
- For the time being, as the decay heat is high, considerable ventilation power is needed (with the present decay heat, installation is difficult).
- At the earliest, decay heat is expected to become smaller by 2018, but further study is needed so that the air is uniformly blown onto the fuel debris.
Responding to the situation while the fuel is being removed;
- If the PCV has to be filled with water for the purpose of fuel removal, it means that contaminated water has to eventually be generated again, even if temporary air-cooling could be achieved
 
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Continuing the theme of a former fuel.
Here you can see the continuation of the Japanese

Units[/PLAIN] [Broken] 1 and 2 and the torus chamber of accumulated water
For analysis of the precipitate


nikkkom
By now, most of decay heat comes from Sr-90, Cs-137, Cs-134. Cs is water soluble, a lot of it had been leached out
It seems to me, the alpha decay generates more heat.
RTG, RITEG
It should produce high energy radiation. Energy release per decay is proportional to power production per mole. Alpha decays in general release about 10 times as much energy as the beta decay of strontium-90 or cesium-137.
All analyzes indicate a low level of alpha nuclides in the "dirty" water
Perhaps the fuel matrix retains the bulk of plutonium and other alpha nuclides.
So it is necessary a long time to cool ...
 
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So my guess (validated by Rive above) is that the fuel at Fukushima has traveled a shorter distance, indeed may to a significant degree remain inside the RPVs,
No. Recent simulations show almost complete cores of 1, 2 and 3 are ex-vessel.

and therefore has far fewer impurities (concrete, steel, etc...) than what was at Chernobyl, and therefore the decay heat is still high enough to reach the point where it would re-melt were the heat not being continually removed.
This is neither here nor there. If the corium has dropped out as simulations show, it has mixed with concrete from the basemat until a sort of thermal equilibrium was reached. It doesn't look anything like Chernobyl, probably. Certainly it has mixed with all the steel in the core and with whatever it found on the bottom of the RPV - mostly the actuators for moderator rods.

And there is a lot of nonsense about "where are the cores", which seems to me to be a ridiculous question
There is almost no doubt they are under the RPVs (although we can't exclude some melt flowing into a torus, I think?).

A better question would be "what shape are the coriums in?". Could be debris bed like at TMI. Could be splatter as if from a big sieve, could be just a big blob or even "lava tubes" or other exotic things we haven't thought of. The answer to this question will come with new remote explorations, I hope.
 
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Recent simulations show almost complete cores of 1, 2 and 3 are ex-vessel.
Could you please link me the latest simulation you know about? The one I know about is a bit old. It shows that U1 core is completely ex-vessel, but for U2 and U3 the result is in the edge of in-vessel and partially ex-vessel.
 
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If the corium has dropped out as simulations show, it has mixed with concrete from the basemat until a sort of thermal equilibrium was reached. It doesn't look anything like Chernobyl, probably.
If any of the fuel masses have reached thermal equilibrium, it begs the question of why water continues to be poured onto them. I mean, if the heat needs to be removed otherwise the fuel will re-melt, you can't really call it equilibrium can you? Or, are you saying it has reached equilibrium, its just that the equilibrium temperature is so high that it will still melt steel and concrete?
 
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If any of the fuel masses have reached thermal equilibrium, it begs the question of why water continues to be poured onto them. I mean, if the heat needs to be removed otherwise the fuel will re-melt, you can't really call it equilibrium can you? Or, are you saying it has reached equilibrium, its just that the equilibrium temperature is so high that it will still melt steel and concrete?
I am sorry, I was not using equilibrium in the strict sense of "no heat flow across the boundary". I see how this can cause problems. It's only balanced in that the temperature is constant - as long as there's water flowing through.
 
Speaking about ORNL study, eight hours after the Fukushima Daiichi Blackout Station, corium (molten fuel) may have melted through RPV then through the containment 7 hours later; that is the full melthrough sequence might be as short as 15 hours timeframe.

Same reactor (Browns Ferry 1 unit), same accident (Blackout Station).

http://web.ornl.gov/info/reports/1981/3445600211884.pdf [Broken]

Picture is from p. 133 "vertical concrete penetration".
 

Attachments

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http://www.epri.com/abstracts/Pages/ProductAbstract.aspx?ProductId=000000000001025750
claims full meltdowns for all three, but you are right, it does not claim specifically that 2 and 3 are ex-vessel

In particular, it states for unit 3:
The types of pressurization transients observed in the 1F3
drywell following RPV depressurization require the addition of energy. This could be
through a relatively rapid but brief dissipation of some of the stored energy in the core debris
or through chemical reactions (for example, oxidation). The simulation of severely degraded
HPCI injection rates at low RPV pressure indicates that one way to generate this type of RPV
pressure transient is through ex-vessel relocation of core debris. However, several
uncertainties related to in-vessel core degradation in a BWR and the impact of salt water on
the core degradation process still remain.
but concludes

The core is
likely significantly damaged and has either relocated almost entirely into the RPV lower plenum
or relocated ex-vessel. These are both reasonable damage conditions based on the available
information.
For unit 2 a core temp progression analysis (indicating complete meltdown at 95 hours) starts on page 220 but there is indeed no mention of ex-vessel.

Oh well. I should learn not to rely on my memory. At all.

EDIT: I can't find this:
MELCOR Simulations of the Severe Accident at the Fukushima 1F2 Reactor
http://www.osti.gov/scitech/biblio/1064358
halp?
 
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Getting close

http://info.ornl.gov/sites/publications/files/Pub37640.pdf [Broken]
hmmm

Using the water injection estimate information by TEPCO, simulations [9,10] generally predict limited core degradation that is later quenched in-vessel. However, the amount of water that made its way to the core region remains a key uncertainty. Decreasing the water injection by half resulted in large-scale core relocation before the end of the simulation. If that simulation were extended, failure of the lower head and melt relocation would likely be predicted
 
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EDIT: I can't find this:
MELCOR Simulations of the Severe Accident at the Fukushima 1F2 Reactor
http://www.osti.gov/scitech/biblio/1064358
halp?
No luck for me, too.

Here is a document which is older but has the same person as co-writer:
http://melcor.sandia.gov/docs/Fukushima_SAND_Report_final.pdf

IMHO we won't be able to reach conclusion. Some documents suggests, that for U2 and U3 the actual core status heavily depend on the water amount pumped in by fire trucks: but that water amount will remain unknown.

We have to wait for the next bunch of borescope missions.
 
nikkkom

It seems to me, the alpha decay generates more heat.
Fission fragments are almost exclusively beta and gamma emitters.
Alpha emitters are uranium and transuranics. They are minority contributors to decay heat at this point.
 
I'm getting really really tired of this attitude of yours. A back-of-napkin calculation would show that the corium still needs cooling, especially if it is (as TEPCO assumes) mostly in one piece.

Think you can do better? Fine. Do the work, show the work and THEN call me and a.ua. and others here "fear-mongering idiots". Not before.
"After one year, typical spent nuclear fuel generates about 10 kW of decay heat per tonne, decreasing to about 1 kW/t after ten years."

Considering leaching of Cs, let's assume than by now (almost 2.5 years after disaster), every ton of fuel generates 4 kW. Then ~100 tons of fuel in RPV/PCV generate 400 kW. This power can evaporate about 13 tons of water in one day, if no power is lost to ambient.
 
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So what is your conclusion, nikkkom? Does the corium still need water cooling?
 
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