Japan Earthquake: Nuclear Plants at Fukushima Daiichi

[turi]

What or whom does SFP 1 need to be shielded from?

Judging from the radiation readings that have been released recently, it appears that no human will be working anywhere near that SFP for the next 150 years or so.

The rods in unit one are putting out about 2% of the heat and radiation that the #4 pond was said to be producing early on.
I can't say what would be the result of those particular rods meeting air but if it were a problem it would be easy enough to fill the pool with sand.
[...]

The rods would melt and release various volatile radioactive isotopes into the air. Why would you want that? Just so you don't have to care about the SFP 1 anymore?

 

[SteveElbows]

Finally:
-From 10:16 am to 10:48 am on June 5, we started the water
injection to the spent fuel pool of Unit 1 by a temporary motor
driven pump.

Japanese version of status updates said that they injected just 15t. This is very small amount compared to what goes into reactor 4 pool, and is further indication that unit 1 pool is not a major concern at this time.

 

[inkling01]

Yes, it is like a revolver pointed to Mother Earth with only one bullet loaded, but we don't know whether it will fire or not. I hate those who did this to us. I don't like being forced to play Russian Roulette with my family and friends...

I hope you don't mind, but I sent you a PM

 

[Bioengineer01]

Well, I share all your views, you avoided me to write it!

To tell you the truth, if i posted this image at first with the comments I did, it was because I also share as a possibility the fact that this picture has been "arranged" for communication purposes, especially when you discover that in parallel, as you said, in the last map before this one (28 may), these VERY VERY VERY VERY high dose rubble (if I want to compare with this "high dose rubble of 12 mSv/h! ) of 950 and 550 mSv/h were not reported!

So basically they find 550 and 950 mSv/h rubble, and they communicate with a "nice" picture of a "high dose rubble" of 12 mSv/h? Guys, if they put a cone on every little bit of concrete like this one (the red one) with 12mSv/h or more, i can tell you that the all plant is going to be flooded with cones in addition to water...

Hahahahaha...Very good one

 

[Quim]

eventually access the reactors and cores of Units 1, 2 and 3

Possibly you industry guys need to pause and take a deep breath. Nobody is going to "access the reactors and cores of Units 1, 2 and 3" in the lifetime of you or your grandchildren.

There are no more "reactors" or "cores" in units 1,2 or 3.
There are blobs of corium which hopefully, but not necessarily, live mostly in what is left of the primary containment vessels. These blobs should not be dug up in any way.

 

[Bioengineer01]

They don't post pictures - it is wrong.

They post pictures - it is wrong.

I think you are trying to make way too much from random facts. And it is not something that fits this thread.

Sorry Mentor, you probably know a lot more physics than me, but I did work in a F50 Corporation, they have FULL departments of people that all they do all day long is to discuss details of how to arrange pictures like this to achieve the communications goal that they have. Nothing they report is random, unless you can get your hands on raw data that sometimes leaks out form a whistle blower that doesn't want to be identified. A 6 billion top line corp. in the USA may have 100+ people working on communications...

 

[Bioengineer01]

Do you honestly think that Arny Gundersen is painting an inaccurate tapestry? If so, please paint me an accurate one, and give me links to get accurate information.

Andy, you can get a much better picture of the consequences of radiation from Dr. Helen Caldicott, here is her web site: http://www.helencaldicott.com/ she was a high income high prestige MD, that delved into the effects of radiation on health and decided to make it her life goal to fight those who were spreading lies and creating cover ups. I call her the Mother Theresa of radiation protection. Of course the Nuclear industry calls her nuts. But never ever dears to engage her on a serious scientific discussion on the matter.

 

[elektrownik]

http://www3.nhk.or.jp/daily/english/05_21.html"

 

[Quim]

The rods would melt and release various volatile radioactive isotopes into the air. Why would you want that? Just so you don't have to care about the SFP 1 anymore?

I don't agree with your scenario.

 

[radio_guy]

Possibly you industry guys need to pause and take a deep breath. Nobody is going to "access the reactors and cores of Units 1, 2 and 3" in the lifetime of you or your grandchildren.

There are no more "reactors" or "cores" in units 1,2 or 3.
There are blobs of corium which hopefully, but not necessarily, live mostly in what is left of the primary containment vessels. These blobs should not be dug up in any way.

Cleanup for the 50%? melted core at TMI took 5 years..
http://www.threemileisland.org/downloads//226.pdf

I have a feeling it won't take generations and generations to cleanup the majority of this mess. but the site will never be 100% again.

 

[Quim]

Cleanup for the 50%? melted core at TMI took 5 years..

I have a feeling it won't take generations and generations to cleanup the majority of this mess. but the site will never be 100% again.

Each of the situations at #s 1,2 and 3 are far worse than TMI.

The way I see it, although the site around the containment structures can and should be cleaned up, the corium blobs themselves should not be disturbed.

There is nothing to be gained from mucking about with the corium.

 

[radio_guy]

Each of the situations at #s 1,2 and 3 are far worse than TMI.

The way I see it, although the site around the containment structures can and should be cleaned up, the corium blobs themselves should not be disturbed.

There is nothing to be gained from mucking about with the corium.

I find it hard to just assume the fuel is in a solid blob melting away, it could be all broken up in bits, shattered when the cold seawater hit it, it could be in multiple blobs.. i can envision a few of these scenarios.

They will make plans about what they can and cannot do once they are able to see what they are dealing with, right now it's just all assumptions and I feel it's a bad call to base what their future actions will be on that.

otherwise, can you point me in the direction of some solid proof that the core is in one solid blob in the bottom of the building? I would like to see it, bet it looks cool.

 

[Bioengineer01]

Peta is 10^15, rather than 10^18, at least afaik.

You are correct, THANKS! I'll edit the post.

 

[Bioengineer01]

Yep. Isn't it a great feeling when you find that you have been plotting and analyzing garbage data for three months?

So, to simplify the picture, all three reactors are at atmospheric pressure. So they probably have a hole at the bottom, and their fuel is lying on the concrete at the bottom of the drywell, optimistically. And their "primary containments" seem to be leaking like sieves.

(But how could a manometer measure 1.6 MPa if everything is at atmospheric pressure? Perhaps a steam leak from Fukushima Daini, traveling through a crack in the Earth's mantle?)
Thanks. I wasn't sure what exactly was the bottom of the instrument's scale and conservatively guessed -4 m.

(They could make our life a bit easier by writing "< 5000mm", "> 400 C" etc. instead of just "downscale" or "offscale"...)

I can't make the sudden increases in temperature in Unit 3 RPV compatible in my mind with a complete meltdown and a hole in the bottom of the RPV ... Comments?

 

[Bioengineer01]

http://www3.nhk.or.jp/daily/english/05_21.html"

Your link didn't work, here is the corrected one that hopefully will work:

http://www3.nhk.or.jp/daily/english/05_21.html

 

[dh87]

Hi to all.
I run a rapid back of the envelope calculation on the CS137 quantity TEPCO estimated.

If I got it right from Wolfram Alpha the activity of CS137 is 3.214 TeraBq/gram.

Having TEPCO estimated overall CS137 at 720,000 TeraBq, that would lead to 720,000/3.214=224,020 grams of CS137.

I then tried to understand in what relation that value is in respect to the total CS137 inventory that can be expeced from 1,2,3 cores.

I know this has been much more accurately estimated somewhere before in this 3d but I unfortunately do not have the possibility of searching the whole discussion right now.

However from wiki I got a fission yield of 6.0899% for CS137. That yield together with the mass ratio of U235 vs CS137 leads me to estimate in about 6.26 tonns the amount of U235 that has to undergo fission to pruduce this amount of CS137 (224,020/0.060899*235/137 grams).

Now if I remeber correctly at 32% of thermal efficiency 1 tonn of U235 has to undergo fission to produce 1 Gigawatt for one year.

Being almost exactly 2 gigawatts the overall power output of the concerned units, it would seem that the estimated CS137 already in the water is in the order of magnitude of 3 yrs worth of fission process.

In other words that would lead me to think that this estimates means that much of the molten fuel is already soluted in water.
On the other hand this conclusion, in a way reassuring, seems unreaalistic to me.

what I am I doing wrong ?
what do you think ?
thanks in advance

I think that the 720,000 TBq is just in the water. There's also a significant airborne release of Cs. I can't find the numbers at the moment. I think that a lot of the radioactive Cs and Sr may not be in the cores any more, as I tried to say in post #8701 (https://www.physicsforums.com/showpost.php?p=3336116&postcount=8701).

Edit: An estimate for airborne Cs-137 release is only 10,000 TBq, on p. 20 of this document: http://www.tepco.co.jp/en/nu/fukushima-np/f1/images/f12np-gaiyou_e.pdf. So, the Cs-137 in the water appears to be the major release.

 

[jim hardy]

jorge stolfi

i want to personally extend thanks to you for your work in making hose graphs.

curious, whatever happened to 3 on 21st accompanied high water injection through "fire line"?
i don't know what fire line is - does it go into vessel(core spray perhaps) or does it spray down the drywell?

Do you think drywell got hot enough to burn cable insulation and jet pump oil reservoirs?

Is there a BWR guy in the house?

 

[Astronuc]

Possibly you industry guys need to pause and take a deep breath. Nobody is going to "access the reactors and cores of Units 1, 2 and 3" in the lifetime of you or your grandchildren.

There are no more "reactors" or "cores" in units 1,2 or 3.
There are blobs of corium which hopefully, but not necessarily, live mostly in what is left of the primary containment vessels. These blobs should not be dug up in any way.

Not necessarily so. One has no evidence of 'blobs of corium'. Any reference to corium is speculation.

Those outside of industry have little credibility regarding the state of the reactor/core/fuel.

There is an appropriate engineering solution, but it is unlikely to come from outside the industry.

 

[Bioengineer01]

Arnie Gundersen said:
"Well, I am in touch with some scientists now who have been monitoring the air on the West Coast and in Seattle for instance, in April, the average person in Seattle breathed in 10 hot particles a day"

http://www.chrismartenson.com/martensonr...on-worsens

Auch...

 

[Astronuc]

http://www3.nhk.or.jp/daily/english/05_21.html"

From the article -

The samples of plutonium-239 and 240 make up a total of 0.078 becquerels per kilogram.

This is close to the amount produced by past atomic bomb tests.

Even 1 Bq/kg is low. One would need to compare the concentration of Pu isotopes with comparable values from other regions and areas away from NPPs in order to discern the significance of the reported values.

 

[StrangeBeauty]

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.

 

[SteveElbows]

I can't make the sudden increases in temperature in Unit 3 RPV compatible in my mind with a complete meltdown and a hole in the bottom of the RPV ... Comments?

Well I agree in so much as I have trouble making this temperature stuff compatible with the idea that the entire core has left the RPV. I am keeping an open mind in regards the spectrum of possibilities, but certainly the variety of temperature data from reactor 3 keeps many of the extreme reactor 3 possibilities somewhat beyond the realms of likely fact.

But even if the temp data is fairly accurate, I can still picture quite bad core damage, some holes and a certain amount of core material possibly escaping. This is not the same as the conclusion some people are keen to reach, that the core is sitting on the drywell floor, which for me remains a possibility, but one that is far from proven. It does not help that drywell temperature data is not collected in abundance.

 

[SteveElbows]

Each of the situations at #s 1,2 and 3 are far worse than TMI.

The way I see it, although the site around the containment structures can and should be cleaned up, the corium blobs themselves should not be disturbed.

There is nothing to be gained from mucking about with the corium.

Thats a judgement that needs not be made right now. For a good while the focus will be on site cleanup, dealing with radioactive water, and trying to get the wrecked-reactor equivalent of cold-shutdown.

The decision of whether to mess around with the cores at some future point is down to risk & reward analysis that can be done at the time. Sure the industry would like to be able to show the world that they can do a good job of handling this stuff, but they are unlikely to attempt it if the risk of causing further problems is too high, because those new problems would be bad PR and are not worth it. Rather, the sane parameters that could tip this decision one way or another are all about containment. If the risk of core material escaping into environment by leaving it alone is greater than the risk that comes with doing something to deal with it more substantially, and there is some practical method they can actually apply to deal with it, then they will be correct to muck about with the corium, not reckless.

 

[elektrownik]

Unfortunately, after they discover that two water sensors and two pressure sensors in unit 1 were wrong we can't trust any data

 

[Quim]

Thats a judgement that needs not be made right now. For a good while the focus will be on site cleanup, dealing with radioactive water...

I am suggesting that the best thing to do right now is to stop pouring water into the nuclide pile. Until the water flow out of the high radiation area is halted, we remain in the expansion of the problem mode, not the cleanup mode.

trying to get the wrecked-reactor equivalent of cold-shutdown.

Can you describe that?

 

[Bioengineer01]

I am suggesting that the best thing to do right now is to stop pouring water into the nuclide pile. Until the water flow out of the high radiation area is halted, we remain in the expansion of the problem mode, not the cleanup mode.



Can you describe that?

Hahahaha, sorry guys, but you made me laugh, thankfull for that, there is no way in hell that you can get a molten pile of corium into cold shutdown, not even the equivalent of it... Hahahaha

 

[turi]

Hahahaha, sorry guys, but you made me laugh, thankfull for that, there is no way in hell that you can get a molten pile of corium into cold shutdown, not even the equivalent of it... Hahahaha

The equivalent would be having it submerged in water and keeping the water below boling point.

 

[SteveElbows]

I am suggesting that the best thing to do right now is to stop pouring water into the nuclide pile. Until the water flow out of the high radiation area is halted, we remain in the expansion of the problem mode, not the cleanup mode.

Can you describe that?

Letting the cores and their surroundings heat up is likely considered a recipe for hideous new problems. There is heat to be dealt with as well as escaping radioactive material, and clearly at the moment they worry more about the heat than the buildup of radioactive water. Its not fair to focus only on problems they are creating without acknowledging the problems their current actions are preventing.

I describe the cold shutdown they seek as being wrecked-reactor type because I cannot bring myself to describe what will hopefully happen to these reactors at some point as normal cold shutdown, that term is just too connected in my mind to the standard shutdowns that undamaged reactors go into routinely.

They are seeking to get proper cooling systems in place, which will keep the remains at stable temperatures below boiling point, and will enable them to reuse the water instead of ending up with ever more bad water to deal with. Thats the main thrust of the roadmap they aim to complete at some point, that will be declared a major milestone in dealing with the plant, etc etc. It clearly won't be the end of matters, but it will represent the end of the dramatic first chapters, and at that point we'll be better placed to argue what the medium and long term cleanups consist of.

There is always the chance they will be forced to change plans into something more crude & final, and perhaps more along the lines of what you would like to see happen. If for example they utterly fail to improve key working conditions inside reactor buildings, then they will have to think again.

And on that very topic, right now I wait nervously to see what their latest survey of reactor 2 building will reveal. Seeing as they have apparently succeeded in cooling its pool properly in recent days, they are hoping humidity levels have fallen, so that they may they try to deal with radioactive substances in the air in the building. Assuming that works, they can then carry out other work they have planned inside the building as per the roadmaps.

 

[jim hardy]

Unfortunately, after they discover that two water sensors and two pressure sensors in unit 1 were wrong we can't trust any data

i have faith in thermocouples so long as they're dry . Especially if they're wired right to the computer with no electronic doodads in between.

Pressures i have suspected ever since the explosions for when you drastically overrange a sense element you give it a "set" and it'll read high ever after.
Jorge's plots were real useful for trending but i expected pressures to be found reading high.
next couple days should tell about units 2 & 3.

Levels are subject to losing water in their sense lines, as when drywell gets real hot and instrument sense line heats up driving dissolved gas out of solution. So the gage reads in error by the height of any gas bubbles in its sense lines. They became unreliable IMHO as soon as depressurization began with no ventilation to drywell. Ever open a hot Coke?


that's why i spent so many hours staring at photographs looking for reactor parts..

Most computer electronics will start to act up after several thousand R which would be scores of Sv.
It'll be interesting to see how the Packbots hold up.

Time will tell.

 

[Jorge Stolfi]

i want to personally extend thanks to you for your work in making hose graphs. Curious, whatever happened to 3 on 21st accompanied high water injection through "fire line"? i don't know what fire line is - does it go into vessel(core spray perhaps) or does it spray down the drywell?

Thanks for the compliment. "Fire line" should have been "fire extinguisher line", the other plot being the flow through the "feedwater line". AFAIK, in an intact reactor both lines lead into the RPV; the former through a ring of spray nozzles near the top of the fuel, the second one through pipes on the turbine side, near the bottom of the fuel.

 

[SteveElbows]

Unfortunately, after they discover that two water sensors and two pressure sensors in unit 1 were wrong we can't trust any data

To be fair they always made it pretty clear that quite a lot of the data could be wrong. We know for a long time that some numbers must be totally wrong, where 2 indicators disagree with each other a lot, or where values go up and down in crazy ways or show - values.

Aside from slowly getting a few more bits of accurate data as they install new instruments, there isn't all that much more that I am expecting in terms of quality data that will give us a clear picture. Personally the most illuminating thing I can hope for in the weeks ahead is the english translation of TEPCOs long analysis document. The one that contains the estimates of core damage that we already know about in detail, but also estimates for containment damage, where we have only seen a few internet & press reports & a couple of paragraphs of the document that I machine translated. Although I can't speak Japanese I can tell by looking at it that it seems to contain some interesting graphs showing not just actual pressure & temperature data that we know already, but also what they think the temperatures & pressures really were at various times early on. Sometimes this differs considerably from the actual data, and there are handy events labelled on many of these graphs, such as the moments they think core, RPV and D/W or S/C damage happened.

 

[Astronuc]

Each of the situations at #s 1,2 and 3 are far worse than TMI.

Quite true. TMI-2 was operating in its first cycle with only ~62EFPD of production. The fission product inventory was quite low compared to the mature operation of the the Fukushima cores.

The way I see it, although the site around the containment structures can and should be cleaned up, the corium blobs themselves should not be disturbed.

There is nothing to be gained from mucking about with the corium.

There is no confirmation of corium. Only visual inspection can confirm corium.

It was thought that the fuel in SFP #4 had grossly failed, yet the visual evidence show little sign of melting or gross failure. Instead it appears that the spent fuel is largely intact. If so, it can be removed and placed in casks, which is the ideal situation.

The cooling of the fuel in the cores is necessary in order to mitigate/prevent further degradation of the cladding and the consequent release of fission products to the coolant.

Ideally, a closed loop cooling system would be established. Such as system would also include a processing system to collect any fission products, and the fission products would be solidified in order to preclude their transportation into the environment.

The fuel and core components will have to be removed eventually in order to decomission the reactor. Decomissioning has been accomplished at various sites in the US and Europe, so the process is well understood. The complication at Fukushima is the degradation of the cores, which could very well be comparable to TMI-2's core.

 

[hbjon]

I am sure we all remember the guy who went in and tried manhandle and wrestle around with a devil ray in his own elements. It is the unknow that overloads the analizer and becomes an unmanageable catastrophe. Since a lot of people have spent over 2 months agonizing over readings from faulty gauges and misinformation, why not take that advice and step back, take a deep breath, and find out where the sharp pointy sides of these devil rays are?

 

[jim hardy]

"""I am suggesting that the best thing to do right now is to stop pouring water into the nuclide pile. Until the water flow out of the high radiation area is halted, we remain in the expansion of the problem mode, not the cleanup mode.""

Many people don't appreciate what energy is.

To put it simply, think of the energy in that core as just another fluid. Early physicists called it "Caloric". The core is making it, that's the Decay Heat..

The "Caloric" will by hook or crook get out of that "Corium".
The "Corium" is most likely a crumbly debris bed that's still in the vessel.
If you bury the "Corium" the "Caloric" will i guarantee tunnel its way out and its radioactive friends will tag along.
They must continue to actively remove the decay heat.

Should the unthinkable happen the core will very quickly produce an unthinkably large amount of "Caloric" which will exit the area with pyrotechnics.

Water prevents fast unthinkable.
Boron prevents thermal unthinkable.
So it is important they continue applying borated water.

That they have done so is why the vessels are still able to make steam.
Wherever the steam is being made is where the cores are.

All they have to do is move heat and contain radiation.
Water is best stuff around for moving heat.
Their problem is containing the waterborne radiation.
If you know of a better substance than water please advise. Sand is no good for moving heat because it just doesn't pump worth a darn.

Kind of a Catch-22, ain't it?

 

[MadderDoc]

Thanks for the compliment. "Fire line" should have been "fire extinguisher line", the other plot being the flow through the "feedwater line". AFAIK, in an intact reactor both lines lead into the RPV; the former through a ring of spray nozzles near the top of the fuel, the second one through pipes on the turbine side, near the bottom of the fuel.

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

 

[Quim]

They must continue to actively remove the decay heat.

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

Should the unthinkable happen the core will very quickly produce an unthinkably large amount of "Caloric" which will exit the area with pyrotechnics.

Water prevents fast unthinkable.
Boron prevents thermal unthinkable.

Those days are over, without a moderator a (blob, hunk of, or puddle of) corium can't go critical with thermal reaction.

And a fast reaction is out of the question with 5% (or whatever) enrichment.

That they have done so is why the vessels are still able to make steam.

I see steam as being very undesirable, it is the pathway for nuclides to escape into the environment.

Water is best stuff around for moving heat.

But there is no need to "move" any heat. The heat is fine where it is.
Once the water is removed from the nuclide piles, heat becomes an academic subject. Containment is achieved.



I'm glad you're responding Jim, I know you won't get your feelings hurt as some here would if they attempted to hold up your side of this discussion.

 

[sp2]

Not necessarily so. One has no evidence of 'blobs of corium'. Any reference to corium is speculation.

Those outside of industry have little credibility regarding the state of the reactor/core/fuel.

There is an appropriate engineering solution, but it is unlikely to come from outside the industry.

'SOLUTION?' "There is an appropriate engineering SOLUTION?"

With all due respect, Astronuc, you need to use a different word.
There may be a best 'response.' There may be wiser 'options.'

But a 'SOLUTION?'

Is there a 'solution' that'll magically erase the millions of terabecquerels already released?
That'll decontaminate every fish, and every piece of seaweed in 10,000 square miles of ocean?
That'll somehow neatly suck up the layer of Cs-137 over hundreds of square km of countryside, that's already heavier than that of the Exclusion Zone in Chernobyl?
That'll perfectly clean up the contaminated spinach and tea 200 miles from the site?

I'm sorry, but talk of a 'solution' to Fukushima is the kind of Orwellian language that makes reasonable people around the world so profoundly distrust the nuclear industry.

 

[Quim]

makes reasonable people around the world so profoundly distrust the nuclear industry.

That highlights a statement I made in post #8854.
"But the other side is just as bad"


Why not just let the cards fall where they may?

 

[biffvernon]

But there is no need to "move" any heat. The heat is fine where it is.
Once the water is removed from the nuclide piles, heat becomes an academic subject. Containment is achieved.

Er...I don't think heat can be contained. You might slow down it's transfer for a while but that just stores up a bigger problem for later.

 

[Quim]

Er...I don't think heat can be contained. You might slow down it's transfer for a while but that just stores up a bigger problem for later.

Where I said: " Containment is achieved" I was referring to containment of radioactive material.

Heat in itself is not a problem IMO.

I assume that the end result will be a 5 - 10 acre parcel of land which has no source of ground water and is quite hot on its upper surface and warm tapering to ambient on its perimeter.

This would be a very low maintenance site.
Also, this would be leakproof as far as radiation is concerned.


If you are trying to say that this "solution" wouldn't have an acceptable political end result, you should probably post that in the more political forum.

 

[Jorge Stolfi]

Why not let [corium] reach its own equilibrium?
Hot sand, gravel, concrete or dirt is no threat to anything or anyone.
But there is no need to "move" any heat. The heat is fine where it is.
Once the water is removed from the nuclide piles, heat becomes an academic subject.

The problem is that you don't have a fixed amount of heat (as in ordinary molten iron), but rather megawatts of heat being produced continuously. If you enclose wht remains of the fuel (in whatever form or mixture) within a poorly conducting material, the mass will keep getting hotter until the uranium oxide itself boils.

 

[biffvernon]

Indeed. It's a question of whether the heat conduction through the sand or whatever is fast enough to stop the corium boiling. If yes, that's fine. If no, then that very much not fine at all.

 

[hbjon]

Er...I don't think heat can be contained. You might slow down it's transfer for a while but that just stores up a bigger problem for later.

The quantity of fuel is an important factor to consider. Jim aint a whistling dixie when he says there is a lot of potential energy at this site. I remember reading about the Mass Defect and the conversion of matter to energy in high school. If you bury everything in sand, I believe the fuel will realize it's full potential in time. I side with Jim on this. But I am just one of the backseat drivers around here.

 

[Astronuc]

'SOLUTION?' "There is an appropriate engineering SOLUTION?"

With all due respect, Astronuc, you need to use a different word.
There may be a best 'response.' There may be wiser 'options.'

But a 'SOLUTION?'

Is there a 'solution' that'll magically erase the millions of terabecquerels already released?
That'll decontaminate every fish, and every piece of seaweed in 10,000 square miles of ocean?
That'll somehow neatly suck up the layer of Cs-137 over hundreds of square km of countryside, that's already heavier than that of the Exclusion Zone in Chernobyl?
That'll perfectly clean up the contaminated spinach and tea 200 miles from the site?

I'm sorry, but talk of a 'solution' to Fukushima is the kind of Orwellian language that makhes reasonable people around the world so profoundly distrust the nuclear industry.

I was referring only to the current state of the damaged cores and SFPs at Fukushima units 1-4. I do not include the contamination due to the release of fission products so far; this is an entirely different problem, although one rooted in the same precursor.

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

My immediate concern is the situation at hand, and the minimization of further contamination - aside from the technical considerations.

The imperative is to cool the cores in order to reduce/mitigate further release of fission products. Then, to the extent possible, a closed system for cooling and prodessing of the radwaste must be established. To the extent possible, a containment system must be established to prevent further releases into to the atmosphere. These are the technical considerations.

 

[Quim]

The problem is that you don't have a fixed amount of heat (as in ordinary molten iron), but rather megawatts of heat being produced continuously. If you enclose wht remains of the fuel (in whatever form or mixture) within a poorly conducting material, the mass will keep getting hotter until the uranium oxide itself boils.

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.

 

[Quim]

Indeed. It's a question of whether the heat conduction through the sand or whatever is fast enough to stop the corium boiling. If yes, that's fine. If no, then that very much not fine at all.

Agreed!

 

[SteveElbows]

Well as expected we now learn how the humidity has changed in reactor 2 since the successful pool cooling.

Not terribly surprisingly the news is bad, it has not changed. It was probably always wishful thinking that the pool was responsible for most of the humidity inside reactor 2 building, but they had to rule it out.

One alternative plan of action they are talking about seems to involve opening the door!

http://www3.nhk.or.jp/daily/english/06_02.html

 

[jim hardy]

""But I am just one of the backseat drivers around here.""

thanks hbjon i too am out of my league here. i do remember my high school physics though.

So did Frank Sinatra - to paraphrase:

"When an unstoppable force like (decay heat) meets an immovable object like (perfectly insulating mountain of sand), something's got to give".

not trying to start a war of words here, just we got to keep our thinkin' straight.

i appreciate when people point out my slips.

And i am not talking down to anyone. i try always to put things in simple language because it keeps my thinking straight.
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.

old jim

 

[Borek]

But there is no need to "move" any heat. The heat is fine where it is.
Once the water is removed from the nuclide piles, heat becomes an academic subject. Containment is achieved.

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.

 

[Bioengineer01]

There is the saying: never say never. Certainly this recent tragedy is once again a testament to this philosophy and a stark reminder to all engineers and scientists.

Given that disclaimer, these civilian nuclear reactors are designed with contingency in place to ensure they (for the most parts) do not go critical when they aggregate into a lumped mass corium at the bottom of a reactor containment and beyond. This is because firstly the nuclear fuel is of low purity in terms of fissile elements. Secondly, neutrons generated directly from fission of say uranium have too high energy - this results in a low probability of causing other fission events of other uranium atoms thereby eventually freezing out a chain reaction.

These reactors are purposely designed to have neutron moderators placed between fuel rods to slow down and reduce the energy of these neutrons from fission, so that they can cause fission and sustain a chain reaction. In other words, when fuel rods are melted down into a corium, there is presumably no more neutron moderators between the fuel rods and fuel elements (that is, the water), thereby from that point on you are primarily concerned with high energy neutrons generated from fission which have low probability of sustaining a chain reaction while thermal neutrons (lower energy) that can sustain a chain reaction are reduced in a hypothetical corium configuration.

This is the best case scenario of course. If it so happens that the civil structure of the plant itself unknowingly had neutron reflecting material nearby, it may be able to sustain a reaction to a degree. Theres also the possibility that the corium achieves localized critical mass configurations within the corium that can sustain a reaction (though not likely as the fuel is purposly designed to have low purity and is assumed to be homogenous in composition). All of this is purely hypothetical of course as are any other plausible scenarios people can draw up.

That is also not the end of the story of course, as life is never that perfect: it is not just 100% fuel configuration with control rods in place or 100% corium lump mass. If it is partially melted with a corium and some spent fuel assembies, presumably with neutron moderating water inbetween, this can again lead to criticality, especially since control rods that would have otherwise prevented criticality may be ineffective to block neutrons between the corium and the fuel assemblies though they will be far away in distance and the reaction rate should not be very high.

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...