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Tags Fukushima , nuclear accident

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Old 7th December 2011, 08:06 AM   #1
metamars
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Can Tin Ball Bearings Save the Fukushima nuclear reactors from the China Syndrome?

I have a simple idea that I would like to hear feedback on. Let me admit, right off, that I haven't studied the nuclear reactor geometry in any detail, and this idea depends on such geometric (or layout) conditions.

As some of you may know, Fukushima is threatening (or has already begun), to go China Syndrome.

The simple idea is this: Build a wall around the Fukushima reactors, and start dumping in tin ball bearings. Very tiny ones, so that they are more space-filling, and can pour through smaller openings. If you need to, drill some holes through floors, tops of containments, etc.

If the nuclear materials are hot enough to melt concrete, then they are hot enough to melt the ball bearing. Concrete becomes "crumbly" at around 1000 C, and it's constituent stone and sand don't melt until 2600 C, according to this. The melting point of tin is 231.9 C.

Meanwhile, the thermal conductivity of tin is 67 W/(m.K), vs. .1- 1.8 W/(m.K) for concrete. (Ref).

Consequently, provided that you can get the tin ball bearings close enough to the bottom of the reactor where the nuclear materials are eating through the concrete, they should both melt faster than the concrete, and furthermore conduct the vast majority of heat upwards, throught the mass of tin, rather than downwards.

Should the tin that's enclosed become completely melted, you build a second wall, knock a hole in your first wall, to let the liquid tin pour through, and dump fresh tin ball bearings on the top of the reactor, within the circumference of the first wall. Repeat, as necessary. (I.e., as many additional walls as you need.

If you want to conserve energy, and the tin is not too radioactive, you can create a tin can factory, right there! :-) (I don't think tin cans have tin, anymore. Just kidding, in this last paragraph.)

Last edited by metamars; 7th December 2011 at 08:16 AM.
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Old 7th December 2011, 09:05 AM   #2
ellindsey
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Fukushima isn't threatening to go 'China Syndrome', even if such a thing were possible. The cores of the three damaged units have been under water and below melting temperature for quite some time now. Whatever melting occurred happened in the first few days after the earthquake.
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Old 7th December 2011, 09:13 AM   #3
metamars
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Originally Posted by ellindsey View Post
Fukushima isn't threatening to go 'China Syndrome', even if such a thing were possible. The cores of the three damaged units have been under water and below melting temperature for quite some time now. Whatever melting occurred happened in the first few days after the earthquake.
Below melting temperature of what? Also, my reference is dated Nov. 30. What is the date (and source) of your information?
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Old 7th December 2011, 09:17 AM   #4
ellindsey
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My reference here:

http://www.tepco.co.jp/en/nu/fukushi...11130_04-e.pdf

This is dated November 30th. Note that as shown on page 15, temperatures inside unit 1 are below 100 degrees Celsius and have been for quite some time. Units 2 and 3 less badly damaged than units 1.

Claims that the cores are still molten and eating their way through the earth are contrary to available evidence and belong in the Conspiracy Theories section. For one thing, you'd have to explain a way for the material to be somehow still molten yet not transferring any of that heat to the water that's covering them.
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Old 7th December 2011, 09:21 AM   #5
Mikemcc
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All of the affected cores are in 'cold shutdown' now. The temperatures are less than that of boiling water.
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Old 7th December 2011, 12:46 PM   #6
metamars
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Originally Posted by ellindsey View Post
My reference here:

http://www.tepco.co.jp/en/nu/fukushi...11130_04-e.pdf

This is dated November 30th. Note that as shown on page 15, temperatures inside unit 1 are below 100 degrees Celsius and have been for quite some time. Units 2 and 3 less badly damaged than units 1.

Claims that the cores are still molten and eating their way through the earth are contrary to available evidence and belong in the Conspiracy Theories section. For one thing, you'd have to explain a way for the material to be somehow still molten yet not transferring any of that heat to the water that's covering them.
OK, thanks. My reference's source is the architect of "Reactor No. 3 and former president of Saga University". However, I don't see where he addresses the sustained low temperatures. Maybe he thinks they're just fabricated?
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Old 7th December 2011, 01:07 PM   #7
geni
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Originally Posted by ellindsey View Post

[/quote]

Tepco aren't exactly a reliable source.
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Old 7th December 2011, 01:14 PM   #8
ellindsey
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I don't know of any more reliable source for what's going on at Fukushima.

If you are claiming that Tepco is fabricating the temperature plots and other evidence, then this thread should be moved to Conspiracy Theories. For the cores to still be molten and actively eroding their way through the containment would require a lot of evidence to be faked and a lot of people to be in on the cover-up.
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Old 7th December 2011, 01:22 PM   #9
Wolrab
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I would be more like South Atlantic Syndrome:
http://www.antipodr.com/?addr=fukishima+japan&x=0&y=0
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Old 7th December 2011, 01:29 PM   #10
not_so_new
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Okay so this thread has already split.....

1. Are the reactors still hot and threatening to go through the floor?

2. Would the OP'ers idea work if we assume that the reactors are melting down?

I think The answer is probably NO to #1. At least not from everything I have heard but I would like to hear more on the subject.

I don't know the answer to #2 but forgetting about #1 above for sake of argument. Take it as a hypothetical situation, would tin ball bearings actually (theoretically) help?
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Old 7th December 2011, 01:39 PM   #11
ellindsey
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I think the danger with actually trying what the OP is suggesting is that the tin ball bearings could actually become hot enough to ignite, or at least oxidize, and in doing so add more energy to what you're trying to cool off. I'm not completely sure of the flammability of solid tin under those conditions however.
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Old 7th December 2011, 01:59 PM   #12
geni
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Originally Posted by not_so_new View Post
Okay so this thread has already split.....

1. Are the reactors still hot and threatening to go through the floor?
Probably not.

Quote:
2. Would the OP'ers idea work if we assume that the reactors are melting down?
Your problem is defining work. Liquid metal cooling (personaly I'd be tempted to use gallium) should have some impact but you would probably expect the fuel to melt through the tin and come into dirrect contact with the concrete. The question would be I suppose would you be better off just using water and dealing with the effects of the steam explosions.
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Old 7th December 2011, 02:00 PM   #13
geni
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Originally Posted by ellindsey View Post
I don't know of any more reliable source for what's going on at Fukushima.
Yes which is why I'm rather glad I live a long way away from it.
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Old 7th December 2011, 03:58 PM   #14
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When the tin at the bottom reaches its boiling point (2600 C) then it will be a matter of fluid dynamics and the shape of the vessel in determining whether small bubbles rise to the top or the expanding gases shoot molten tin into the sky. A dangerous but, I suspect, awesome sight.
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Old 7th December 2011, 04:01 PM   #15
ben m
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With regards to the question "is the reactor still fissioning", you don't have to trust TEPCO. Everyone and their brother (the IAEA, the DOE, the EPA, U. Washington, etc.) is monitoring the radionuclides emitted; I've seen the raw data on this and it is precisely consistent with the TEPCO claims. The reactor went into "hot shutdown" when the earthquake hit, went into loss-of-coolant meltdown after the tsunami hit, and released radiation from hot, but not actively fissioning, damaged fuel when the hydrogen explosion breached the 2nd containment. (I'm still not clear on exactly when the pressure vessel was breached---by the earthquake, by a pressure spike after loss-of-coolant, or by hydrogen explosions?)

There is no question whatsoever about this; if it were still fissioning, the released radiation would be totally different (Kr, Xe, and I rather than Cs and Sr.)

More generally, I don't think that a China-syndrome-like scenario is possible for a low-enriched fuel like that in a modern water-moderated reactor. The fact is that, unless neutrons are quickly brought down to low energies, U238 itself (80-90% of the fuel) serves as a control rod---it has a high absorption cross section and it sops up epithermal neutrons. The only way to get a chain reaction is to have the fuel and the "moderator" (neutron energy degrader) intimately mixed together, as in an intact-ish fuel bundle. If you melt all the fuel into a blob, there's not enough moderator, and you lose neutrons---virtually all of them---to 238U(n,gamma) reactions. If you spread the fuel out in a larger puddle of some sort, there's too much moderator, and you lose neutrons to H(n,gamma) reactions. (And too much free surface, you lose neutrons to the outside.)

A complete-core-meltdown-and-pressure-vessel-breach would indeed be a very bad thing, but it would be a very bad hot spent fuel spill---it would not be a "critical reactor melting its way downwards".
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Old 7th December 2011, 05:09 PM   #16
ben m
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Let's suppose that you *did* have a melting reactor---say, a puddle of highly enriched uranium-carbide, with Doppler broadening stabilizing the reactivity. And let's look at your tin scenario in that case.

You're mistaken, I think, to picture heat getting conducted through a block (or a puddle) of solid or molten tin. Look at that conductivity number---67 W/(m.K). Let's suppose there are 100m^2 of tin in contact with the hot core, and you've piled it up to 1 meter thick. That will conduct out 6700 watts per K. Um! But a working reactor is ~1 GW; even a recently-shut-down-reactor is 50 MW. That won't reach thermal equilibrium until the interior is 7000K hotter than the exterior---which means it's boiled, which means it's cracked itself open and exploded.

You want to get the heat out much faster than conduction---even very good conduction---is capable of, in such a compact geometry. (Nuclear fuel assemblies are carefully engineered just to get heat to conduct the 1mm from the center of a fuel pellet to the surface.) You need convection advection, which means you need a flowing coolant.

Last edited by ben m; 7th December 2011 at 06:19 PM. Reason: convection/advection
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Old 7th December 2011, 06:08 PM   #17
Checkmite
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Tin is lighter than uranium. Once the tin melts, it will never have a chance to get between the molten uranium and the floor of the reactor, because it will immediately rise to the top of the molten uranium.
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Old 8th December 2011, 02:45 PM   #18
geni
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Originally Posted by ben m View Post
You need convection advection, which means you need a flowing coolant.
Yes but liquid metal is a perfectly valid solution to that.
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Old 9th December 2011, 07:34 AM   #19
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Originally Posted by geni View Post
Yes but liquid metal is a perfectly valid solution to that.
I think in this sense, flowing is intended in a more predictable and probably controlled manner. The tin would melt around the heat source, but it would not be carried away in a manner to prevent bad things from happening.
Originally Posted by ben m
That won't reach thermal equilibrium until the interior is 7000K hotter than the exterior---which means it's boiled, which means it's cracked itself open and exploded.
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