Energy From Thorium Discussion Forum

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PostPosted: Mar 11, 2010 2:10 pm 
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Just throwing this one out there: I've been wondering if there is any method by which fluoride salts could be separated by mass as a possible alternative to fractional distillation.

If we're talking about cleaning out the fission byproducts from a fuel salt mixture then there's obviously going to be a difference in mass. Most fission byproducts have a mass in the range of between 90 and 100 AMU's or 130 to 140 AMU's. This is signifficantly less than uranium or thorium. In the proposed thorium fueled reactors, uranium-233 would be the primary fuel and small amounts of U-234 and U-235 would also be left in the reactor to fission.

Lithium and Beryllium, the carrier salts are much lighter than either of these.

I had a couple of thoughts for possible mechanisms: a liquid centrifuge seperater of sorts, where the uranium salts would collect at the bottom and fission byproducts would tend to accumulate above uranium salts. The other possibility: Some type of membrane system where the salts would be dissolved in a solvent and forced through membranes with varying size openings - something like reverse osmosis.


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PostPosted: Mar 11, 2010 3:53 pm 
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On the light side you would want to separate BeF2 (47 = 9+2*19) from RbF (104=85+19)
On the heavy side it would be EuF3 (210 = 153+3*19) from UF3 (290 = 233+3*19)

If such a scheme works one advantage would be that it also picks up the real heavies like Am, Cm, etc.
But I don't know how good a separation one could hope for with such a scheme.
The concentrations of fission products are pretty low.
The fission products by themselves are like not a liquid but rather a solid even at 1200C.


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PostPosted: Mar 11, 2010 3:58 pm 
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Joined: Mar 07, 2007 11:02 am
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Location: Ottawa
A friend gave me the conference proceedings for

AIP conference proceedings- Internation conference on accelerator driven transmutation technologies and application. Las Vegas Nevada July 25-29 1994.

Specifically to show me a paper on centrifuge separation of molten salts. There may have even been more than one (it is massive 1000 page document and 75Meg). I converted the one centrifuge paper I found. Interesting but I found it a bit too exotic for my tastes (i.e. sounds like a great deal of R&D with no promise of success).

Attachment:
Centrifuge94onepaper.pdf [1.97 MiB]
Downloaded 244 times


David L.


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PostPosted: Mar 11, 2010 5:17 pm 
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Still, this is something that looks like a worthy avenue to try for Pu, Am, and Cm separation from fission products.
No hurry though. We don't need this for a few decades after the first LFTR is turned on.


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PostPosted: Mar 12, 2010 12:18 am 
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Joined: Nov 18, 2007 11:52 pm
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Lars wrote:
On the light side you would want to separate BeF2 (47 = 9+2*19) from RbF (104=85+19)
On the heavy side it would be EuF3 (210 = 153+3*19) from UF3 (290 = 233+3*19)

If such a scheme works one advantage would be that it also picks up the real heavies like Am, Cm, etc.


I agree, although assuming a thorium cycle, those kind of transurics are going to be very very rare. Anything up to Pu-239 can be just considered to be a fuel and left in to fission. Only when you get up past Pu-240 and into Americium and so on do you really have anything that's worth separating, and it will take many decades for that to accumulate to any degree that's even worth worrying about.

Although I can see other reasons for removing plutonium-238, which is the isotope that would first accumulate. Also Am-241, Cm-252 and so on.

I find the very notion that something like pu-238 is something that efforts should be made to avoid creating or that should be destroyed or disposed of. I can't think of too many other materials that people worry about "disposing of" despite being worth signifficantly more than its weight in gold.

Every time I hear someone complain about something like Californium or Plutonium-238 or even Americium-241, I think of someone complaining "Oh no! This reactor keeps spitting out gold bars and hundred dollar bills! How can we stop it from making this extremely valuable material!"


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