Energy From Thorium Discussion Forum

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PostPosted: Dec 29, 2012 7:05 am 
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One of the earliest methods of isotopic separation was mass spectrometry. It's proven and produces almost total separation in just one step. It also has very low throughput and massive energy requirements.

I wonder if it may be possible to use it for LFTR processing. In a two-fluid reactor, after fluorinating the uranium out and boiling the carrier salt the still bottoms are a relatively small volume so it might be feasible to process it by mass spectrometry at reasonable cost. This can be used to achieve virtually zero leakage of TRUs in the fission product stream and perfect separation of useful valuable fission products.

Is this idea totally crazy or not?


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PostPosted: Dec 29, 2012 8:43 am 
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My question is why would we want to? Most of the stuff we would want to separate should be chemically separable. Where would we need to get to the isotope stage?

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PostPosted: Dec 29, 2012 11:35 am 
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Keep repeating: Cheaper than coal. Isotropic separation should be kept just for building the reactor not fueling it or processing the waste - until we have exhausted other choices. For processing the wastes the first choice should be separation by physical properties, then chemical separation in a process that nearly completely recycles its reagents.

Based on ORNL's results from the falling drops experiment we can get to less than 100 grams of plutonium per GWe. I think this means we still have to vitrify the unused fission products and bury them deep but the plutonium poses no heat load challenges to geological disposal and the amount is so low that even if someone dug it up millenia from now the exposure to the world is modest.

We could try to drive it even lower. I don't think isotropic separation would be appropriate but perhaps some other techniques (like the electro separation used in EBR2, or liquid metal exchange proposed for MSBR) could clean things up just a little bit more. If we wish to remove the Am,Cm we will have to try something like that anyway since it is not expected that these will come out with fluorination.

The 250-300kg of plutonium produced each year in an LWR can be burned off in a thermal reactor (2/3rd fission of 239Pu, 80% fission of 241Pu) so that we end up with 30-40 kg (too lazy this morning to do a careful calc) of Am per GWe-yr of LWR operation.

The 20kg of 238Pu generated in a thorium fed LFTR will result in 1.5kg of Am assuming we burn off the plutonium in a thermal reactor.

So you can see that after fluorination (note not so simple due to handling challenges of 650C F2 but seems solvable to me) and burning off plutonium isn't the main TRU we have left to deal with.


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PostPosted: Dec 30, 2012 1:59 am 
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Joined: Apr 19, 2008 1:06 am
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Why should processing always be thought of in terms of waste disposal? Unfortunately, the pure Pu239 product has a weapons stigma. Otherwise it could be enrichment of certain fissile isotopes.
99.995% 7Li required in FLiBe, the life blood of a thermal LFTR, can be bast obtained by mass spectrometery as 6Li is a neutron poison. For the die-hard thermal LFTR fans, I prescribe a FNaBe based LFTreactor (CR<1) to power mass spectrometery for separation of 7Li.


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