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PostPosted: Apr 23, 2016 4:33 pm 
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A reply to a posting in the General Discussion brings to mind a couple of questions regarding "unspent" MSR fuel:

When a MSR (burner or breeder) is decommissioned, or is at the end of its design life, how much time is available before the remaining uranium needs to be removed before UF6 is formed. I've read the unspent fuel from the MSRE caused a problem in later years. Do any of the fission products or transuranics such as pu 239 have the same issue or can they be left in the fuel salt until reprocessing is performed, or, the unspent fuel is put is storage?


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PostPosted: Apr 24, 2016 5:47 am 
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UF6 can only be formed in an oxidising atmosphere. With so much of metal around, it is a reducing mixture You could extract uranium as UF6 by oxidising the fuel with fluorine or other fluoridating agent.


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PostPosted: Apr 25, 2016 12:05 am 
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jagdish wrote:
UF6 can only be formed in an oxidising atmosphere. With so much of metal around, it is a reducing mixture You could extract uranium as UF6 by oxidising the fuel with fluorine or other fluoridating agent.
For that it needs to be molten. After solidifaction, as the fission products decay, some release F+ ions that will attach to the nearest receiver. That is frequently whatever UF4 or UF5 that is near by. That is wht happened to the MSRE when they shut it down.

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PostPosted: Apr 25, 2016 2:18 pm 
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What about dispersing the fuel into a barium hydroxide slurry?
Any hexafluoride that forms will immediately hydrolyse and the hydrofluoride acid will be neutralised by the barium hydroxide.
After the neutralisation has occured you can calcine the slurry for long term storage.


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PostPosted: Apr 25, 2016 11:32 pm 
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Any additional non-volatile materials will only add to waste. The solution is partition by chloride/fluoride volatility and fractional crystallisation. Recombine and recycle.
Highly radioactive products can be used as decay energy sources as in RTG. Neutron poisons are mostly rare earths and could be ferromagnetic materials. Actinides are nuclear fuel.


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PostPosted: Apr 26, 2016 1:57 am 
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E Ireland wrote:
What about dispersing the fuel into a barium hydroxide slurry?
Any hexafluoride that forms will immediately hydrolyse and the hydrofluoride acid will be neutralised by the barium hydroxide.
After the neutralisation has occured you can calcine the slurry for long term storage.
Just remove the U via fluoride volatility.

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PostPosted: Apr 26, 2016 10:46 am 
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Assuming you have a fluoride volatility plant that actually works.
If we do, then you can just convert the remaining salt directly into a glass waste form using this process.


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PostPosted: Apr 28, 2016 4:17 am 
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Removal of uranium and zirconium cladding as volatile salts will reduce the waste to a quantity manageable by deep borehole disposal.


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