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 Post subject: Re: PRISM
PostPosted: Nov 02, 2010 12:57 pm 
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Tim Flavin wrote:
Is there any reason not to use molten salt like LiF or BeF2 instead of sodium for cooling a PRISM type reactor? It gets rig of the liquid sodium and might act as a moderator.

PRISM is a fairly hard spectrum fast neutron reactor -- even its fuel is metal (which is a big part of the reason why the spectrum is "hard" - i.e. biased towards the high end of fission neutron energies, which go roughly to about 2 to 4 MeV).

Substituting the sodium metal coolant with lighter elements, would significantly soften the spectrum, thereby degrading some of the design objectives.

LiF or BeF2 would definitely do that -- mostly due to the Li and Be, not so much the fluorine (F is mass 19, vs. 24 for Na).
Chlorides would be better than fluorides, preferably paired with Na or Rb.


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 Post subject: Re: PRISM
PostPosted: Nov 02, 2010 4:11 pm 
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Tim Flavin wrote:
Is there any reason not to use molten salt like LiF or BeF2 instead of sodium for cooling a PRISM type reactor? It gets rig of the liquid sodium and might act as a moderator.


I would assume because you will no longer have a fast spectrum reactor with a moderating coolant.


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 Post subject: Re: PRISM
PostPosted: Nov 03, 2010 12:27 pm 
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cld12pk2go wrote:
I would assume because you will no longer have a fast spectrum reactor with a moderating coolant.

It also depends on the density.
For example, it is possible to have a fast reactor that is gas- or vapour-cooled with light atoms like helium gas or steam -- which would be very effective moderators in the condensed state.


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 Post subject: Re: PRISM
PostPosted: Nov 03, 2010 3:09 pm 
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OK are there any salts that don't act as moderators too much? NaCl possibly?


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 Post subject: Re: PRISM
PostPosted: Nov 03, 2010 4:35 pm 
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Tim Flavin wrote:
OK are there any salts that don't act as moderators too much? NaCl possibly?


NaCl, KCl, MgCl2.

NaCl-MgCl2 eutectic probably has the best of traits for a fuel salt. For further reading, there are excellent documents in the chloride reactor portion of the document repository.

http://www.energyfromthorium.com/LCFRbiblio.html


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 Post subject: Re: PRISM
PostPosted: Nov 04, 2010 10:04 am 
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Quote:
For further reading, there are excellent documents in the chloride reactor portion of the document repository.

Thanks, I hadn't found that page yet.


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 Post subject: Re: PRISM
PostPosted: Nov 04, 2010 12:16 pm 
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By the way I found a lot if useful molten salt phase diagrams here. Including NaCl-MgCl2.


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