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PostPosted: Feb 02, 2010 10:27 am 
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For a single fluid salt system (and maybe even Two Fluid) it is likely Liquid Bismuth Reductive Extraction (LBRE) is still the leading candidate for fission product removal. Anyone come across any comments about its viability for use with ZrF4 containing salts (i.e. NaF-ZrF4)? I ask because I know that when used with flibe salts that Zr goes along with the transuranics and Pa (at least for the DMSR reprocessing scheme). This would imply that Zr in the carrier salt would cause a problem if you are trying to remove and recycle transuranics. There was much work on NaF-ZrF4 as a carrier salt for burning spent fuel transuranics and I believe they expected to use LBRE to remove the fission products. Perhaps you just have to fine tune the process to get around ZrF4? Anyone have some more concrete thoughts?

David LeBlanc

P.S. I mention this for Two Fluid as well because while vacuum distillation might sound better we don`t know yet if it is the best. LBRE is a much simpler process without thorium and ORNL often mentioned how you only have to handle liquids, not solids like you do with vacuum distillation (although I`m not sure what they meant about solids and vacuum distillation, perhaps the still bottoms you need to clean out?). Also vacuum distillation doesn`t help you with the transuranics beyond Np (even a pure Th-U233 cycle would probably produce at least 10 or 20kg per GWe year and ruin the claim of being 10,000 times less long lived waste than an LWR).


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PostPosted: Feb 02, 2010 10:57 am 
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Zr is a fission product.


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PostPosted: Feb 02, 2010 11:57 am 
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David,
Regarding vacuum distilling. "and ruin the claim ..."

Just because we do not remove the plutonium and recycle it on-site does not mean we never do it. It makes some sense to do this at a central repository. The flows here are quite modest and there is a political disadvantage to deploying on-site plutonium isolation technology. Even though our plutonium is useless for weapons (due to the fact that it is >50% Pu238) there is concern about spreading such knowledge. So while there may be some modest performance penalty for doing the plutonium extraction at a central location rather than on-site I'm thinking we are better off accepting the performance penalty (of delayed processing of the plutonium) in trade for fewer arguments about proliferation.

We still reduce the plutonium production by 90+% and eventually the residual plutonium by >10,000x.


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PostPosted: Feb 02, 2010 12:59 pm 
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jaro wrote:
Zr is a fission product.


???

Yes and as a fission product it still ends up as ZrF4. My question was simply if carrier salts that purposefully have lots of ZrF4 unduly complicate liquid bismuth reductive extraction (or some of the more modern but related methods). You don`t want to strip out all the ZrF4 from the carrier salt and then have to recombine it later.

David L.


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PostPosted: Feb 02, 2010 1:05 pm 
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Lars wrote:
David,
Regarding vacuum distilling. "and ruin the claim ..."

Just because we do not remove the plutonium and recycle it on-site does not mean we never do it. It makes some sense to do this at a central repository. The flows here are quite modest and there is a political disadvantage to deploying on-site plutonium isolation technology. Even though our plutonium is useless for weapons (due to the fact that it is >50% Pu238) there is concern about spreading such knowledge. So while there may be some modest performance penalty for doing the plutonium extraction at a central location rather than on-site I'm thinking we are better off accepting the performance penalty (of delayed processing of the plutonium) in trade for fewer arguments about proliferation.

We still reduce the plutonium production by 90+% and eventually the residual plutonium by >10,000x.



Yes point taken. I was just pointing out that if you try to directly compare vacuum distillation to LBRE for Two Fluid work that you need to remember that you`ve got some fairly nasty transuranics in the still bottoms that you need to worry about.

So anybody know how ZrF4 as part of the carrier salt effects LBRE or any of the more modern techniques since it seems to associate with the higher transuranics?

David L.


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PostPosted: Feb 03, 2010 3:10 am 
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From ORNL5176 Feb 1977
The most recent ORNL report on the metal transfer process I've found.

page 45.
The overall mass-transfer coefficients for rare earths across the
salt and bismuth phases determined in experiments MTE-3 and MTE-3B were
only about 1 t o 50% of those that would be predicted by currently
available correlations, with the largest discrepancy occurring at the
lithium chloride--bismuth interfaces.



page 49.
have been determined to be in the range of l0^4 to l0^8 for the trivalent and
divalent rare earths. Thus negligible loss of thorium from the fuel salt occurs in the process.

As of that date the separation was very good (although I don't see how the flows work out) so little thorium was wasted but the flow rate was very low. They were trying for 1% of the full rate (for a 100 day processing rate) for a 1 GWe plant and achieved only 1-50% of their goal. It appears that as of that time there was still some basic science to solve.


Do you read this report differently? Or what is the basis for thinking that this approach will work well?


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PostPosted: Feb 03, 2010 9:27 am 
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Lars,

I`ve gone through that LBRE document, it is a very tough read. They talk about how their "correlations" from previous experiments using agitators didn`t give a good prediction but I am not sure how well it actually worked overall since the conclusions don`t sound all that negative. I am certainly not saying I favor LBRE over vacuum distillation but the fact is that just about every serious effort for the last 30 years has assumed its use from the DMSR break even version of the late 70s to the more recent French and Russian efforts. The process is enormously simplified for a Two Fluid design where you are not trying to work around thorium (or for a 1 and 1/2 Fluid design where you allow some thorium loss). I don`t think anyone has enough information yet to choose LBRE versus vacuum distillation for a Two Fluid (I used to just assume vacuum distillation was simplest but not so sure anymore).

For treating the still bottoms of a vacuum still or the end of life salt of a 30 Year Single Fluid DMSR we still probably need some method for pulling out transuranics (especially Am and Cm since there is no way to fluorinate those like you can maybe do for Pu). So again I am just curious to whether ZrF4 in the carrier salt makes LBRE really difficult or not.

David L.


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PostPosted: Feb 03, 2010 11:45 am 
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A quick google search turns up that ZrF4 is very volatile so it will likely come out in vacuum distilling - I think even before the lithium and beryllium do.

rm1.cc.lehigh.edu:8080/dept/IMI/OPGpdf/Lecture19.pdf

"A particular aspect concerning ZrF4 is that, at 1 atm of pressure, rather than melting like most glass-forming compounds, it sublimates at ~ 900 oC, exhibiting an appreciable vapor pressure at temperatures above 600 oC."

Indeed, I wonder when the Zr comes out in the distilling plan Luke came up with. In separate steps we did (U), (Cs), (Li, Be), (Th), the rest stays liquid. I'm hoping the Zr looks like Cs and comes out mostly in that step.

If we can operate around 1200C then I think we stay liquid the whole time but I do not know what happens to the solubility of fission product fluorides when we have removed the Li, and Be so that the solution is really molten ThF4.

I think I have a physical layout for the vacuum distilling that allows continuous distilling assuming there are no precipitates. Using the rates from the ORNL report it isn't very large and doesn't take much power.


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PostPosted: Feb 03, 2010 6:23 pm 
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We discussed what to do with the Zr towards the end of the high temp still thread Lars mentioned a ZrF4 vapour pressure of 17.6 Torr @1200C, about twice that of LiF. This matches the ORNL data of ZrF4/LiF volatility ratio being about 2, but not with the literature boiling point of 905C. There may be ZrF4-LiF complexes, which lower the ZrF4 volatility greatly.

Continuous operation would be great, but needs several stills at different pressures chained together. At too low a pressure, UF4 will sublime, not distil, and the solid could block things up. ZrF4 always sublimes.


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PostPosted: Feb 03, 2010 7:11 pm 
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Yes, I know that ZrF4 is no problem with a vacuum still, my question was if anyone knows if it causes a problem with Liquid Bismuth Reductive Extraction or one of the other electrochemical techniques if we want ZrF4 in a carrier salt. Again I ask because Zr was supposed to travel with the transuranics in LBRE but some fairly recent papers associate LBRE with the carrier salt NaF-ZrF4 for transuranic burner designs.

David


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