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PostPosted: Dec 23, 2010 5:44 pm 
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Folks, some of you have chemical engineering backgrounds, and some of you are quite good at it. A number of folks have written to me during the time that we've had the forum and the blog up asking to help.

Here's something you can do. At my work (Teledyne Brown Engineering) I won a modest amount of internal research and development (IRAD) funding to advance the technology of fluorination of spent nuclear fuel. The time frame is 6-12 months and the funding level is on the order of $100K.

Now I'm not a chemical engineer (and I wish I would have studied chemistry much better in school now) but I know that some of you are.

I would like to put together an experiment that shows how we might take and fluorinate a spent uranium oxide fuel rod. Obviously, we're not going to do this on a real rod at this stage and for this level of funding. We're not even going to be able to use depleted uranium dioxide or something like that. We're going to have to use a simulant.

Looking over the periodic table I quickly surmised that molybdenum or tungsten would probably be the best choices as a uranium simulant, because both of them have volatile hexafluoride species. Neither is a perfect fit--that's understood. But the important thing here is to progress in the right direction towards something that has potential for future follow-on funding.

If you are interested in volunteering your help, and if you have background in these areas, please contact me at kirk.sorensen@tbe.com and tell me what you might like to do. Assume at the outset that innovation you donate will not be yours but will become our intellectual property. Assume that you will not be paid for your efforts. There is a chance that these two caveats may change, especially if you develop something of exceptional quality (heck you might get a job offer from us) but if either of these is a deal-breaker for you, don't contact me.

That said, I would really appreciate any help from anyone who is interested and skilled in these areas.


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PostPosted: Dec 24, 2010 3:55 am 
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Kirk, did you contact the Czech group on fluorination tech? As you're probably well aware they (I think NRIR) have considerable experience and history with it.

http://www.oecd-nea.org/pt/docs/iem/mol ... paper9.pdf


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PostPosted: Dec 24, 2010 8:58 am 
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To avoid wheel-reinvention, the NEA reprocessing overview report for 2010 is a good place to start.


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PostPosted: Dec 24, 2010 10:42 am 
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Hi Cyril, yes I've been in touch with the Czech group (face-to-face) on numerous occasions and they keep trying to tell me that fluorination is more expensive than PUREX because of the cost of the fluorine, which makes no sense to me.


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PostPosted: Dec 24, 2010 12:22 pm 
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Many of the fluorine processing systems do not recycle the fluorine. I believe the czech group used flame fluorine where they went direct from an oxide to UF6. The combination could drive up the cost considerably.

Most use cheaper HF to convert UO2 to UF4. If you follow the path of ore processing you will likely get a fairly cost optimized process (and can look up the costs for conversion from U3O8 to UF6). The question in my mind is what would be the costs for running a very small scale operation like that. For a two fluid, 1GWe, LFTR you might need this to go through 30 m^3 fuel salt with 1 tonne UF4 every six months or so OR 7 liters fuel salt containing 250 grams uranium per hour. According to the wise calculator conversion of 1 tonne uranium from U3O8 to UF6 costs $12,500. IF (a very big if) one can build a very small scale fluorinator as cost efficiently as the big one then you are looking at a cost less than $25,000/year. Note that in LFTR you do not have the U3O8 to UF4 step so you would have savings there but we do add UF6 down to UF4 so some expense there.


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PostPosted: Dec 24, 2010 12:43 pm 
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Lars wrote:
Many of the fluorine processing systems do not recycle the fluorine. I believe the czech group used flame fluorine where they went direct from an oxide to UF6. The combination could drive up the cost considerably.

Most use cheaper HF to convert UO2 to UF4. If you follow the path of ore processing you will likely get a fairly cost optimized process (and can look up the costs for conversion from U3O8 to UF6). The question in my mind is what would be the costs for running a very small scale operation like that. For a two fluid, 1GWe, LFTR you might need this to go through 30 m^3 fuel salt with 1 tonne UF4 every six months or so OR 7 liters fuel salt containing 250 grams uranium per hour. According to the wise calculator conversion of 1 tonne uranium from U3O8 to UF6 costs $12,500. IF (a very big if) one can build a very small scale fluorinator as cost efficiently as the big one then you are looking at a cost less than $25,000/year. Note that in LFTR you do not have the U3O8 to UF4 step so you would have savings there but we do add UF6 down to UF4 so some expense there.


Good points about the conversion plants, they do HF conversion all the time. For the online processing unit the fluorinator wouldn't be necessary. The vacuum still will do as discussed before. But the fluorinator is needed for SNF conversion to fluorides. Which we do need to sell the waste eating argument which might help attract government investment.


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PostPosted: Dec 24, 2010 4:23 pm 
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The INL had a Fluorinel Dissolution Process they operated in the 1980's.
a google search gets you the following:
http://worldwidescience.org/topicpages/ ... ocess.html

Quote:
...The process dissolves irradiated, zirconium-based reactor fuels and adjusts the resultant solution for solvent extraction of uranium in another ICPP facility. ...

Perhaps a view of some of these documents may leads to problems they encountered and solved.

There are people on here who worked on and understand this process.


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PostPosted: Dec 24, 2010 4:51 pm 
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That's very interesting--does anyone have any more information about a Fluorinel Dissolution Process or access to these documents at INL?


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PostPosted: Dec 25, 2010 9:27 am 
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Kirk, could you explain how you are going to grab the transuraniums from spent fuel by fluorinating? Uranium comes out easily along with a bunch of fission products up to niobium probably. These can then be seperated from each other easily by cascaded cold trapping. But PuF6 isn't stable and will radio-lyse to lower valence states that are much less volatile. In fact, HF won't even get you to PuF6 so you need elemental fluorine or perhaps nitrogen fluoride. Perhaps this is why Hitachi is working on their Fluorex process, where they first fluorinate most of the U out and then do solvent extraction on the residual to grab the Pu and some fission products. Electrolysis, metal metal extraction or zone refining will probably be better for that last step though.

I wonder if you can first do HF fluorination and then do a bit of F fluorination to get a staged process where you first remove stable volatile fluorides and then the less stable ones.


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PostPosted: Dec 25, 2010 10:19 am 
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The goal at this stage is simply volume reduction. Remove the 95% of the mass of the spent fuel that is uranium in a way that doesn't "fluff" the waste stream like an aqueous process would. Hopefully remove the uranium from the reactor site and leave the remainder behind awaiting further "regulatory evolution" on the part of the federal government.


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PostPosted: Dec 25, 2010 11:17 am 
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Ok so just U recovery. That's probably a good start. Regarding some more info, the DOE's Information Bridge usually has good documents on a variety of nuclear topics, many are freely accessible. There's a bunch of stuff if you search for Fluorinel.

http://www.osti.gov/bridge/basicsearch.jsp


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PostPosted: Dec 26, 2010 6:25 am 
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Does the IFR electrorefining idea not qualify?

-Iain


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PostPosted: Dec 26, 2010 7:58 am 
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iain wrote:
Does the IFR electrorefining idea not qualify?

-Iain


Sure but you have to go from fluorides to chlorides. Apparently this is the wrong way around since fluorides are more stable. Perhaps electrorefining could be done with fluorides, or chloride volatility could be employed. There hasn't been much work done on either. That cadmium seems like a mess too.

If Kirk just wants to remove U as a first step in the right direction, he could probably just use HF or NF3. Its easier on your equipment. Can use copper, teflon, platinum coatings etc. which doesn't work with pure F. The latter will need diamond and/or frozen salt protection.


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PostPosted: Dec 26, 2010 12:42 pm 
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Kirk,
If you are just removing the uranium then using HF to form UF4 and F2 to form UF6 would follow what ORNL did and likely you could copy equipment used for fuel conversion before enrichment. But wouldn't this path also fluorinate Np? If it does isn't it pretty hard to separate U from Np? Is it OK to mix Np with your uranium?

An alternate path may be to use HF to form UF4 then vacuum distill - likely the Np is still NpF3 which has low volatility. This path would result in some fission products (Cs, and Zr) coming along that would need to be separated out as well. Seems like this should work but I'm cautious since ORNL never mentions this and they were considering using both fluorination and vacuum distilling.

Using a combination of both techniques would isolate your uranium nicely. Using fluorination followed by reduction and vacuum distill would also give you an Np stream - which NASA may want to make their Pu238.

But the main question is why do this? What is the benefit?


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PostPosted: Dec 26, 2010 1:17 pm 
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Actually it should not be too hard to separate NpF6 from UF6, you use different NaF-MgF2 absorber beds as cold trap (sorption-desorption cycles). The Np is valuable as Pu238 precursor and a little other U and Np in it will be no problem for RTGs.

I think it is the fission products that complicate the real world design of a fluorinator. You get Se, Te, I, Tc, Br, Mo, Sb, Ru, Nb. Some with multiple valences. Some will stick with others, eg TcF6 might stick with UF6 in the beds.

But certainly from an energy and long lived wastes perspective we have to grab the transuraniums. Too bad this can't be done with just fluorination.


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