Energy From Thorium Discussion Forum

It is currently Jan 18, 2018 1:02 pm

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 11 posts ] 
Author Message
 Post subject: Zone refining
PostPosted: Oct 16, 2009 10:33 am 
Offline

Joined: Dec 26, 2007 11:45 am
Posts: 191
Zone refining. Molten salt is poured into a narrow groove on a suitable substrate and allowed to freeze. The salt is then locally heated to create a moving melted zone. After enough passes the strip is analyzed and split into segments. Everything must be carefully designed to stay subcritical, of course.

Has this been considered? I couldn't find any mention in ORNL documents other than some obscure reference from the 50s (apparently this works very well, at least for alkali halides).


Last edited by Owen T on Oct 17, 2009 7:24 am, edited 1 time in total.

Top
 Profile  
 
PostPosted: Oct 16, 2009 12:15 pm 
Offline

Joined: Jan 24, 2007 2:24 pm
Posts: 437
Location: Montreal, Quebec CANADA
The question will be if it will work at all in this case, That's one of the problems with zone refining as a technique - when it works, its amazing, but it doesn't work for all situations.


Top
 Profile  
 
PostPosted: Oct 16, 2009 2:17 pm 
Offline

Joined: Jul 28, 2008 10:44 pm
Posts: 3069
How do we estimate how effective this technique will be?


Top
 Profile  
 
PostPosted: Oct 17, 2009 1:07 am 
Offline

Joined: Jan 24, 2007 2:24 pm
Posts: 437
Location: Montreal, Quebec CANADA
I can see this possibly working to process discharge from a Eutectic Metal Core Reactor, but It would probably have to be determined experimentally if this would be useful for cleaning up salt from a MSR.


Top
 Profile  
 
PostPosted: Oct 17, 2009 7:25 am 
Offline

Joined: Dec 26, 2007 11:45 am
Posts: 191
Lars wrote:
How do we estimate how effective this technique will be?

1. Try to find examples in the literature for separation of fluorides or other halides by zone refining.
2. Go back to basics and the physical principles of crystallization behind it.
3. Try it!


Top
 Profile  
 
PostPosted: Oct 17, 2009 7:33 am 
Offline

Joined: Dec 26, 2007 11:45 am
Posts: 191
DV82XL wrote:
The question will be if it will work at all in this case, That's one of the problems with zone refining as a technique - when it works, its amazing, but it doesn't work for all situations.

If it doesn't work for the raw salt it might work for various distillation fractions or in combination with fractional solidification.
When it works, it really is amazing. It is routinely used for ultrahigh purity materials (e.g. in the semiconductor industry).


Top
 Profile  
 
PostPosted: Oct 19, 2009 12:55 am 
Offline

Joined: Apr 19, 2008 1:06 am
Posts: 2230
DV82XL wrote:
I can see this possibly working to process discharge from a Eutectic Metal Core Reactor, but It would probably have to be determined experimentally if this would be useful for cleaning up salt from a MSR.

Eutectic Metal Core Reactor would be very good for a Fast Spectrum Breeder. It would also have the advantages of a Fluid Fuel Reactor. With both Uranium and Plutonium available in "Waste" fuel, and U238 in depleted uranium, the fuel will not even have to be mined avoiding problems from local residents. If zone refining also works, we are set for power production for centuries.
For uranium poor countries like China, Japan or India the thorium can be substituted for uranium once sufficient fissile feed is available.


Top
 Profile  
 
PostPosted: Oct 19, 2009 2:27 pm 
Offline

Joined: Dec 26, 2007 11:45 am
Posts: 191
DV82XL wrote:
I can see this possibly working to process discharge from a Eutectic Metal Core Reactor, but It would probably have to be determined experimentally if this would be useful for cleaning up salt from a MSR.


Is there anything specific about the crystallization properties of metals vs. those of halide salts that makes them more suitable for zone refining?


Top
 Profile  
 
PostPosted: Oct 19, 2009 3:00 pm 
Offline

Joined: Jan 24, 2007 2:24 pm
Posts: 437
Location: Montreal, Quebec CANADA
Owen T wrote:
Is there anything specific about the crystallization properties of metals vs. those of halide salts that makes them more suitable for zone refining?


That's isn't really the question - this technique works for the system in question, or it doesn't, and to the best of my understanding this has to be determined empirically. Metallic systems do respond well, as I recall.

However I confess that I have not looked at this process closely in many years, and I have not kept up with the literature on the subject, so there may have been work on halide salts that I am not aware of that has been done in the interim.


Top
 Profile  
 
 Post subject: Re: Zone refining
PostPosted: Oct 20, 2009 12:01 am 
Offline

Joined: Jan 24, 2007 2:24 pm
Posts: 437
Location: Montreal, Quebec CANADA
UPDATE:

I found this paper: Fractional Crystallization Reactions in the System LiF-BeF2-ThF4 which backs up what I have been saying about the need to determine the viability of this process for salts experimentally.

Quote:
Since non-equilibrium fractionation of LiF-BeF2-ThF4 melts produces final liquids which are low in thorium, and since the concentrations of rare earths in the solutions are expected to be about 20 ppm at the time when fuel processing is economically mandatory, one might anticipate that a semi-zone refining step might well produce and transport liquids of low thorium concentration and containing a relatively high concentration of rare earths (the solubility of the lanthanide trifluorides in any of the melts one might encounter is almost certainly to be at least 200 ppm at the low temperatures which would be present in this part of the feeder apparatus.)

The efficiency of this concentration step could possibly be impaired seriously if the rare earth trifluorides either formed intermediate compounds (such compounds are formed only for the lanthanides of lighter than Europium ) which interacted with the crystallizing phases or otherwise formed solid solutions with any of the crystallizing phases. The structure of 2LiF-BeF2 and LiFe-ThF4 are known and believed to be incapable of serving as solid state hosts for the rare earth fluorides. The 3LiFe-ThF4 solid solution is an unknown factor in this consideration and could conceivably act as a solvent for lanthanide ions. This possibility as well as the possibility that LiF92ThF4 might also serve as a solid state solvent for lanthanide ions could be examined easily through a small scale laboratory program.


I will note however that much has been done exploring this technique for reprocessing metallic spent nuclear fuels and it does seem practical albeit giving the proliferation nannies conniption fits because it can be used to produce very high purity Pu.


Top
 Profile  
 
 Post subject: Re: Zone refining
PostPosted: Oct 20, 2009 10:25 am 
Offline

Joined: Dec 26, 2007 11:45 am
Posts: 191
DV82XL wrote:
UPDATE:

I found this paper: Fractional Crystallization Reactions in the System LiF-BeF2-ThF4 which backs up what I have been saying about the need to determine the viability of this process for salts experimentally.

Nice find! It shows that while ORNL really left almost no stone unturned. However, the fact that this is a very initial report with no real conclusions means they did not have the resources to pursue all promising directions. There's plenty left for our generation to do... One important direction is to see which advances in materials and other technologies change some of their conclusions but there's work on other directions, too.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 11 posts ] 

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron
Powered by phpBB® Forum Software © phpBB Group