Energy From Thorium Discussion Forum

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PostPosted: Jan 17, 2012 8:52 am 
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I know we'd never use graphite moderation for any chloride system but I am trying to remember if graphite is completely ruled out for use with chloride salts since it would corrode the graphite? Anyone recall offhand? Just wondering if we could ever use any graphite or carbon composite whatsoever, maybe as a liner or for boron carbide absorbers.

David LeBlanc


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PostPosted: Jan 17, 2012 10:10 am 
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There shouldn't be any reaction based on the free energy differences. Carbon tetrachloride is much less stable than any chloride salt used. Maybe the impurities will react. Oxychlorides, and some sulphur mutants, must be quite reactive. But hydrochlorination takes care of them. Redox control is nessary also, just like a fluoride reactor. Chlorides tend to have more oxidation states than fluorides. I don't know if that ends up being problematic in corrosion and processing.


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PostPosted: Jan 17, 2012 10:42 am 
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Cyril R wrote:
There shouldn't be any reaction based on the free energy differences. Carbon tetrachloride is much less stable than any chloride salt used. Maybe the impurities will react. Oxychlorides, and some sulphur mutants, must be quite reactive. But hydrochlorination takes care of them. Redox control is nessary also, just like a fluoride reactor. Chlorides tend to have more oxidation states than fluorides. I don't know if that ends up being problematic in corrosion and processing.



Thanks Cyril, I just had this lingering feeling that someone had mentioned a problem. Stands to reason the interaction would be fine. We'll see if anyone else mentions an issue.

David L.


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PostPosted: Jan 17, 2012 3:49 pm 
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David and Cyril:
I have some good responses to your thread but am quite frustrated with the inability of whatever Software that EfT is using to accept math, chemical & other symbols!

I thus would like to suggest that we continue this and any materials-, chemical- and corrosion-related threads on this Forum built with more robust SW:
Orly Energy Forum – Public side.
Like the Secure side, the Public side of OEF is also not meta-searchable (safer from Foreign comp.) but does not require a signed NDA, as does OEF-Secure.

_________________
–Kim
Kim L. Johnson – ChemInnovar
612.424.2082
KLawrenceJ@gmail.com


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PostPosted: Jan 18, 2012 3:20 am 
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Cyril R wrote:
There shouldn't be any reaction based on the free energy differences. Carbon tetrachloride is much less stable than any chloride salt used. Maybe the impurities will react. Oxychlorides, and some sulphur mutants, must be quite reactive. But hydrochlorination takes care of them. Redox control is nessary also, just like a fluoride reactor. Chlorides tend to have more oxidation states than fluorides. I don't know if that ends up being problematic in corrosion and processing.

It should mean that graphite structures should generally resist corrosion of molten chloride reactors. However, if you need metal parts, they may require SiC lining. Chloride-Graphite compatibility becomes important in molten chloride reactors such as FS-MOS waste digesters.


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PostPosted: Jan 18, 2012 1:27 pm 
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One possible difficulty is that UCl4 boils at 791C / 1atm, which is a bit low for comfort, you don't want the fertile boiing out during an overtemperature incident. So you'd prefer to use mostly UCl3, but I think Cyril pointed out on another thread that U(III) can react with graphite to make uranium carbide. There may well be a reasonable window of UCl3 / UCl4 ratios that is OK for both volatility and graphite reaction, but it would need checking.


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PostPosted: Jan 18, 2012 2:19 pm 
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Luke wrote:
One possible difficulty is that UCl4 boils at 791C / 1atm, which is a bit low for comfort, you don't want the fertile boiing out during an overtemperature incident. So you'd prefer to use mostly UCl3, but I think Cyril pointed out on another thread that U(III) can react with graphite to make uranium carbide. There may well be a reasonable window of UCl3 / UCl4 ratios that is OK for both volatility and graphite reaction, but it would need checking.


So if you use ThCl4 as fertile and startup on PuCl3, with maybe some depleted uranium UCl3/4 for denaturing the bred U233, you'll be fine.

The thorium chloride eutectics are more interesting anyway, as they have lower melting points with very high heavy metal loadings. One of the most attractive is a low melting eutectic of NaCl-ThCl4-PuCl3. Would be interesting to know what happens with additions of UCl3-4.

Due to the lower melting point and viscosity of chlorides compared to fluorides, a chlorides reactor would operate a bit lower in temperature. 600 degrees Celsius salt outlet is probably plenty with the right eutectic.


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PostPosted: Jan 18, 2012 3:38 pm 
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If you are denaturing 233U with 238U you need around 7 atoms of 238U for every 233U. Won't that mean we need to have around equal parts 232Th and 238U as fertile and hence roughly the reactor is 50% 233U and 50% 239Pu?


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PostPosted: Jan 18, 2012 3:55 pm 
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Lars wrote:
If you are denaturing 233U with 238U you need around 7 atoms of 238U for every 233U. Won't that mean we need to have around equal parts 232Th and 238U as fertile and hence roughly the reactor is 50% 233U and 50% 239Pu?


Yes I think that's what you do early on, later stop adding U238 and switch to pure Th-U233 cycle. That way you need less U238 early on, can stop adding it later, and get U232 to take over the isotopic protection of the U233. One of the advantages of very fast spectra is lots of U232, the n,2n that makes U232 being a big neutron energy threshold reaction.


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PostPosted: Jan 19, 2012 10:37 am 
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I forget the reasoning (likely in the Ottewitte papers) but it is always UCl3, not UCl4. I did a quick skim and could not find any discussion of graphite but he does list it as a possible material for his criss-crossing tube concept so chloride salts must be stable with respect to graphite. Good to know, I still think chloride salt systems are a pretty far behind plan B but they do of course have some very desirable attributes.

David LeBlanc


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PostPosted: Jan 19, 2012 11:03 am 
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David wrote:
I forget the reasoning (likely in the Ottewitte papers) but it is always UCl3, not UCl4. I did a quick skim and could not find any discussion of graphite but he does list it as a possible material for his criss-crossing tube concept so chloride salts must be stable with respect to graphite. Good to know, I still think chloride salt systems are a pretty far behind plan B but they do of course have some very desirable attributes.

David LeBlanc


Ottewitte was primarily concerned with corrosion from the 4 chlorines which is of course too much for the fission products to absorb (ie chemically oxidising conditions). However that is a bit of a misinformed thing to say since a three or four percent of UCl3 in the UCl4 gives you the control over this, ie you can have >95% UCl4 from a corrosion protection viewpoint. Ottewitte (or was it Taube?) did say somewhere that the UCl4 was more attractive for its lower melting point, he just used UCl3 for corrosion reasons.

Ottewitte doesn't mention the reaction with U metal on the graphite. ORNL does mention it in the progress reports but it only occurs well over 10% U(III) in the U(IV) which is not necessary for sufficient redox control. A little bit of fertile uranium carbide forming on the graphite would not be a big deal at all but if it is fissile U233 carbide then that could cause a safety issue. Doing a bit of googling, it appears that the reaction is self stopping, the uranium carbide protects further uranium reacting. However uranium metal also reacts with most metal alloys so you don't want to make it in your reactor.


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