Energy From Thorium Discussion Forum

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PostPosted: Jun 02, 2010 8:43 am 
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Luke wrote:
GRLCowan wrote:
......This abstract ...... suggests ZrCl4 could be good for pulling oxygen-in-general to the bottom and making it filterable.


One of the ORNL reports - sorry, haven't got the ref to hand - mentions that they found adding ZrF4 to be helpful in avoiding UO2 precipitation. Traces of oxide always get in, and Zr is a great oxide scavenger since the exchange reaction

ZrF4 + (2/y)MxOy = ZrO2 + (2/y)MxF2y

Strongly favours ZrO2 for most metals M. Even for thorium, it's about 40-50 kJ/mol in favour of ZrO2 and ThF4 vs ThO2 and ZrF4.

I've been wondering about exploiting this for reprocessing schemes, since Zr is a major fission product and ZrF4 is a pain to split out. It forms association complexes with LiF, and follows the FLiBe around. Adding oxide to make ZrO2 would remove it as still bottoms, and zirconia is the perfect waste form for the long half-life zirconium isotopes. Individual zirconia crystals are the oldest identifiable Earthly objects, washed from mountains to redeposit in sandstones that get made into mountains that get re-eroded..... for four billion years. Nothing touches them. Unfortunately, it doesn't work for 1- or 1.5-fluid systems, as the stability against thoria isn't enough when the system has tonnes of thorium and only a few kg of zirconium - you probably hit the thoria solubility limit first, although it would be worth testing to be sure.

I believe ARE used LOTS of ZrF4. I am under the impression that the presence of ZrF4 isn't a big concern except that it continually builds up. The cross-section is around 10x that of the salt so eventually we will want to remove some of it for neutron efficiency but this is far beyond the kg levels. I would guess that we could tolerate a Zr fraction at say 10% of the thorium fraction. Perhaps later in the reactor life we start adding the thorium in as ThO2 and then filter out the solids? We do not generate Zr at the same rate as we add thorium so we would not add all the thorium this way and there is no chance that we will saturate for thorium. Oxygen is generally bad for the reactor - are you confident that ALL of the oxygen will go to Zr and not to U?


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PostPosted: Jan 24, 2015 7:15 pm 
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Can anyone suggest a relatively low (maybe about 500 C) melting eutectic salt that's not particularly volatile or toxic?

Myself and my lab partner have to get some practice in operating our furnace and creating eutectic salt mixtures from solids before we can move on to making FLiNak. I'll be in the lab more melting stuff, so I'd like to have a good salt I can get practice with for basic synthesizing and handling?

Our doctoral student that's over us played around with Na2SO4-NaCl eutectic, but I'm having a bit of a time finding a phase diagram for that.

Any suggestions for salts?

Also, tips on synthesizing and handling of molten salts in general, and FLiNaK in particular are welcomed.


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PostPosted: Jan 25, 2015 4:40 am 
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Vince Hughes wrote:
Can anyone suggest a relatively low (maybe about 500 C) melting eutectic salt that's not particularly volatile or toxic?

Myself and my lab partner have to get some practice in operating our furnace and creating eutectic salt mixtures from solids before we can move on to making FLiNak. I'll be in the lab more melting stuff, so I'd like to have a good salt I can get practice with for basic synthesizing and handling?

Our doctoral student that's over us played around with Na2SO4-NaCl eutectic, but I'm having a bit of a time finding a phase diagram for that.

Any suggestions for salts?

Also, tips on synthesizing and handling of molten salts in general, and FLiNaK in particular are welcomed.


Solar salt is good, NaNO3-KNO3 eutectic. Cheap, non flammable and non toxic, and low melting. Roughly equal bags of each (thats near the eutectic and easy to do), mix as powder together and heat up to 110-120C to evaporate moisture/dissociate hydrate (shouldn't be much), then heat up to 300C or so that should easily start the eutectic melting if you've mixed the powder properly. Don't heat it to over 600C or so, if you're just doing practise then you won't need to go over 350C anyway.

For the fluoride salt I'd recommend KF-ZrF4 rather than FLiNaK. FLiNaK is more corrosive due to the basic nature, and ZrF4 is closer to the use of MSRs - no Li7, Zr is a FP, etc.


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PostPosted: Jan 25, 2015 3:24 pm 
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Thanks Cyril!

I'll look into that and see if they have NaNO3 and KNO3 in stock in the lab. I think they should.

As for using FLiNaK, the entire research is about FLiNaK in particular. Quite a bit of the work is just validation of some of the U of W work on FLiNaK corrosion and candidate materials. Plus the LiF, KF, and NaF have already arrived.


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