Energy From Thorium Discussion Forum

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PostPosted: Aug 03, 2014 4:56 am 
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Having just watched Dr Boyd's presentation at TEAC6 on youtube, I'm curious what the performance of ThCr is likely to be in contact with molten salts; if a suitable corrosion resistant alloy was found it could potentially make mass production of modular MSRs a lot cheaper. Even if not it seems to present possibilities for existing nuclear plants, as durability of boiler tubes in either steel or stainless steel is an ongoing maintenance challenge.

Like he says, there's a mountain of PhDs waiting to be written here to discover what's what.


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PostPosted: Aug 04, 2014 1:19 pm 
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I think Dr. Boyd's chief point is just how under-researched these materials are. The research that we DO have seems to suggest ThCr would be a cheap and superior alternative to most ubiquitous stainless steels, which is an enormous market.


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PostPosted: Aug 04, 2014 11:35 pm 
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Both chromium and thorium will dissolve in fluoride salts so I doubt a thorium-chromium alloy would make a good vessel (unless it forms a self-protecting film like aluminum does in oxygen). But I'd agree that there is a lot of room to explore. Though, I don't like the idea of using a fertile material to make a vessel out of when there are neutrons flying around. It means you will be having fission happening inside your vessel walls!!


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PostPosted: Aug 04, 2014 11:41 pm 
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Th and Cr have considerable neutron absorption. Would be useful materials only outside the reactor core.


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PostPosted: Aug 05, 2014 1:28 am 
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Uranium alloys have always suffered from swelling from solid-solid phase transitions at relatively low temperatures. Adding some zirconium helps but its not a complete solution. The IFR type reactor is the only reactor that can use it as it uses a sodium filled gap between the uranium fuel and the cladding.

Thorium doesn't go through these solid-solid phase transitions until very high temperatures. So, its more stable. The chromium would protect against oxidation but you'd need quite a bit of it. It wouldn't work in a fluoride environment because both thorium and chromium fluorinate and both thorium and chromium fluoride are soluble in the salt. If the salt is kept reducing, dissolution rates are slow. But, uranium and protactinium will dissolve so you still get fissile and fission in the coolant salt. You'd still need a cladding to make an AHTR type reactor.

So, what is the advantage for MSRs? I don't really see it to be honest. If a reliable and durable coating (maybe nickel) can be applied to the thorium then you'd not need chromium and you might be able to make an AHTR. Problem is, coating failure would make it an MSR again.

In terms of structural applications thorium is not that attractive. It isn't actually very strong, and why would you want to use it over superalloys or just simple austenitic stainless steel?


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PostPosted: Aug 05, 2014 9:53 am 
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Cyril R wrote:
Uranium alloys have always suffered from swelling from solid-solid phase transitions at relatively low temperatures. Adding some zirconium helps but its not a complete solution. The IFR type reactor is the only reactor that can use it as it uses a sodium filled gap between the uranium fuel and the cladding.

Thorium doesn't go through these solid-solid phase transitions until very high temperatures. So, its more stable. The chromium would protect against oxidation but you'd need quite a bit of it. It wouldn't work in a fluoride environment because both thorium and chromium fluorinate and both thorium and chromium fluoride are soluble in the salt. If the salt is kept reducing, dissolution rates are slow. But, uranium and protactinium will dissolve so you still get fissile and fission in the coolant salt. You'd still need a cladding to make an AHTR type reactor.

So, what is the advantage for MSRs? I don't really see it to be honest. If a reliable and durable coating (maybe nickel) can be applied to the thorium then you'd not need chromium and you might be able to make an AHTR. Problem is, coating failure would make it an MSR again.

In terms of structural applications thorium is not that attractive. It isn't actually very strong, and why would you want to use it over superalloys or just simple austenitic stainless steel?


Dr. Boyd noted ThCr (2% Cr) has double the tensile strength of SS316 and is non-magnetic, ductile/workable, high temperature tolerance.

http://youtu.be/XzevZh7iKao


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PostPosted: Aug 05, 2014 10:53 am 
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I have the following data.

Ss316: 515 mpa uts
Th-2cr: 360 mpa uts

For annealed heats.

Price wise th-2cr competes with superalloys not with ss. Thats no win.


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PostPosted: Aug 05, 2014 3:47 pm 
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Cyril R wrote:
I have the following data.

Ss316: 515 mpa uts
Th-2cr: 360 mpa uts

For annealed heats.

Price wise th-2cr competes with superalloys not with ss. Thats no win.


You're numbers look right. The chart he shows in the video lists ~52,000 psi, which is 360 megapascals. That's a long way off from his claims, I wonder if there is a different formulation he didn't give data for. Why is Th-Cr so expensive, is that just a function of the low demand for it? I'd think it could be made cheaply considering that Th is abundant in iron ore tailings and it's easy to work with.


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PostPosted: Aug 05, 2014 5:38 pm 
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Cthorm wrote:
Cyril R wrote:
I have the following data.

Ss316: 515 mpa uts
Th-2cr: 360 mpa uts

For annealed heats.

Price wise th-2cr competes with superalloys not with ss. Thats no win.


You're numbers look right. The chart he shows in the video lists ~52,000 psi, which is 360 megapascals. That's a long way off from his claims, I wonder if there is a different formulation he didn't give data for. Why is Th-Cr so expensive, is that just a function of the low demand for it? I'd think it could be made cheaply considering that Th is abundant in iron ore tailings and it's easy to work with.


He had only a few minutes to do his talk, it was obvious that Boyd wanted to tell more than he had time for. Reading between the lines, he could be talking about cold worked thorium, which would increase the tensile strength. This is also possible with austenitic SS but it can make it slightly magnetic which is what Boyd said he didn't want (strong magnetic applications). Boyd mentioned thorium can be cold worked a lot, perhaps more than 50% cold working woul be acceptable and it shouldn't become magnetic.

For MSRs that isn't relevant because we don't care about magnetic permeability (excepting a few special applications such as canned rotor pump rotor housings if we use these). Plus, cold work benefits are lost at high MSR temperature. In any case, cold work is a compromise: you get greater tensile strength but the ratio of tensile to yielding becomes smaller (less ductile, less elongation) so that is a downside.

On cost, best case scenario, if thorium production goes up greatly, and we stup fussing about microsieverts, then yes it could get many times cheaper. Likely it would be on par with lead - think $2/kg or so. I'm not really sure if it would matter because the refs from Boyd are from the 50's when people cared less about radioactivity fuss. My guess is this material isn't very easy to work with - quite chemically reactive (Th wants to be ThO2) that would increase cost of refining, over say lead which is low melting and doesn't really want to be an oxide. Then there's the purity issue. Th likes the rare earths a little bit too much. So perhaps rare earths provide a more reasonable price bracket. If that's the case then it doesn't look so good. Yttrium, neodymium, etc. these are all costly. There is currently no demand for thorium so that pushes price down. But then again its demand is so low as to make it a specialty metal which increases price again... hard to say.

I should point out also that stainless steel is mostly iron. There is no way , no way that thorium will ever be cheaper than iron.


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PostPosted: Aug 07, 2014 8:57 am 
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Cyril R wrote:
It wouldn't work in a fluoride environment because both thorium and chromium fluorinate


So what about those nickel-alloys then? They contain quite a bit of chromium. Why aren't they affected?


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PostPosted: Aug 07, 2014 9:46 am 
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Gilliam wrote:
Cyril R wrote:
It wouldn't work in a fluoride environment because both thorium and chromium fluorinate


So what about those nickel-alloys then? They contain quite a bit of chromium. Why aren't they affected?


They are affected. The chromium will preferentially leach from the surface. However, the remaining nickel-rich substrate provides protection against further attack, so the attack rate is greatly reduced over time (controlled primarily by high temperature diffusion of chromium from deeper in the alloy up to the surface). Thorium provides no such protection because it wants to fluorinate even more than chromium!

In FLiBe, chromium doesn't fluorinate much, but thorium fluorination rate should still be quite high. So, 2% chromium should not protect it. Coating with nickel would be much more effective, but how long does the coating last? Thorium would eventually diffuse through or the coating would spall off or erode.


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