Energy From Thorium Discussion Forum

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PostPosted: Dec 09, 2013 11:11 pm 
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Cyril R wrote:
KitemanSA wrote:
Does _graphite_ suffer all those issues?


Yes, hence the plumbing problem of the two fluid reactor.

With CO2 it would be worse, due to the higher pressure and chemical reaction of CO2 with graphite (C+CO2 = 2CO).
I was under the impression that the plumbing problem was because the graphite shrinks, then grows, under neutron fluence. This does not necessarily mean that the other factor apply, does it?

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PostPosted: Dec 10, 2013 4:22 am 
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What other factor do you mean?


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PostPosted: Dec 10, 2013 7:57 am 
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Cyril R wrote:
What other factor do you mean?
Sorry, a touch of disdigita... factorS.

Quote:
Neutron capture, embrittlement, tritium management, the whole shebang.

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PostPosted: Dec 10, 2013 9:03 am 
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Ok, well then, all of those are still issues. Metals embrittle inside a nuclear reactor. Very special alloys must be used. That has proven to be feasible with water cooled reactors. Unfortunately none of those materials will stand the chemical and thermal environment of a molten salt reactor very long...

The materials that we know will last some time, such as nuclear grade stainless steels, steal a lot of neutrons when they occupy a sizeable fraction of the core of a molten salt reactor. The more because SCO2 is high pressure, needing thick walls. The high pressure also means all sorts of fun things to spend R&D money on, such as irradiation assisted stress corrosion and irradiation assisted thermal creep. It would be a very unforgiving environment.

Internal cooling was considered for molten salt reactors, but only for fast spectra reactors.

It's possible that your concept could work, with advanced composites, likely of the silicon carbide class.


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PostPosted: Dec 11, 2013 12:29 pm 
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Cyril R wrote:
Ok, well then, all of those are still issues. Metals embrittle inside a nuclear reactor. Very special alloys must be used.
??? My statement was about using graphite bajonets to carry SCCO2 thru the core. Now you mention "metals embrittle". How is that related to my post? I am confused.

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PostPosted: Dec 11, 2013 12:40 pm 
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Graphite is no good. It reacts with CO2, and can't take tensile forces from the high pressure of CO2. It is a very weak and brittle material (no ductile failure).

It is the plumbing problem squared.

Only advanced alloys and advanced composites are options. Between the two, only composites offer reasonable neutron economy.


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PostPosted: Dec 11, 2013 6:57 pm 
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Cyril R wrote:
Graphite is no good. It reacts with CO2, and can't take tensile forces from the high pressure of CO2. It is a very weak and brittle material (no ductile failure).

It is the plumbing problem squared.

Only advanced alloys and advanced composites are options. Between the two, only composites offer reasonable neutron economy.
Ok, lets talk about graphite as a simplified term for carbon-carbon composite. CCs are very strong and will crack (slow leak) the matrix before breaking the fiber (fracture).

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PostPosted: Dec 12, 2013 3:23 am 
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Carbon-carbon has poor mechanical properties, it isn't that strong, and it deteriorates rapidly in a neutron flux. Similar corrosion issues as graphite (CO2+C=2CO).

SiC class composites might do, nothing else I can think of will work.


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