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PostPosted: Nov 11, 2012 3:20 pm 
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Lars wrote:
http://en.wikipedia.org/wiki/Fluoride_volatility
With fluoride volatility you get Pu,U,Np boiling at pretty similar temperatures so I'm guessing that they will travel together. But you also have Mo, Tc, Br in the same neighborhood so likely the separation of these from the actinides will be poor from straight fluoridation and then fractional distilling of the gases.

The metals Mo, and Tc want to come out of the salt and will tend to plate out on any cool metal surface where the salt flow is slower.
If the Mo and Tc haven't plated out, then separating the Mo should be easy as the condensation temperature is quite different. The same for Br.

Since the Tc has such a long half life I would just as soon return it to the core with the U. The Wiki article says the the UF6 solidifies and the NpF6 condenses, so a bit of centrifugation should separate those two IF desired. Of course, the temperature sensitivity on that is pretty tight. :mrgreen:

Unless one either puts U238 in the core (a bad idea in my opinion) or returns the Np to the core, there should be little Pu to worry about. And if the little that does get made goes back into the core, so be it.

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PostPosted: Nov 11, 2012 4:12 pm 
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djw1 wrote:
With proper packing and offgas tank(s) design,
we should be able to get close enough to plug flow
so switching tanks is not necessary.
I think this was ORNL's intention.


Even with plugged flow and a long gas travel path, if that works, there´s still a need for isolation valves.


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PostPosted: Nov 11, 2012 6:37 pm 
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KitemanSA wrote:
Lars wrote:
http://en.wikipedia.org/wiki/Fluoride_volatility
With fluoride volatility you get Pu,U,Np boiling at pretty similar temperatures so I'm guessing that they will travel together. But you also have Mo, Tc, Br in the same neighborhood so likely the separation of these from the actinides will be poor from straight fluoridation and then fractional distilling of the gases.

The metals Mo, and Tc want to come out of the salt and will tend to plate out on any cool metal surface where the salt flow is slower.
If the Mo and Tc haven't plated out, then separating the Mo should be easy as the condensation temperature is quite different. The same for Br.

Since the Tc has such a long half life I would just as soon return it to the core with the U. The Wiki article says the the UF6 solidifies and the NpF6 condenses, so a bit of centrifugation should separate those two IF desired. Of course, the temperature sensitivity on that is pretty tight. :mrgreen:

Unless one either puts U238 in the core (a bad idea in my opinion) or returns the Np to the core, there should be little Pu to worry about. And if the little that does get made goes back into the core, so be it.

Agreed it looks like condensing out the Mo, & Br should be effective.
I'd rather not send the Tc back to the core. I can't see it doing any good there. But even if we can't separate it in the fluorination step it should be reasonable to separate as we put things back into clean fuel salt. By controlling the UF3/UF4 ratio before we put the reconstituted salt back into the reactor I think we can cause the Tc to want to come out of solution and settle on some cooled hastalloy surfaces for included for that purpose.
Returning the Np and Pu back to the reactor is fine by me - it reduces the amount of stuff to be burned in a fast reactor later. If you don't want to send it back to the reactor ORNL had a schedule with charcoal beds that would trap the fission product fluorides but allow the UF6 to pass. I wonder what it would do with the plutonium fluorides?
I suspect it will be hard to have both a core with greater than LEU in it and have fluorination facilities present that can separate the uranium from the fission products. Seems like that would make it too hard to win the debate with the proliferation folks. If we have 238U present then we really have to recycle the plutonium back to the core for the neutronics to work out.


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PostPosted: Nov 11, 2012 6:59 pm 
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Personally, I like Kirk's plan for a U238 quick blend where needed but otherwise keep it out.

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PostPosted: Nov 11, 2012 8:26 pm 
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Me too. Now all we have to do is get Kirk to be the final arbiter on the matter.
I also buy the argument that says we only supply these to nuclear states and supply the pre-diluted version to non-weapons states since currently 80% of the electricity is used in weapons or weapons capable states (like Canada, Japan, etc.). But this would be a tough sell as well.


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PostPosted: Nov 12, 2012 4:16 am 
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Guys, guys, could we please go back on topic to discussing the AHTR recent work?


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PostPosted: Nov 12, 2012 8:14 pm 
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Kudos to ORNL. These are heartening studies that are thrilling to read. Thanks to all for the links.


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PostPosted: Nov 12, 2012 11:03 pm 
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Man, I'll have to ask to be put on some sort of mailing list. Looks like this doc has been out at least a month and wasn't aware.

I've been busy at a conference on small reactors here in Ottawa (went very well) and lots of things to catch up on before I can look this over properly. Can someone confirm I'm reading the table right at least. Seems like 1.6 tonnes of fissile to start 1530 MWe (very impressive) and with 2 batches they have a year fuel residence so this means 1.60 tonnes U235 per year? I'm I missing anything?

That is then just over 1000 kg per GWe year which is not bad, a bit better than PWRs and not an awful lot more than the Pebble bed versions are claiming.

David LeBlanc

P.S. Actually I suppose that is just slightly more than the modern PWRs, slightly less than older versions.


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PostPosted: Nov 13, 2012 3:48 am 
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David wrote:
Man, I'll have to ask to be put on some sort of mailing list. Looks like this doc has been out at least a month and wasn't aware.

I've been busy at a conference on small reactors here in Ottawa (went very well) and lots of things to catch up on before I can look this over properly. Can someone confirm I'm reading the table right at least. Seems like 1.6 tonnes of fissile to start 1530 MWe (very impressive) and with 2 batches they have a year fuel residence so this means 1.60 tonnes U235 per year? I'm I missing anything?

That is then just over 1000 kg per GWe year which is not bad, a bit better than PWRs and not an awful lot more than the Pebble bed versions are claiming.

David LeBlanc

P.S. Actually I suppose that is just slightly more than the modern PWRs, slightly less than older versions.


Yes, this is what table 2 says. 17.48 tonnes HM, 9% enrichment, means 1573 kg fissile. With 1530 MWe at a capacity factor of .92 gets 1407 MWe-year, so 1118 kg fissile per GWe-year.

Multi batch refuelling, and going for more thermal spectrum (C/HM of 400), has made this reactor much more fuel efficient, clearly.


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PostPosted: Nov 14, 2012 9:51 am 
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Im entranced by the carbon-carbon core barrel.

The vendors I have talked to admit C-C is
leaky and think they will require considerable R&D to fix this.

Does the design accept the leakage or do they think
they have a non-leaky carbon-carbon?


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PostPosted: Nov 14, 2012 10:07 am 
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djw1 wrote:
Im entranced by the carbon-carbon core barrel.

The vendors I have talked to admit C-C is
leaky and think they will require considerable R&D to fix this.

Does the design accept the leakage or do they think
they have a non-leaky carbon-carbon?


Why is leakage such a stringent demand for the core barrel? There doesn't seem to be much of a driver for leakage, with FLiBe on both sides of the core barrel.

If 1% leaks then 1% coolant at 923 degrees Kelvin is introduced in the core. As opposed to 973 degrees Kelvin. The mixed coolant outlet temperature becomes 972.5 degrees Kelvin in stead of 973.

Seems that you could just accept that leakage (and a lot more in fact) without undue effect on power cycle efficiency. They do that for the DRACS too.


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PostPosted: Nov 14, 2012 11:36 am 
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I agree, but I'm hoping somebody knows
the answer to the question.

A non-leaky C-C would be a very bid deal
in other applications.


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PostPosted: Nov 15, 2012 5:49 am 
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djw1 wrote:
I agree, but I'm hoping somebody knows
the answer to the question.

A non-leaky C-C would be a very bid deal
in other applications.


Okay, I see your point. Anyone here know someone who´s involved in the 3400 MWt AHTR work?

Also, there are some new things in the AHTR work that caught my eye.

The argon cooling system, for example. Now this seems problematic, requiring an active argon cooling system to prevent damage to the concrete silo, this seems like a problem, if not safety then integrity of the plant, during a station blackout. They have some sort of Stirling engine that powers some fans, clever, though is of course still an active component.

Why not just insulate the cavity to the point that cooling is no longer needed? Conduct the heat into the ground. The AHTR document says weight is added with insulation, which seems like a strange argument to make - with 3000 tonnes of FLiBe in the reactor! Surely some light foam or fiber based insulation won´t add much to that.

A 50 cm thick high temp insulation with 0.1 wmk conducts around 100 to 150 Watts-square meter. Much less if reflective coatings are added. Seems that you could just push that 100 Watts out into the ground without getting the concrete over the 80 degree C design value.


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