Energy From Thorium Discussion Forum

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PostPosted: Apr 10, 2014 1:52 pm 
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From what I recall the MSRE used water filled pipes leading from the drain tank out into the surrounding earth for passive cooling, could you have a number of smaller tanks drain tanks(say a dozen) in a complex under the main reactor tank that used this method.

If it worked for the MSRE on this scale would it also be practical with a commercial sized reactor?


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PostPosted: Apr 10, 2014 7:07 pm 
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Water cooling does not sound like a good idea to me considering what I know about MSRs, the water would flash to steam and potentially burst the pipes. The MSRE may have used water cooling, perhaps it did work, I don't know enough.

Having multiple drain tanks sounds like standard procedure to me. The idea is to divide up the fuel so that there is no longer critical mass to keep the fission going. Dividing up the fuel into multiple tanks also gives greater surface area to cool the fuel. I envisioned a large flat open-top tank with dividers much like an ice tray. The fuel would pour into the tray and overflow pipes from one tank would flow into the next. Once cooled the fuel could be removed as large ingots of frozen salt for processing or disposal.

Reading this thread again I have the idea that the cooling salt could be dumped into the reactor in case of an emergency, as opposed to into the drain tank. Assuming temperatures get too high and there is a failure of the drain system a cooling salt could be dumped in to stop the reaction and reduce the temperature. There would still be a need to drain the tank and/or provide cooling but the immediate issue of ongoing fission and too much heat could be addressed. I will say that this is not a new idea, I saw something similar in a talk about DMSRs by Mr. LeBlanc.

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PostPosted: Apr 10, 2014 9:21 pm 
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From what I recall it was sealed steel tubes with passive conduction of the decay heat into ground with the MSRE.


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PostPosted: Apr 11, 2014 8:24 am 
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I would agree that water should not be incorporated into the design since we do not want any chance of it moderating the fuel salt and restarting the fission process. Also, I think for neutronic reasons that multiple tall small diameter tanks would be used, e.g. 2 m tall and 0.2 m diameter, in order to reduce fissions. The tanks would have an outer liner that uses alloys of cadmium or boron to capture neutrons and keep them from reaching adjacent tanks.

I do think using bars of aluminum to conduct the decay heat from the tanks into bedrock would have merit. The tanks would be fairly small, and using a lot of thick, long aluminum should be able to transfer quite a bit of heat. But it sounds like active cooling would still be the primary heat extraction method.


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PostPosted: Apr 11, 2014 2:47 pm 
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Could someone point me to where MSRE or MSBR were planned to push the decay heat into the ground?
I'm having trouble accepting the concept that we can conduct enough heat in a solid metal pipe to deal with the decay heat.


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PostPosted: Apr 16, 2014 12:53 pm 
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I have not seen a passive system to deal with decay heat from either MSRE or MSBE; I suspect that in those days they were fine with active cooling unlike today where a premium is put on designs that work passively.
The document ORNL-4528 discusses a two fluid reactor design and proposed a drain tank with active cooling using steam. The details can be seen on page 49.
Also, ORNL-4541 discusses a single fluid reactor design and proposed a drain tank with active cooling using a cooled salt stream. The details can be seen on page 85.


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PostPosted: Apr 17, 2014 3:07 am 
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Borax, sodium tetrafluoroborate or a eutectic containing boron salts could absorb heat as well as neutrons. Solids could absorb phase change heat too. In appropriate cladding, they could function as ice-crystals for cooling reactors.


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