Energy From Thorium Discussion Forum

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PostPosted: Dec 01, 2012 5:40 am 
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It would be interesting to figure out how much recombination could occur with surfaces coated in platinum. A forced system would likely still be required though as most of the fuel solution is not in contact with the container.


But the heat exchanger is. This design still uses a heat exchanger, right? Using the pool water as secondary fluid? Or are you planning on such a low power density core fluid that it simply conducts heat through the container?

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During prompt transients radiolytic gas can form almost instantly and create a pressure burst in the solution reaching up to 100 psi if a period of less than ~10 ms are attained. It causes big swings in reactivity as the gas is instantly produced, causes a large instant negative reactivity insertion, the gas then migrates to the surface and out of the solution, the reactivity then rises back up quickly and causes another power spike. This cycle continues with smaller and smaller oscillations in power until the temperature coefficient can stabilize the overall reactivity.

This occurs with transient periods up to ~20 seconds. However the radiolytic gas has less and less of an effect on the transient as you start with a larger and larger initial period.


Perhaps you could use a compensating liquid column (U-tube) with one leg connecting the core and the other having an expansion gas chamber on top.


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PostPosted: Dec 04, 2012 9:26 pm 
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Cyril R wrote:
But the heat exchanger is. This design still uses a heat exchanger, right? Using the pool water as secondary fluid? Or are you planning on such a low power density core fluid that it simply conducts heat through the container?

This reactor will only be rated at 20 kWt so passive natural convection should supply all the cooling necessary (there is a small heat exchanger to keep the bulk pool water cool on extended full power reactor runs though). However, during transients consisting of a sudden step insertions of the maximum available excess reactivity (~+5.8 mk @ 20*C), natural convection may not be capable of keeping the fuel solution <100*C. It may be close. I will actually be performing non-nuclear tests on a to-scale mock up of the reactor up at CRL early next year, so I will see how close my model is to reality.

Cyril R wrote:
Perhaps you could use a compensating liquid column (U-tube) with one leg connecting the core and the other having an expansion gas chamber on top.

There will likely be a gas tube connecting to the top of the reactor to act as a sort pressure cushion for fuel solution thermal expansion. With a minimum period of ~1 second, pressure bursts from rapid radiolysis should factor in in the worst case reactivity insertion for this reactor.

It is a simple design with not much to it which is its selling point. A university could install one of these, use it for regular research requirements and also produce medical isotopes as a source of income for the department/school with minimally trained staff.


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PostPosted: Dec 10, 2012 6:43 pm 
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All types of reactors may have their uses but the real choices in fluid fuel power reactors are:-
1. Thorium (Abundant in earth) Vs uranium fuel. A lot of uranium is in stocks of used fuel and depleted uranium needing disposal.
2. Fast spectrum (can use uranium or thorium as a breeder) Vs thermal which could be a breeder with thorium only.
3. Fluoride salts (already tried experimentally) Vs Chloride salts (generally lower melting/boiling).


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PostPosted: Aug 29, 2013 6:11 am 
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In the fast spectrum, Manganese-Uranium forms MnU6 with an eutectic point of 720C and with a lower corrosion effect than Uranium metal. At 850C the fuel can be loaded and unloaded as a melted metal.


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PostPosted: Aug 29, 2013 7:14 am 
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I really do like aqueuous homogenous reactors for certain non electricity production uses.
They allow for fuel recycling without the horrendous problems of small scale PUREX plants (handling radioactive acidic solutions) but they would also allow low pressure steam for MED use to be generated (as such steam can be below atmospheric pressure and at only about 350K if required).

Someone will have seen my proposal to use an AHR to fission Curium from MOX and UOx LWR fuels?


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PostPosted: Oct 29, 2013 7:55 pm 
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Do "Liquid Metal Fueled Reactors" really constructed in history?


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PostPosted: Oct 30, 2013 3:25 am 
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longwei1221 wrote:
Do "Liquid Metal Fueled Reactors" really constructed in history?


Yes, the LAMPRE - Los Alamos Molten Plutonium Reactor Experiment - was fuelled by molten plutonium-iron eutectic. It was cooled by sodium. Kind of scary, but it was built and worked.


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PostPosted: Oct 30, 2013 4:40 am 
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Time has come when cost of reactors is a major consideration. In the US, the reactors are giving way to cheap gas. In W. Europe, disposal of used fuel is a major factor. Overnight costs are ~$7000/kW. China is going ahead with lower costs. The nuclear power requires following developments to compete:=
1. Cheaper reprocessing of used fuel. Chloride/Fluoride volatilisation to recover most of uranium to reduce the material for processing is a necessary preliminary. The rest can be electrolyzed in salt solution.
2. Liquid fuel to reduce fuel fabrication and processing costs. Part of fertile including the blanket can be metallic thorium to reduce quantity of salt and reactor size.
3. Secondary coolant to transport heat from core could be safe molten metal lead.
4. Fast spectrum for compact core size.
5. As high temperature as feasible for higher thermal efficiency.
Work could start with U238-Pu239 fuel cycle and continue with U233 fissile which can be recovered by electrolysis.


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PostPosted: Oct 31, 2013 8:28 pm 
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Cyril R wrote:
longwei1221 wrote:
Do "Liquid Metal Fueled Reactors" really constructed in history?


Yes, the LAMPRE - Los Alamos Molten Plutonium Reactor Experiment - was fuelled by molten plutonium-iron eutectic. It was cooled by sodium. Kind of scary, but it was built and worked.


In LAMPRE, should molten plutonium fuel be isolated from liquid sodium?
Is liquid metal core similar to Aqueous Homogeneous Reactor in principle?


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PostPosted: Nov 01, 2013 3:16 am 
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longwei1221 wrote:
Cyril R wrote:
longwei1221 wrote:
Do "Liquid Metal Fueled Reactors" really constructed in history?


Yes, the LAMPRE - Los Alamos Molten Plutonium Reactor Experiment - was fuelled by molten plutonium-iron eutectic. It was cooled by sodium. Kind of scary, but it was built and worked.


In LAMPRE, should molten plutonium fuel be isolated from liquid sodium?
Is liquid metal core similar to Aqueous Homogeneous Reactor in principle?


Plutonium is chemically compatible with sodium, and if I recall correctly, the mutual solubility is nil. So strictly speaking, the coolant and fuel are more compatible with each other than LWRs (UO2 reacts with hot water). Of course you want to isolate most of the fission products so there must be seperation, unless you don't care running the sodium loop at absurd radioactivity levels (I would worry about this, even just Na-24 is bad enough already).

In LAMPRE, it looks like they used fuel assemblies of some sort, so this was basically an internally cooled liquid fuel reactor (so not pumping the molten plutonium around, you don't want to be doing that, it is too scary).

So it's not that similar to aqeous homogeneous reactors, in that it has no external cooling of the fluid fuel, but more traditional fuel assemblies inside the core.


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PostPosted: Nov 01, 2013 10:55 am 
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It appears to be essentially the ultimate in vented fuel assemblies.


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PostPosted: Nov 01, 2013 11:20 am 
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E Ireland wrote:
It appears to be essentially the ultimate in vented fuel assemblies.


Yes, very little of the gas will remain in the fuel rods if the fuel is liquid. In fact, neither U nor Pu metal is volatile, so this offers an option to remove all volatiles online. One can even imagine putting the fuel rods under mild vacuum, to assist in the volatiles removal. Very low source term plus better neutron economy, without actually processing the fuel.


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PostPosted: Nov 01, 2013 3:39 pm 
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Cyril R wrote:
E Ireland wrote:
It appears to be essentially the ultimate in vented fuel assemblies.


Yes, very little of the gas will remain in the fuel rods if the fuel is liquid. In fact, neither U nor Pu metal is volatile, so this offers an option to remove all volatiles online. One can even imagine putting the fuel rods under mild vacuum, to assist in the volatiles removal. Very low source term plus better neutron economy, without actually processing the fuel.

Over the life of the fuel rod how much space will the gas require to remain at a low pressure?


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PostPosted: Nov 01, 2013 3:44 pm 
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Who needs sealed rods? Just allow the volatiles to vent from the top. Vacuum distillation continuously.


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PostPosted: Nov 01, 2013 3:49 pm 
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E Ireland wrote:
Who needs sealed rods? Just allow the volatiles to vent from the top. Vacuum distillation continuously.


That's the idea here, yes. One could deliberately connect a vacuum vessel to the fuel rods. Purge the volatiles and condense and trap them in some place away from the reactor, with passive cooling, double containment and shielding.


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