Energy From Thorium Discussion Forum

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PostPosted: Nov 01, 2013 6:06 pm 
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Cyril R wrote:
condense and trap them

Perhaps a nitpick. Certain condensing many of them is fine but the noble gases are rather tough to condense.


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PostPosted: Nov 01, 2013 7:10 pm 
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Lars wrote:
Cyril R wrote:
condense and trap them

Perhaps a nitpick. Certain condensing many of them is fine but the noble gases are rather tough to condense.


Well of course, the noncondensables could be compressed in a tight volume, but before we compress those noncondensables, it is good to condense the condensables in a cold trap (this would also be the solids trap as some particles would freeze out, like CsI, plus noble metal particles). Then passively gravity drain the condensate over reaction traps to bind up the cesium and iodine to something stable and nonvolatile (make CsF and AgI as we discussed before).


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PostPosted: Nov 01, 2013 9:10 pm 
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We don't want the gases to leave the reactor too quickly. They are pretty hot and the reactor core is has an ample cooling system. If we pull the gases out within a minute they will generate some 20MW!
I think we generate around 1000 moles of gas per year. So if we want to keep the gas on average for an hour before we pull the gas out we need to store around 6 liters of gas in the reactor core at 1 atm/600K.


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PostPosted: Nov 02, 2013 12:41 am 
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Iodine will likely trap in the reactor as Uranium, Plutonium or Iron Iodides, I don't know about the BP of the Former two but the latter apparently doesn't boil till going on 1100K.
The fuel elements will be at a great deal hotter than 600K remember, since that is the approximate temperature of the coolant itself.

And 20MW is not really that much when you think about it (is that for a multi-gigawatt reactor?)
You aren't handling it diluted with vast amounts of spare gas as in an LFTR design remember.


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PostPosted: Nov 02, 2013 12:45 am 
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20MWatts is plenty if you have it in gas form in 6 liters!
But the reactor core has a fantastic cooling system that can literally move gigawatts so that is a convenient place to keep this hot stuff until it cools a bit. As to the temperature of the gas - I would guess the gas has much better thermal conductivity than uranium oxide so it should not be at the same temperature as the interior of solid fuel rods.


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PostPosted: Nov 02, 2013 1:03 am 
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What about just holding the gas in the channels of a PCHE?
That gives you the gas transfer you need (and 20MWt in 6L really is alot :shock: ).

No reason to hold it in the reactor really apart from a slight operational convenience, but remember that those FPs makes up a large fraction of your shutdown thermal output so there are operational advantages to removing it.
It allows you to seperate the heat load from all the nasty actinides in a SCRAM situation.


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PostPosted: Nov 02, 2013 3:28 am 
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Lars, are you sure the 20 MWth is in the 6 liters? 20 MWth is the long term equilibrium. I don't think the reactor makes 20 MWth from operating just one hour, right?

Also under mild vacuum the 6 liters would be more like 600 liters. Like Ed says, it could be stored in a PCHE as temporary storage. 600 liters would be around 2-3 m3 PCHE. Only 10 MWth/m3. A passive condensables drain in this PCHE will then drain to the immobilization traps. The other stream side could be a clean fluoride salt operating in natural circulation. PCHE in a tub of buffer salt or some other inert high temp liquid.


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PostPosted: Nov 02, 2013 10:19 am 
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Cyril R wrote:
Lars, are you sure the 20 MWth is in the 6 liters? 20 MWth is the long term equilibrium. I don't think the reactor makes 20 MWth from operating just one hour, right?

Also under mild vacuum the 6 liters would be more like 600 liters. Like Ed says, it could be stored in a PCHE as temporary storage. 600 liters would be around 2-3 m3 PCHE. Only 10 MWth/m3. A passive condensables drain in this PCHE will then drain to the immobilization traps. The other stream side could be a clean fluoride salt operating in natural circulation. PCHE in a tub of buffer salt or some other inert high temp liquid.

Calculation errors are always possible. Here is how I came up with the number. I started with 1000 moles of gas produced per year. We can sanity check that since we fission approximately 1000kg/year, that would be around 4000 moles/year, so this would mean the fission yield around 25% for all the gas - which is in the right neighborhood.
1000 moles / year * (1/365/24 years/hour) * (22.4 liters/mole * 600/273) = 5.6 Liters per hour at 1ATM, 600K.

As for the power, ORNL 4541 pg 85 says "The decay heat load in the drain tank, estimated to be about 18 MW ... " [Edit] I should note this is for a 2 hour holding tank so roughly 12 liters of gas.

Interesting thought to use the vacuum to increase the volume as well as to pull the gases out of the fuel salt.


Last edited by Lars on Nov 02, 2013 8:04 pm, edited 1 time in total.

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PostPosted: Nov 02, 2013 2:19 pm 
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Another advantage with vacuum is that leaks to the outside become impossible. That's a big advantage when you're handling absurdly radioactive and mobile offgas. Even then a double walled containment with leak detection in the gas annulus is a good idea IMHO.


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