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 Post subject: SC CO2 Reactor?
PostPosted: Apr 13, 2016 9:36 am 
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Has anyone examined the use of supercritical CO2 as both the working fluid and the moderator for a reactor?

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 Post subject: Re: SC CO2 Reactor?
PostPosted: Apr 13, 2016 9:48 am 
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Is there some reason you want a high-pressure reactor?

Haven't we all learned our lesson on that one?


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 Post subject: Re: SC CO2 Reactor?
PostPosted: Apr 13, 2016 10:39 am 
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One of the main problems is that CO2 has a low moderating power even in the liquid state which has the highest density. You will need a lot of CO2 to "thermalize" a significant amount of neutrons. That means a big pressure vessel (or a big pre-stressed concrete structure).

The CO2 cooled reactors generally use a separate moderator (graphite, heavy water) or are fast reactors (like this one :
http://energyfromthorium.com/forum/viewtopic.php?f=56&t=3524 ).


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 Post subject: Re: SC CO2 Reactor?
PostPosted: Apr 13, 2016 5:51 pm 
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Kirk Sorensen wrote:
Is there some reason you want a high-pressure reactor?

Haven't we all learned our lesson on that one?


Well, the idea was that a very small turbine close coupled to a small core might be a very nice thing to have. And high pressure is well known. Besides, the only high pressure would need to be in the coolant pipes, not the core vessel. Yes, it is nice to have low pressure, but with the moderator being the working fluid, perhaps we could keep the delayed neutrons in the core where they would help with stability. But if the pipes woud need to be very large to make the moderation work, perhaps a pressure hull with same gage pressure working fluid would be better neutronically.

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 Post subject: Re: SC CO2 Reactor?
PostPosted: Apr 14, 2016 2:56 am 
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Total left field idea, but a pool type reactor with direct bubbling of sCO2 through the pool liquid and captured by a bell under the pool nominal liquid surface. Pool/containment is nominally at atmospheric.


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 Post subject: Re: SC CO2 Reactor?
PostPosted: Apr 14, 2016 11:44 pm 
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Asteroza wrote:
Total left field idea, but a pool type reactor with direct bubbling of sCO2 through the pool liquid and captured by a bell under the pool nominal liquid surface. Pool/containment is nominally at atmospheric.

SC CO2 does not exist at atmospheric pressure.

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 Post subject: Re: SC CO2 Reactor?
PostPosted: Apr 15, 2016 5:38 am 
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Kirk Sorensen wrote:
Is there some reason you want a high-pressure reactor?

Haven't we all learned our lesson on that one?

But I WOULD like to see a low pressure reactor. We cannot put all our eggs in a tub of corrosive salt fuel either. At least for heat transfer we need a low pressure heat transfer fluid. Would be really nice if it can replace graphite as moderator too.


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 Post subject: Re: SC CO2 Reactor?
PostPosted: Apr 18, 2016 3:41 am 
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KitemanSA wrote:
Asteroza wrote:
Total left field idea, but a pool type reactor with direct bubbling of sCO2 through the pool liquid and captured by a bell under the pool nominal liquid surface. Pool/containment is nominally at atmospheric.

SC CO2 does not exist at atmospheric pressure.


Yes, I am aware of that. Saying a sealed capture bell stuffed into the top of the pool to capture the bubbles might work. The pressure of sCO2 would force down the head of liquid in the bell, which has to fight the head of the rest of the liquid in the pool rising but otherwise exposed to atmospheric pressure. Considering most liquid coolants are metals/salts that are heavy, the rise of the pool itself might not be that large depending on the configuration.


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 Post subject: Re: SC CO2 Reactor?
PostPosted: Apr 18, 2016 11:35 am 
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What?

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 Post subject: Re: SC CO2 Reactor?
PostPosted: Apr 18, 2016 1:26 pm 
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I have heard tales that 13C is actually a better moderator than 12C, anyone have any capture/scattering data about that?


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 Post subject: Re: SC CO2 Reactor?
PostPosted: Apr 18, 2016 6:42 pm 
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Quote:
I have heard tales that 13C is actually a better moderator than 12C, anyone have any capture/scattering data about that?


There are several websites with cross section libraries. For example the Evaluated Nuclear Data Files :
https://www-nds.iaea.org/exfor/endf.htm

13C thermal capture cross section is around 2.5 times smaller than 12C. Concerning elastic scattering they are equivalent and 12C is around 2.5 times better for inelastic scattering (if I picked the good data).


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 Post subject: Re: SC CO2 Reactor?
PostPosted: Apr 18, 2016 9:14 pm 
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So its either comparable or much better depending on which scattering regime is dominant?
Interesting.


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 Post subject: Re: SC CO2 Reactor?
PostPosted: Apr 19, 2016 1:02 am 
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'So its either comparable or much better depending on which scattering regime is dominant?
Interesting.'
Not really. Ordinary hydrogen has an absorption cross section about 600 times larger than deuterium, and about ten times the scattering cross section. Lithium 6 has 20,000 times the absorption cross-section of Li7. Carbon is pretty good already, and C13 would be expensive and of little benefit.


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 Post subject: Re: SC CO2 Reactor?
PostPosted: Apr 20, 2016 12:49 am 
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KitemanSA wrote:
What?


Hrm, I'm not very familar with the terminology, but I believe this would be called a sparge type direct contact heat exchanger. Arranging the column such that hot liquid salts can enter the column below the nominal column liquid/gas surface safely so sCO2 can't escape out to the unpressurized pool surface should be doable. Think of those air domes for divers to escape to that are anchored to the sea floor.


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 Post subject: Re: SC CO2 Reactor?
PostPosted: Apr 20, 2016 6:11 am 
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If a stupid idea like this is what the forum wants to talk about then maybe it's time to totally shut down this form. Topic locked.


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