Energy From Thorium Discussion Forum

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 Post subject: Re: A better coolant!
PostPosted: Sep 28, 2010 1:10 am 
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(n,gamma) is the neutron capture cross-section - that is the one we worry about - unless your talking about a fertile atom.

(n,elastic) is where the neutron bounces off giving up momentum to the atom in a manner similar to colliding balls. This is typically the largest cross-section in the epi spectrum. It is part of what determines how effective a moderator something is.

(n,inelastic) is where the neutron is momentarily captured excites atom into a higher energy state. As such a (n,inelastic) reaction commonly will absorb more energy from the neutron than an elastic collision.


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 Post subject: Re: A better coolant!
PostPosted: Sep 28, 2010 6:59 am 
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Of the coolants currently in use, water is highly volatile creating risk of LOCA. This was a problem both at TMI and Chernobyl. It also absorbs neutrons creating a requirement of enriching uranium. Heavy water is very costly and also volatile. Sodium is highly fire prone.
FLiBe is a better coolant but an average moderator requiring additional moderator for thermal reactors. It has been proposed as a coolant for AHTR.
AlMg eutectic
Is non volatile like sodium and FLiBe.
Melting point comparable to FLiBe.
Less fire prone than sodium.
Lower neutron absorption than light water or sodium.
Less costly compared to heavy water.
It is not a moderator.
More benign to reactor materials than FLiBe.
I think it needs a chance.


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 Post subject: Re: A better coolant!
PostPosted: Sep 29, 2010 10:42 pm 
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The use of Gallium was modeled for feasibility by some Russian workers as a basis for a plutonium fueled Homogeneous Reactor. I came out just like a MSR.

If a fast reactor will work, of thermal reactor will surely work also.

http://www.sciencedirect.com/science?_o ... archtype=a


Quote:
Gallium-cooled liquid metallic-fueled fast reactor

We have examined the effects on core characteristics of using two different types of Pu-based metallic alloy fuels in the gallium-cooled fast reactor core. In the proposed concept, the liquid metal fast nuclear reactor uses metallic fuel in the liquid phase and gallium coolant at high temperature (inlet 1700K, outlet 1900K). The liquid fuel is continuously supplied to the reactor during operation at full reactor power. The reactor power is controlled by rotational control drums with absorber material. The aim was to evaluate reactor core neutronics and safety characteristics demonstrating a feasibility of the reactor system. Although gallium has large absorption cross section in the high neutron energy region, we can design the core with rather good neutronics performances. The large negative reactivity feedback induced by the thermal expansion of liquid metallic fuel ensures the core's inherent safety against the unprotected loss-of-flow transient.


Also:


http://www.sciencedirect.com/science?_o ... archtype=a


Quote:
A concept of a long life multipurpose nuclear reactor with self-sustained liquid metallic fuel is proposed to meet the requirements for the future energy production. The conceptual design is described and the core neutronic characteristics are obtained based on two-dimensional cylindrical diffusion reactor model. The influence of fission products separation in the liquid-fueled system on the core burnup capability is discussed. The burnup analysis shows a feasibility of the long life refueling-free core concept.

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 Post subject: Re: A better coolant!
PostPosted: Dec 18, 2011 11:36 am 
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Suprisingly, gallium is more abundant than lead! This makes it much more attractive than I previously thought.

Though todays production rate is only tens of tonnes per year.

http://en.wikipedia.org/wiki/Abundance_ ... %27s_crust

Gallium could be an option for the secondary coolant, if it used TZM/molybdenum or C-SiC tubing for the heat exchanger.

It would also be a nice option for the DRACS cooling system that Per Peterson wants to put on his PB-AHTR for ultimate heat removal. The low freezing temperature, high surface tension preventing small crack diffusion, and nearly zero reaction with water and air (outside environment) is really great for this application. And you don't need so much coolant for the DRACS.

Similarly, Jaro's HW-MSR uses decay heat cooling coils where gallium would be a promising coolant, ticking all the boxes.


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 Post subject: Re: A better coolant!
PostPosted: Dec 18, 2011 12:30 pm 
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According to this presentation, gallium coolant is compatible with titanium and stainless steel, though the latter is hard to believe unless it is Si/Ti/Zr enhanced stainless steel. Looks interesting.

http://www.indiana.edu/~lens/UCANS/Meet ... _11_20.pdf


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 Post subject: Re: A better coolant!
PostPosted: Dec 18, 2011 3:25 pm 
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Location: Columbia, SC
MSDS

http://www.scholarchemistry.com/msds/Gallium_Mtl.pdf


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 Post subject: Re: A better coolant!
PostPosted: Dec 18, 2011 4:44 pm 
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USPWR_SRO wrote:


Thanks, interesting. Looks like standard MSDS exaggerated ass-cowering to me. Handling it as you would handle lead is conservative enough. I'd worry a lot more about soluble fluorides toxicity. And I don't worry about those much at all.


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 Post subject: Re: A better coolant!
PostPosted: Dec 19, 2011 9:11 am 
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Gallium has a much higher neutron absorption as compared to Na or Pb (1 order of magnitude). It can, therefore only be used outside the core.
Ref-Neutron News, Vol. 3, No. 3, 1992, pp. 29-37.


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 Post subject: Re: A better coolant!
PostPosted: Dec 19, 2011 9:39 am 
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jagdish wrote:
Gallium has a much higher neutron absorption as compared to Na or Pb (1 order of magnitude). It can, therefore only be used outside the core.
Ref-Neutron News, Vol. 3, No. 3, 1992, pp. 29-37.


Yes, that's why I mentioned secondary coolants and DRACS piping coolant as possible applications.


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