Energy From Thorium Discussion Forum

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PostPosted: Jun 23, 2013 8:24 pm 
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With pressure waves, things often happen too fast for the human eye to see....

http://www.youtube.com/watch?v=c3fJRRCAIdk
Periodic Table of Videos
Barking Dog reaction at 3000 frames per second.


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PostPosted: Jul 01, 2013 5:03 am 
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Good. If it's fast, it will be absorbed by the large heat capacity inherent in the fuel salt and graphite. Some 600-700 degree K of subcooling is available, at water-like volumetric heat capacities, a pretty darn good shock absorber. Graphite is also highly resistant to thermal shock.


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PostPosted: Jul 01, 2013 8:50 am 
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The problem is that, unlike the chemical analogue which exhausts itself in a fraction of a second, fission fuel could potentially keep this rapid oscillation going on almost indefinitely -- or at least until the vibrations pulverize the reactor: A few hours at most.

Fortunately, this problem is apparently easily avoided, by avoiding high aspect ratio geometries, and also by constraining bits of fuel to small volumes which cannot transmit pressure waves between them: The equivalent of a squat right cylinder core with many separate fuel channels.


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PostPosted: Jul 01, 2013 5:18 pm 
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If the oscillations are small, it won't matter, at least not with fluoride fuelled reactors. The fluid fuel is the reactor. It can't be pulverized.

The experience with LWRs is that oscillations are always there, and are of concern where a small amount of subcooling is available. The BWR versus the PWR is a good example. BWR has low subcooling at the core inlet and almost no subcooling at the outlet. Because of the large heat capacities involved combined with the negative power coefficient, such reactors can still be designed to be very stable. MSRs are much more tolerant than BWRs. There's no fuel damage to worry about, and one to two orders of magnitude more subcooling.

Still a considerable local temperature differential in the fluid is expected, so an efficient mixing plenum is needed, perhaps partially thermally sleeved on critical locations.


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