[extropy-chat] Energy & Global Warming [was: Partisans and EP]

Eugen Leitl eugen at leitl.org
Sun Feb 11 20:16:38 UTC 2007

On Sun, Feb 11, 2007 at 10:37:24AM -0800, spike wrote:

> Keith I may be misunderstanding the process you propose.  I see no advantage
> in creating Pu239 by having the uranium atoms in solution, but I can imagine

There's one big advantage: removal of plutonium in a continuous process.
This is very different from periodically pulling rods, letting them decay
in a pool, saw them up in a hot cell and dissolve them in fuming nitric
acid, separating plutonium from uranium by Purex or similiar, and to casting
uranium back into a rod, to be irradiated. Iterate. Notice that you can't
ever beat continous process by an approximation of discrete steps as above,
unless you consider irradation of seconds, which is not viable because of
high process (above) friction.

This is another big advantage of liquid-core thorium reactor, with
continous separation of the ashes in a cycle. 

> couple of big disadvantages.  My understanding is for neutron capture by a
> uranium atom, the neutron must have a certain narrow range of momentum with
> respect to the uranium nucleus.  When the target uranium is in the solid
> form its momentum is zero, so the trick to facilitating neutron capture is
> in moderating the momentum of the neutrons.  Uranium in solution introduces
> an additional unknown: the momentum of the uranium atom.  

You might have a point there, but uranium salts in solution fission just fine.
Solutions are not gases, speed spread is very narrow there. The energy
spectrum distribution of moderated neutrons is not infinitely sharp either,
so it's a wash. (IIRC hotter cores tend to automatically downregulate
because of the capture mechanism you describe, not a problem in solution, though).
> Secondly, it appears to me one would greatly reduce the neutron capture
> probability by uranium atoms in solution because of the greatly reduced
> actual number of uranium atoms.

You will recapture most of the neutrons by the rest of the rods. They're
not wasted.
> So what is the advantage to having the U238 in solution?

Because you can continuously remove the fission products from the medium.
> If for whatever reason, this method really does produce more Pu239 (instead
> of way less which is what I would expect), seems like we could do the same
> trick even better with liquid U238, because of higher density of uranium
> nucleii.

It doesn't, because molten uranium won't absorb as many neutrons, and (the real reason)
you can reprocess molten uranium on the fly as trivially as with an ion
exchanger in a solution.

Eugen* Leitl <a href="http://leitl.org">leitl</a> http://leitl.org
ICBM: 48.07100, 11.36820            http://www.ativel.com
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