[extropy-chat] Space elevator numbers III

[Eugen Leitl]

On Fri, Feb 16, 2007 at 07:06:11PM -0800, spike wrote:

> Keith, I would probably have put in more but for the fact that youuuu have
> me distracted worrying about and calculating how plutonium could be made
> with stuff ordinary people or dippy little governments could get.  The

Ordinary people don't run nuclear reactors in their cellar. 
I would be very surprised dipply little governments run ever a single
nuclear reactor that isn't periodically inspected, and critical
parts of it sealed. You should try buying a few tons of metallic
thorium, or even a large batch of thorium oxide on the world 
market. I doubt it's that easy, but then, I've never tried.

> solubility of uranium nitrate of 66g/100cc was a surprise.  66 g of uranium,

Not for me. I've got a little ampoule of it stashed somewhere, from undergrad
chemistry days. Depleted uranium is a commodity, and even nondepleted stuff 
should be easy to get, very unlike HEU (but you didn't miss
http://www.nti.org/e_research/e3_special_nuctrafficking.html , did you? 
Very strange, I did a double-take when I read that little bit of news
which never made the first page of major newspapers, which it should). 
But that's not the issue.

> what's that about 3cc, in a bit over 100 cc solution, nuclei spread apart by
> only a factor of 30 something from the solid state, ug, plenty of neutron
> captures possible, resulting Pu easily electro-removed from solution.  

No, Pu lands in the ion exchanger (in fact, you have to make the columns 
small enough so that you won't get a little bit too uncomfortable, especially
with all the resin and water around as moderators). You eluate it, and 
just produce plutonium metal via the normal route. You can't electrorefine
Pu from aqueous solutions. Not that's it needed, it's just normal metallurgy,
and normal high-precision milling (in a positive-pressure suit, though).
 
> I calculated an energy balance taking into account the kinetic energy of the
> recoiling U nucleus after absorbing the neutron, but that didn't help.  I
> get less than half a percent of the energy of the neutron ends up in kinetic
> energy.

I don't know what the big deal about it supposed to be. I never did any
formal radiochemistry nor nuclear engineering, but from reading newspaper
alone it's clear nuclear reactions proceed just fine in aqueous solution,
in fact, frequently you'd get nasty surprises which kill people because 
you haven't factored the extra moderation in. In fact, it's a masively
bad idea to step up to a slightly subcritical assembly, because people
are mostly water.
 
> Now we need to control all neutron sources.

No, preparative element transmutations require a reactor. Nothing
has changed. I presume the proliferation people are watching thorium,
too. Just because you or me don't know something, it doesn't mean
it's not elementary to nuclear engineers or chemists.

-- 
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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