Physical Insights

An independent scientist’s observations on society, technology, energy, science and the environment. “Modern science has been a voyage into the unknown, with a lesson in humility waiting at every stop. Many passengers would rather have stayed home.” – Carl Sagan

Uranium-232, thorium… oh, and The Bulletin.

with 2 comments

Something of a question for the readers:

Why is uranium-232, produced via a (n,2n) reaction from U-233 in a thorium breeder reactor, viewed as such a uniquely favorable impediment to diversion of material for weapons proliferation? You would expect a breeder reactor operating on a U-238/Pu-239 fuel cycle to produce some Pu-238 directly via the same (n, 2n) reaction in Pu-239 – the cross sections are about the same for fast neutrons – and Pu-238 is certainly a strong impediment to nuclear weapons use of the plutonium, as much as is U-232.

Does the Th fuel cycle actually offer some real advantage over a U fuel cycle in this regard , where the U fuel cycle does not deliver?

I suppose that the lesson to take home is that the fuels and operating conditions in power plant reactors are uniquely unfavorable for the production of weaponisable fissile materials, irrespective of the exact fuel cycle used, uranium or plutonium.

Also, the Bulletin of the Atomic Scientists seems to get a little more tabloid-like with every issue, to me at least – what’s with that?

It almost seems like every major piece in the current edition is skeptical of, cautious about, pessimistic about, wary of, or simply all out opposed to new expansion of nuclear energy in the United States and the rest of the world.


Written by Luke Weston

October 5, 2008 at 1:39 am

Posted in Uncategorized

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2 Responses

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  1. U-232 follows the same decay chain as thorium, only it follows it much more quickly because it has skipped all the “slow” steps at the beginning. That decay chain contains two strong gamma-emitting decay steps–bismuth-212 and thallium-208. Those strong gamma decays make fabrication, testing, and basic survival of a nuclear weapon very doubtful.

    Pu-238 on the other hand decays to U-234, which has a very long half-life, and from there follows the standard uranium-238 decay chain, which doesn’t have the strong gamma-emitting isotopes. The basic weapons-deterrence feature of Pu-238 is simply spontaneous fission and the high heat generation of its fairly rapid decay.

    Kirk Sorensen

    October 5, 2008 at 3:34 am

  2. The BAS really raised my ire by raising their newsstand price to $!2 (!) an issue. I doubt I’ll ever buy a copy of it again.

    Although I haven’t been around long enough to really know, I think that the BAS is somewhat more accepting about nuclear power than they were a few decades ago. But they have a real talent for publishing articles written by people who make the greatest possible stink over highly unlikely or non-existent technical problems, and most of the writers are stuck in an arms control paradigm whose days are looooooooooong past, IMHO. I just wish we could return to the way it was back in the 50s, when it actually represented a diversity of opinion and was an important venue for the dissemination of new information.


    October 10, 2008 at 1:02 pm

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