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Comment by CWuestefeld | Hacker News Reader

From the OP:

You will hear that we can’t make bombs out of U-233 because it is a virulent gamma-ray emitter. This is not true, and I find it curious that it is used as a reason. U-233 has a 158,000-year half-life. What they are referring to is the protactinium-233 contaminant, which has a 27-day half-life, beta-decaying into U-233 with gamma-ray involvement. Chemically scrub the protactinium, of course, or just wait a year and it will be gone.

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No, that's wrong. The claim is that the bred U-233 will be contaminated with U-232, which is very hard to get rid of, and has the hard gamma emitter Thallium-208 in its decay chain.

Where would the U-232 contamination come from, if it's bred U-233? Does thorium also just sometimes decay into the lighter isotope?

Sometimes the thorium, when it absorbs a neutron, will emit two neutrons and turn into thorium-231, which decays (though a couple more isotopes) into U-232. It can also be formed when U-233 absorbs a neutron and emits two, forming U-232.

How hard this would be to separate depends on the type of LFTR design you're using. However, you could also include some thorium-230 in the fuel mix to denature any protactinium produced, so there's really no way around having U-232 mixed with the bred U-233. Here's a blog post with more details on the entire process:

http://energyfromthorium.com/2006/10/06/denaturing-thorium-w...

What about this?

http://www.technologyreview.com/blog/arxiv/25855/?ref=rss

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