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Originally Posted by Digix
enrichment is quite trivial to do, all you need is lots of elecricity, i think best is magnetic ion, or gell separation, centrifuges take too much space, and produce poor and unpredictable results.
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For uranium, you need to use isotope enrichment. No matter what scheme you use, it takes a lot of space (think of a small city). Magnetic isotope separation also takes
a lot of power.
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magnetic separator can easily make almost completely pure isotopes no matter what initial mixture was. this will not work with uranium, ulness you have personal power plant to power that magnetic separator.
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It is a problem with plutonium too.
If you have a reactor designed for the purpose you can chemically separate the plutonium. That still is a major operation, but no isotope separation required, though you will be stuck with the implosion design.
If you have plutonium that has been sitting in a reactor for a long time, you have a problem. You want 239Pu, but there will be a lot of 240Pu, which has a high spontaneous fission rate. That means it is hard to get a good explosion out of it, because you can't keep the plutonium together for long - it will tend to predetonate. This is also why even conventional plutonium bombs require an implosion design (a pure 239Pu bomb could probably be built with a gun design).
Both 238Pu and 240Pu are bad. They are
hot, literally. That means you need an active cooling system for the bomb.
Note that the stuff you want is in the middle, and it is only one
AMU away from 238Pu or 240Pu. That makes it much harder to separate than 235U from 238U (three AMUs apart). Also, this is mass based, if you are trying to exclude 240Pu, you will concentrate 238Pu along with 239Pu. 238Pu will be concentrated
better than 239Pu because of the lower mass.
Along with that, there is no "nice" gas equivalent to uranium hexafloride, and this stuff is nasty (radioactively hot).
The U.S. considered a multibillion dollar program for plutonium enrichment. Laser enrichment was a leading contender (which would require a lot of R&D). They didn't go through with it because there wasn't sufficient need and they didn't want to develop the technology, opening the door to some other government sneaking away with the tricks.
I'm not aware of anybody doing large scale plutonium enrichment. It is just too hard. There are easier options, though they aren't easy options.