Stubsack: weekly thread for sneers not worth an entire post, week ending 2nd November 2025


Als Antwort auf Charlie Stross

every batch of plutonium is made mostly out of Pu-239 that's just how plutonium works. it can't be separated into isotopes in any meaningful amounts so any batch of plutonium is also a mix of a couple of isotopes. reactor grade might be something like 55% Pu-239 plus say 12% also fissile Pu-241 with the rest being nonfissile Pu-240, Pu-242 and Pu-238 in that order. the newer reactor and fuel pin design, the higher burnup and the less fissile isotopes will be present at the end of the cycle. even in purely uranium fueled reactor about third of energy at the end of the fuel cycle comes from plutonium bred in the same fuel pin. i can elaborate on that if you want to
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Als Antwort auf fullsquare

AIUI for optimal nuclear weapons (ie. lightweight pits that maximize fission) you need to be very careful about which phase of metallic plutonium you use (it has dozens). IIRC an alloy with about 2% germanium in delta-phase is densest: make it with as close to 100% Pu-239 as you can get. (This was declassified in the 1970s.) You're also going to need some tritium gas to fill the hollow core, and other exotica (never mind the carefully timed explosive lenses to drive the implosion).