6 ms·
> It's also very difficult to store because while an individual weapon may not be a critical mass, if you have tens or hundreds of weapons you have to worry abo
by implements 4y ago
> It's also very difficult to store because while an individual weapon may not be a critical mass, if you have tens or hundreds of weapons you have to worry about them getting close enough to worry about accidentally assembling a critical mass just from proximity, which, would of course, be bad.
Plutonium is an alpha emitter, and I believe the pits are plutonium alloyed with gallium and plated with gold to manage that and reduce chemical interactions with their immediate environment - there’s no “critical mass” storage problem, I think.
[https://en.wikipedia.org/wiki/Pit_(nuclear_weapon)#Material_considerations https://en.wikipedia.org/wiki/Pit_(nuclear_weapon)#Material_...]
- smaddox 4y agoPlutonium is definitely able to go critical: https://en.m.wikipedia.org/wiki/Demon_core https://en.m.wikipedia.org/wiki/Demon_core A plutonium sphere of roughly 10 kg is sufficient.
- SlickNixon 4y agoI believe the original question was whether storage of multiple weapons in the same vicinity could result in accidental assembly of a critical mass, which appears to be something the author of the original blog came up with on their own.
- ttyprintk 4y agoI think modern US designs are fusion boosted, making them immune to predetonation. Older experiments are increasingly dangerous, especially high-yield uranium guns.
- SlickNixon 4y agoFission, boosted, or fusion all start with a fission bomb with a possibility to fizzle.
- skorpeon87 4y agoA single bomb core is a sub-critical mass; needing either neutron reflectors or another source of neutrons to start a chain reaction. But if you pile a bunch of such cores up together like they were cannon balls, that inherent safety goes right out the window.
- ttyprintk 4y agoIn the context of this blog post, which explosive parts should we mothball and which ones are too dangerous to store intact, it’s unwise to store pre-boosted plutonium cores at all. But, as a thought experiment, what is the difference between a pile of boosted-era plutonium cores; and a weird but moderated reactor? Specifically, does an arbitrarily-sized pile of weapons-grade plutonium marbles have the same inevitability of criticality you expect than if those are designed for use in boosted triggers?
- rjsw 4y agoI thought there was a story of Richard Feynman going round Oak Ridge and realizing that they were getting close to a critical mass of stuff stored in adjacent rooms.
- SlickNixon 4y ago>Feynman had discovered that the Y-12 Plant was storing uranium nitrate solution enriched in U-235 in drums holding 300 to 3,000 gallons. After performing some calculations, the young physicist determined that the drums were placed in potentially unsafe arrangements in a number of buildings.[0] Looks like fluids again, not warheads. https://exploreoakridge.com/how-a-26-year-old-physicist-may-have-saved-oak-ridge-from-nuclear-disaster/ https://exploreoakridge.com/how-a-26-year-old-physicist-may-...
- kennend3 4y ago> there’s no “critical mass” storage problem, These accidental criticality accidents indicate otherwise: https://en.wikipedia.org/wiki/Criticality_accident https://en.wikipedia.org/wiki/Criticality_accident Accidentally going "critical" is a very real risk, especially with plutonium and it allotropes
- SlickNixon 4y agoAll of those examples involve reactors, single cores, or fluid containers.
- kennend3 4y agoyes.. it seems a few people misunderstood the statement as "plutonium cant go critical" vs the correct interpretation "storing pits close to one another".
- mikeyouse 4y agoThose are only the confirmed criticality incidents -- there have been "near misses" by just plain idiocy in storing plutonium, including a US nightmare where they decided to gather a bunch of rods together to take a picture of them all in frame. https://www.science.org/content/article/near-disaster-federal-nuclear-weapons-laboratory-takes-hidden-toll-america-s-arsenal https://www.science.org/content/article/near-disaster-federa...
- SlickNixon 4y agoI think the main source of confusion is here is that the original author said "weapons", which about half of commentators have taken to mean weapons/warheads and half have taken to mean nuclear material of any variety.
- mikeyouse 4y agoYeah that's a fair point -- it's unlikely for pits to ever achieve accidental criticality given their design and setting. Much less so for plutonium in general which you'd likely have to deal with anywhere you have a bunch of warheads hanging out.
- skorpeon87 4y agoPu-239 is an alpha emitter, but that's not the end of the story. All plutonium weapon cores are also neutron emitters because all weapons grade plutonium is impure and contains 2-7% Pu-240. Pu-240 is very prone to undergoing spontaneous fission which emits neutrons. So the presence of neutron radiation around a plutonium weapon core is unavoidable. Furthermore, when Pu-239 is struck by neutrons (from the Pu-240 contaminant, for instance), it has a chance of undergoing fission and that results in the release of more neutrons which can cause additional Pu-239 to undergo fission. This chain reaction is how Pu-239 bombs work. A properly stored core will not sustain this chain reaction because the core is in a sub-critical configuration. So there is in fact a very serious critical mass concern with plutonium bomb cores.
- not2b 4y agoYes, alpha particles aren't relevant to the fission reaction, so the fact that it's easy to shield against alpha emission isn't relevant. It's all about the neutrons.
- not2b 4y agoThe alpha particles don't cause the chain reaction. Neutrons do, and they are a good deal harder to shield than alpha particles. The rate of spontaneous fission is very low but once it gets started, in a critical mass it will keep growing.