A chemistry teacher I had (who was an advisor to the military on nuclear subjects and taught nuclear weapons classes for the military before he became a professor) taught us that uranium can be converted into plutonium. Its not so much that the uranium becomes plutonium that is important (I already knew that) it was that he said that the 99.3% of non-fissionable uranium-238 could become fissionable plutonium-239 by bombarding it with things like beta and alpha particles. I forget which though. The point is that natural uranium is 99.3% U-238 and 0.7% is U-235, and the U-235 is the fissionable type.
If this is true and you can convert U-238 into P-239 why don’t more countries have nuclear weaopns? I thought U-238 was really easy to get, it was just U-235 that was hard to find. So if the 99.3% of U-238 that makes up natural uranium can be converted into plutonium-239 why isn’t it done more often, why do I always hear about uranium enrichment (which involved 0.7% of uranium) instead of converting uranium into plutonium (which, I assume, can be done with 99.3% of uranium) when nuclear weapons are discussed?
It’s true that getting a U-238 atom to absorb a neutron can turn it into Pu-239 (after a short hop through Neptunium-ville), but Pu-239 is itself subject to fission, so if you let your reactor run long enough, the Pu-239 will mostly be consumed through fission (from high-speed neutrons) or conversion into Pu-240 (through absorption of low-speed neutrons). Pu-240, it turns out, is not nearly as useful as an explosive, and it has a nasty tendency to spontaneously fall apart, spraying neutrons all over the place and thus making it extremely hazardous to nuclear technicians. A special-purpose reactor is required to produce Plutonium with a less than 7% concentration of Pu-240 (i.e. “weapons-grade”). A conventional commercial reactor lacks the necessary machinery to do this (since it would involve a constant-stop-and-start, and delicately extracting the Pu-239 before it can fission or covert to Pu-240). Building a special-purpose reactor offers no economic benefit (since it can’t be used to generate steady electricity) and it’s damn hazardous, so without a full-blown arms-race in effect, no nation is likely to build such reactors when Uranium bombs are relatively simple and inexpensive.
Commerical reactors can and do produce Plutonium with high porportions of Pu-240 (i.e. “reactor grade”) which can be used as a fuel source but is impractical as a bomb source.
You can indeed convert uranium 238 into weapons grade plutonium by bombarding it with the right particles, but the required particles are neutrons, not alpha or beta.
That makes the conversion a difficult prospect because the only way to get a decent volume of neutrons is with a nuclear fission reactor. Reactors are technically tricky to handle. Since uranium reactor fuel is mostly the non-fissile uranium 238 anyway, you can run a reactor so a proportion of the fuel is converted into plutonium 239 and plutonium 240.
Your second problem is, it takes a pretty zippy neutron to convert an atom of uranium 238 into an atom of plutonium 239. Whereas you need slow neutrons to sustain the fission reaction in the reactor itself, and slow neutrons create plutonium 240, which is too fissile for weapons applications. So you have to tweak the reactor so it runs with just enough slow neutrons to keep itself going, but enough fast neutrons to keep the plutonium 239 /plutonium 240 ratio acceptably high for weapons use. This is also technically tricky.
Your third problem is, once you have plutonium 239 in your reactor, it can function as a fuel and so you have to arrange your reactor so that it produces plutonium faster than it consumes it, although that isn’t actually very hard.
Your fourth problem is, what you are left with is are fuel rods containing a radioactive mixture of uranium, plutonium, and all the little by-product isotopes that are radioactive as hell. At this stage they are really hard to handle - they heat up on their own and they put enough radioactivity to pose a major hazard. You have to park your spent fuel rods in a cooling pool for about a year while all the shorter-lived isotopes decay away, leaving the rods slightly more handleable, and then you can get on with the business of extracting the plutonium.
Your fifth problem is, manufacturing a plutonium bomb is technically challenging compared with a uranium bomb, which quite frankly a decent Junkyard Wars team could do, given the weapons grade uranium.
Converting Uranium into Plutonium merely by bombarding it with neutrons does not seem physically possible. Uranium is element 92, Plutonium is number 94, which means that Pu-239 has two more PROTONS than U-238, and one LESS neutron.
beta particle emissions convert neutrons into protons. A Uranium atom with 147 neutrons is too unstable so neutrons get converted to protons and eventually you convert Uranium with 92 protons and 147 neutrons into something that has 94 protons and 145 neutrons, aka Plutonium-239.
