Uranium 233 is NOT the same as Uranium 235. That’s … sort of the whole point?
That said, they can both be used as nuclear fuels. They aren’t the same, as I said, so they have to be used and operated somewhat differently. Uranium 233 is significantly less ideal as a nuclear fuel for a lot of complex and various reasons, but some of the things that make it somewhat less ideal as a fuel also make it MUCH less ideal for (clandestine) nuclear weapons, so on the whole, even though it is sort of worse than u235 at BOTH things in some ways, the fact that it’s SO much worse at nuclear weapons makes it somewhat more attractive for power generation in exchange, and this is a good thing that makes it potentially worth using for power generation because nobody’s going to be able to secretly start a nuclear weapons program with it.
Note this is all pretty debatable, as there are, as far as I am aware, no actual examples of commercial U233 nuclear reactors in existence, and nobody has really had an opportunity to use it in a clandestine nuclear program, and this is all imaginary at this point. We are speculating about hypothetical performance here. We will not know what the real performance and viability is until somebody actually does it at scale within real constraints. For now, it’s strictly theoretical and that means it’s very much subject to debate and the real-world implementation may have nothing to do with any of these principles or projections. We just don’t know what a U233 power plant would actually be able to accomplish because there aren’t any. Some people claim it’s a superfuel. Maybe they’re right, I don’t know, but I believe that if it really was as great as its proponents say, somebody would’ve found a way to make it work commercially by now. They are invited to prove me wrong at any time. I’ll wait.
A nuclear reactor produces both energy and neutrons. With the right conditions, those neutrons can be used to produce new isotopes.
In a thorium reactor, 232Th absorbs a neutron to become 233Th. This has a 22 minute half life, decaying to 233Pa, which itself has a 27 day half life, decaying to 233U. 233U is fissile and can be used as fuel for the reactor.
235U is also fissile and can be used for fuel, but this is generally obtained by processing natural uranium to select the <1% of the material that’s 233U. This process is called enrichment.
Plutonium breeder reactors make 239Pu by irradiating 238U to capture a neutron. This undergoes a similar decay process as in the thorium fuel cycle: 239U -> 239Np -> 239Pu.
