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Not sure I'm following. Fission reactors split uranium into smaller atoms like barium and krypton. The remaining energy that comes out as afterglow heat in the

Not sure I'm following. Fission reactors split uranium into smaller atoms like barium and krypton. The remaining energy that comes out as afterglow heat in the repository is a small fraction of what already came out during fission. less than 1% remains an hour after fissioning.

nabla9 3y ago
You have the numbers reversed. In spent nuclear fuel 96% of the mass is the remaining uranium is still usable. Spend nuclear fuel (=LEU) used in these reactors have almost all potential energy left. You can use them if you close the nuclear fuel cycle with fast neutron reactors. The downside of it is that they FNR's are also good for making fuel for nuclear weapons.
- acidburnNSA 3y ago
  I don't have the numbers reversed. I'm talking about when a single atom actually undergoes fission, it releases 93% of its energy promptly as fission product kinetic energy, gamma rays, and neutron kinetic energy. An hour later, another 6% of the energy goes out as delayed betas and gammas. After that, only 1% remains to emerge as heat in the repository. What you're referring to is the fact that some reactors (aka breeder reactors, fast or thermal) can fission a much higher percentage of the total atoms loaded into the reactor, including most of the majority isotope (U-238) in addition to the minority (U-235). I wrote a bit about breeding and recycling here: https://whatisnuclear.com/recycling.html https://whatisnuclear.com/recycling.html
  - phkahler 3y ago
    >> don't have the numbers reversed. I'm talking about when a single atom actually undergoes fission... Well then maybe you should talk about the problem at hand, which is the stuff people are considering "nuclear waste" and wanting to bury.
- pfdietz 3y ago
  That 96% of the mass is 238U. It's usable in breeder reactors. It's not useful for today's burner reactors. We have far too much 238U for those already; enrichment is the process of stripping out 238U from natural uranium. It would be utterly pointless to recover more 238U for them. We already have great stockpiles of depleted U sitting around. The stuff is not worth very much right now. Reprocessing can recover some plutonium, which can be reused (once more) in MOX fuel. Spent MOX fuel cannot be reprocessed further for use in today's thermal reactors, though.
  - flangola7 3y ago
    Since it if just sitting around can I buy some? I would be happy to have a kilogram cube of DU
    - ben_w 3y ago
      Yes. Legality might depend which country you live in, and the stores I've seen sell only tiny quantities for high prices because they can (only collectors really want it and they will pay), but you can totally just buy some.

nabla9 3y ago

You have the numbers reversed. In spent nuclear fuel 96% of the mass is the remaining uranium is still usable. Spend nuclear fuel (=LEU) used in these reactors have almost all potential energy left. You can use them if you close the nuclear fuel cycle with fast neutron reactors. The downside of it is that they FNR's are also good for making fuel for nuclear weapons.

acidburnNSA 3y ago
I don't have the numbers reversed. I'm talking about when a single atom actually undergoes fission, it releases 93% of its energy promptly as fission product kinetic energy, gamma rays, and neutron kinetic energy. An hour later, another 6% of the energy goes out as delayed betas and gammas. After that, only 1% remains to emerge as heat in the repository. What you're referring to is the fact that some reactors (aka breeder reactors, fast or thermal) can fission a much higher percentage of the total atoms loaded into the reactor, including most of the majority isotope (U-238) in addition to the minority (U-235). I wrote a bit about breeding and recycling here: https://whatisnuclear.com/recycling.html https://whatisnuclear.com/recycling.html
- phkahler 3y ago
  >> don't have the numbers reversed. I'm talking about when a single atom actually undergoes fission... Well then maybe you should talk about the problem at hand, which is the stuff people are considering "nuclear waste" and wanting to bury.
pfdietz 3y ago
That 96% of the mass is 238U. It's usable in breeder reactors. It's not useful for today's burner reactors. We have far too much 238U for those already; enrichment is the process of stripping out 238U from natural uranium. It would be utterly pointless to recover more 238U for them. We already have great stockpiles of depleted U sitting around. The stuff is not worth very much right now. Reprocessing can recover some plutonium, which can be reused (once more) in MOX fuel. Spent MOX fuel cannot be reprocessed further for use in today's thermal reactors, though.
- flangola7 3y ago
  Since it if just sitting around can I buy some? I would be happy to have a kilogram cube of DU
  - ben_w 3y ago
    Yes. Legality might depend which country you live in, and the stores I've seen sell only tiny quantities for high prices because they can (only collectors really want it and they will pay), but you can totally just buy some.