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They can extract a little bit more energy out of spent fuel using a process like DUPIC [1], but they don't extract the vast energy remaining in the U-238, and t

They can extract a little bit more energy out of spent fuel using a process like DUPIC [1], but they don't extract the vast energy remaining in the U-238, and they also do not transmute it into shorter-term waste like fast-neutron reactors do, so the total value is pretty low. There are lots of CANDUs outside of Canada though! [2] [1] https://dspace.mit.edu/bitstream/handle/1721.1/45495/42255431-MIT.pdf https://dspace.mit.edu/bitstream/handle/1721.1/45495/4225543... (thesis) [2] https://en.wikipedia.org/wiki/CANDU_reactor#Active_CANDU_reactors https://en.wikipedia.org/wiki/CANDU_reactor#Active_CANDU_rea...

Retric 2y ago
U-238 has almost zero economic value, and it’s definitely negative when part of spent fuel. It’s literally the waste product of uranium enrichment and mostly used in ammunition. CANDU avoids the need for enrichment which means throwing a lot less U-238 out at the beginning. However it’s all the other bits like maintenance keeping nuclear expensive right now, reactor grade enriched uranium is still cheap and plentiful (~0.9c/kWh in fuel rods) which is why CANDU reactors don’t take off in the first place.
- acidburnNSA 2y ago
  The whole magic of breeder reactors is that they can turn U238 into Plutonium 239 for energy
  - Retric 2y ago
    All reactors do that. Breeder reactors operating on spent fuel can only utilize the U238 that wasn’t discarded in the initial enrichment process. That’s what happened to the vast majority of U238 in natural uranium used to make fuel. Roughly speaking to make 100kg of 5% enriched uranium fuel you need to throw away 1,000kg of U238 + ~3kg of U235 as 1,003 kg of depleted uranium.
    - acidburnNSA 2y ago
      Breeder reactors are defined as ones that turn more u238 into pu than the u235 they consume. The breeding ratio is greater than one in that case. So the net fissile material increases during operation.
      - Retric 2y ago
        Which again sounds nice, but simply isn’t useful right now. Understanding why really comes down to following each step of the progression from natural uranium ore > natural uranium > etc. But basically U238 is really cheap, and nothing else in the process is.

Retric 2y ago

U-238 has almost zero economic value, and it’s definitely negative when part of spent fuel. It’s literally the waste product of uranium enrichment and mostly used in ammunition. CANDU avoids the need for enrichment which means throwing a lot less U-238 out at the beginning. However it’s all the other bits like maintenance keeping nuclear expensive right now, reactor grade enriched uranium is still cheap and plentiful (~0.9c/kWh in fuel rods) which is why CANDU reactors don’t take off in the first place.

acidburnNSA 2y ago
The whole magic of breeder reactors is that they can turn U238 into Plutonium 239 for energy
- Retric 2y ago
  All reactors do that. Breeder reactors operating on spent fuel can only utilize the U238 that wasn’t discarded in the initial enrichment process. That’s what happened to the vast majority of U238 in natural uranium used to make fuel. Roughly speaking to make 100kg of 5% enriched uranium fuel you need to throw away 1,000kg of U238 + ~3kg of U235 as 1,003 kg of depleted uranium.
  - acidburnNSA 2y ago
    Breeder reactors are defined as ones that turn more u238 into pu than the u235 they consume. The breeding ratio is greater than one in that case. So the net fissile material increases during operation.
    - Retric 2y ago
      Which again sounds nice, but simply isn’t useful right now. Understanding why really comes down to following each step of the progression from natural uranium ore > natural uranium > etc. But basically U238 is really cheap, and nothing else in the process is.