Here's the authoritative summary of the capabilities of transmutation and partitioning [1]. Thorium reactors do indeed produce fewer transuranics, since Thoriu

Here's the authoritative summary of the capabilities of transmutation and partitioning [1]. Thorium reactors do indeed produce fewer transuranics, since Thorium-232 is 6 AMUs lower down the chain than Uranium-238. Used nuclear fuel is generally 95% U-238, 1% Pu and minor actinides, and 4% fission products. If you do chemical separation to partition the transuranics you can then try to burn them in a variety of reactors. In slow-neutron reactors using Thorium or Uranium fuel, they'll burn ok if they're well partitioned. In fast-neutron reactors, you can burn them with out as aggressive of partitioning. So it's probably easier and cheaper to reprocess UNF for fast reactors. They're far less sensitive to neutron-poisons and fertile species (e.g. fission products and U-238). Any breeder reactor will make 2 orders of magnitude less TOTAL waste than a non-breeder. Thorium can breed with slow neutrons (which requires continuous removal of the neutron poisons via online chemistry, usually requiring fluid fuel). Uranium can breed with fast neutrons in solid fuel or in fluid fuel. Note I say total waste, not high level waste. High-level waste is proportional only to the burnup (fraction of the fuel you put in that gets fissioned) and doesn't include any process waste from before that (e.g. enrichment or reprocessing waste like U-238). In a fast neutron uranium-fueled reactor, you can transmute the hell out of all actinides, leading to waste that decays to low levels in a few hundred years. See the link below. Thorium's only true physical advantage is that it alone allows breeding with slow neutrons, which can be done with low fissile densities. Other than that, Uranium and Thorium have pretty similar characteristics and capabilities in advanced reactors. [1] https://www.iaea.org/publications/7112/implications-of-partitioning-and-transmutation-in-radioactive-waste-management https://www.iaea.org/publications/7112/implications-of-parti...