Some comments on this work (which has been greatly aided by Mike Pop and Professor Zeyun Wu):
1. The Molten Uranium Breeder reactor (MUBR) is a mixed spectrum nuclear fission reactor concept which gets most of its energy by direct or indirect fission of the plentiful uranium isotope U-238 (indirect fission of U-238 occurs when U-238 absorbs a neutron and decays to Plutonium-239, which is fissile and easily split like U-235).
2. The concept has been studied by using U.S. government nuclear simulation programs called MCNP and SCALE which are universally accepted as standards for nuclear research.
3. Almost all commercial nuclear generation of electric power worldwide is with nuclear fission reactors dominated by thermal fission of the rare uranium isotope U-235 (one atom in 140 atoms of mined uranium is U-235, almost all of the rest is U-238) (Thermal fission is splitting of atoms caused by absorption of slow (low energy) neutrons). The percentage of fuel atoms split in these reactors is roughly equal to the percentage of U-235 in the reactor fuel). Most of these reactors require partial refueling at least once every two years with removal of some of the fuel as Used Nuclear Fuel (UNF) which is replaced with new fuel.
4. Because the MUBR creates new fissile atoms (PU-239 and PU-241 which can be split by slow neutrons the same way U-235 is) it can produce 10 times as much energy per ton of fuel as other reactors, the fuel lasts longer than the life of the reactor so it is never refueled, and no UNF is taken out of the reactor until the end of the reactor life.
5. While the MUBR can use some existing UNF as part of its fuel, the point of the design is lots more energy per ton of fuel so it uses vastly less fuel than other designs and therefore cannot use large amounts of UNF as fuel.
6. The paper discusses the advantages of the MUBR and the large amount of work required to change it from a reactor concept to an operating reactor.