Nextbigfuture has had many articles that try to educate people that what we call nuclear waste is unused fuel for different nuclear reactors. The waste is fuel that is mostly even numbered isotopes.
Unused fuel (aka nuclear waste) can be used as fuel in fast reactors like old fast reactors and molten salt nuclear reactors. Molten salt reactors are being developed in China and many by US companies.
Uranium 238 can be fissioned in any nuclear reactor that generates fast neutrons.
About 20 fast neutron reactors (FNR) have already been operating, some since the 1950s, and some supplying electricity commercially. Over 400 reactor-years of operating experience has been accumulated. Fast reactors more deliberately use the uranium-238 as well as the fissile U-235 isotope used in most reactors. If they are designed to produce more plutonium than the uranium and plutonium they consume, they are called fast breeder reactors (FBRs). But many designs are net consumers of fissile material including plutonium.* Fast neutron reactors also can burn long-lived actinides which are recovered from used fuel out of ordinary reactors.
Uranium 235 is naturally fissile. Easily fissioned with low energy neutrons.
Uranium-235 fissions with low-energy thermal neutrons because the binding energy resulting from the absorption of a neutron is greater than the critical energy required for fission; therefore uranium-235 is a fissile material. Uranium-238 is a fissionable material but not a fissile material.
A fast neutron is a free neutron with a kinetic energy level close to 1 MeV (100 TJ/kg), hence a speed of 14,000 km/s, or higher. They are named fast neutrons to distinguish them from lower-energy thermal neutrons, and high-energy neutrons produced in cosmic showers or accelerators.