UPower is a fast reactor. 99% of nuclear waste, and almost all long-term waste, is transuranics, which fast reactors use as fuel. What remains is the fission products, which go back to the radioactivity of the original ore in a couple centuries. Encase them in glass and bury them, and you're good.

Helion is a fusion reactor. Its "waste" is helium, and it uses a reaction that produces only 6% of its energy as neutron radiation.

In both cases the reactor itself may become somewhat radioactive, but that's another short-term problem.