The waste from fast reactors is just the fission products. It's about 1% as much waste by volume as conventional reactors. Encased it in glass, and the overall mix will be back to the radioactivity of the original ore in a couple centuries.

The waste from conventional reactors is the fission products plus lots of U238, a fair amount of plutonium, some U235, and various transuranics. The transuranics and plutonium are the really long-lived radioactive waste.