It's not as big of a problem as you're thinking. "Waste" can be used in breeder reactors to generate energy. This burns up >90% of the material. The remainder decays relatively quickly, not over geological time scales. Volume wise it's really not much. The entire nuclear industry so far has produced less than a 100kT of waste, a cube with a side length of about 30 meters. This is before putting the stuff in a breeder reactor.