Read about burner mode of breeder reactors, they allow to "burn" spent nuclear fuel and make the resulting waste much safer in the long-term, i.e. not only volume of waste will be 100 times smaller, but also the "burnt" fuel will be relatively safe radiologically speaking after just several hundreds years, instead of tens of thousands of years for waste from existing reactors).

https://en.wikipedia.org/wiki/Breeder_reactor#Waste_reductio...