The half life of fall-out from the Hiroshima and Nagasaki bombs was a couple of decades.
The half life of nuclear waste from powerplants is anywhere from thousands of years to millions of years, depending on the mix of isotopes.
anywhere from thousands of years to millions of years
only in a strictly thermal reactor environment, if you’re using a fast reactor, something like the SSR that is currently being worked on in canada, it can both burn waste, and reduce it’s lifespan to a much more reasonable length.
As always, development is the problem, if we had more energy being focused on this, we would be farther along, but such is scientific development.