@frank
Pu239 is a fissionable fuel and is often used in nuclear power plants today, this makes good sense as more energy is produced for each tonne of uranium dug out of the ground. The drawback is that the spent fuel needs to be reprocessed to extract the Pu239, reprocessing spent nuclear fuel is difficult and dangerous.
That may remove the problem of Pu239 but it still leaves plenty of other isotopes with very long half-lives, the technologies available to burn these up are generally in their infancy and problematic.