> can only assume that it's because the spent waste is still "valuable" so it's worth keeping around in case someone figures out more and more efficient ways o

> can only assume that it's because the spent waste is still "valuable" so it's worth keeping around in case someone figures out more and more efficient ways of processing it to recover useful material from it. Putting it 5km in the ground makes is completely unrecoverable by anyone. You can turn the waste into energy indeed, there's a few plants doing that and there's been prototype plants before. The issue is that it does not make sense economically yet since radioactive materials are so cheap.