But modern reactor designs could also use up 99% of fuel 'waste' until the waste products are either so unradioactive that they pose no danger or so quickly det

But modern reactor designs could also use up 99% of fuel 'waste' until the waste products are either so unradioactive that they pose no danger or so quickly deteriorate that even a simple metal drum could contain it for the necessary 100 years if it was somewhere dry. But since we don't have/use modern reactor designs and are sitting on 60 year old designs we don't have anywhere to use that 'waste' fuel yet.