There is still the problem of nuclear waste being highly radioactive for thousands of years and us not knowing how to deal with it properly.
What do you think we do with our current nuclear waste? What is "improper" about our current processes?
Is this a serious question?
We bury it underground in vast bunkers with hundreds of warnings and ominous-looking signs inteded to warn people thousands of years into the future not to fucking open the thing.
https://en.wikipedia.org/wiki/Onkalo_spent_nuclear_fuel_repo...
Of course we don't know how to handle it. We basically dump nuclear waste in glorified landfills. Look how great that turned out for our regular waste that doesn't pose the grave threat of biological/ecological hazard.
You talk as if that's obviously a bad idea but to me it seems peefe fly reasonable. Yes there is some concern about people thousands of years from now not understanding the warnings, but the people during right now and in the near future due to coal and climate change seem like a bigger concern at the moment.