> Why do you think we don't know how to deal with it properly?

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.