Your assumption is that every country is guaranteed to have access to underground places that are "geologically stable" over the required time-period, aren't aquifers, or at risk letting water in by some other means.
The assumption is simply wrong.
The assumption is simply wrong.
I mean a whole lot of coal plants do pump uranium dust into the air. If you did it with the nuclear waste you'd pump worse isotopes into the air, but the volume would be tiny.