Now...if you want to deal with high level waste permanently, bury it in a subduction zone on the ocean floor. This will make it completely inaccessible to humans, and will store it until it gets incinerated and dispersed safely in the Earth’s mantle.
I thought of that idea myself.
However I can’t imagine how expensive it would be to build a container able to withstand the pressure to get it to the bottom intact.
I think the salt mines are the best option. These salt formations have existed for over a billion years. The biggest worry for radwaste burial is water intrusion. Any fissure permitting water intrusion in salt formations are self sealing.