the raw material was mined. Just put the waste back in the same hole.

yeah it seems really simple, but then, you have the realities:

lots of uranium mining is open pits. like this one in namibia - Image - that’s not going to keep stuff in one place.

transporting it, hell even getting the producers to agree to accepting it for storage - would be a political nightmare.

even in places where it was mined underground, you have water tables to worry about. it’s simply not that simple.