The idea that civilisation collapses and then recovers to the specific extent, where it is advanced enough to have coal-mines or similar, but not to know about radiation. Then it must find this particular repository and start digging, and die. Thousands of years must pass but they must dig up this sight withing a particular 100-year period of their development.

This is such a stupidly contrives scenario that you might as well plan for an alien incasion or zombie apocalypse. Lime prerequisite for that theory is civilisation collapsing, our investment in making sirebcovilisation does not xollapse is zero. You deal with it by making sure civilisation does not collapse.