I can imagine some sort of post-apocalyptic copper age religion where the religious brotherhood exist to guard the 'cursed caves', without understanding why. But everyone knows that people who enter the caves either die at the hands of the strangely deformed beasts who live there, or of a mysterious sickness sometime afterwards.

Yeah, I probably played too much D&D as a child :)

The argument that we need to do something about this waste beyond the timeframe of our civilisation is mind boggling to me. This is the only risk we seem to take this seriously - in no other arena can I recall people arguing about what something will look like in 10,000 years. What about war between America and China? >1% chance, massive potential for death and destruction. Who cares if some poor person digs into an old nuclear waste dump in 500 years compared to that?

We can leave this problem to the future. If they have regressed so far that they can't detect nuclear then they have bigger problems than radiation poisoning.

Threats to energy security are so much more of a threat than potentially maybe not being able to figure out how to reprocess spent fuel until it isn't a health hazard.

The nuclear symbol is widely recognized across the planet so the only reason this would be a problem is if every one of the cultures that understands the importance of it is killed off.