> Surely written warnings, if some future society discovers them, they might be curious enough to have decrypted at least one of our present day languages/methods of communication.

The pyramids were known for their entire duration of their existence, and investigated and/or plundered regularly. But we lost all knowledge of hieroglyphs for a time period of almost two thousand years (until we found the rosetta stone).

And at the same time we were using Uranium to give glass a wonderfully green sheen. And it glowed in the dark, too! Awesome!

If there is an event cataclysmic enough to wipe out all knowledge of nuclear repositories, it will likely wipe out human civilization at large. We can't make really useful predictions how much knowledge will be kept, and at what pace it will be rediscovered.