I dunno, the area around Fukishima is apparently not as contaminated as feared and is larely habitable But you're right given the sheer number of nuclear facilities that would presumably go unattended following a societal collapse, it's pretty scary.

I also read somehting years ago in a Margaret Atwood novel that hadn't previously occurred to me. If we had to rebuild a technological society, we would have no way to do it since we've mined and pumped everything that's easily reached, and wouldn't have the materials or tools to start again.