Chernobyl, Fukushima, and a long list of smaller accidents: https://en.m.wikipedia.org/wiki/Nuclear_and_radiation_accide...

I'm not sure Fukushima was at all problematic. Most People are confused as hell because there was massive tsunami damage and it all got subconsciously jumbled together.

It was rated a 7 (major accident) by the IAEA. The only other incident with that rating was Chernobyl.