The only reported incident has been from one of the European designed EPR reactors, which had a faulty fuel cladding that released some radioactive steam within the system.

Other than that, they've been pretty good. The main reason the reactors are safe is because we've designed them, especially with post-Fukushima improvements, to have a lot of passive safety built in by default.

Post-Fukushima improvements include, in addition to baseline passive nuclear safety, things like being able to take direct strikes from artillery without melting down. We've generally done a good job of over-engineering our reactors so that we can minimize any potential disasters.