Not really. Chernobyl was explicitly known to have a vulnerability at a very unusual operating point. Fukushima was repeatedly flooded and officials refused to make protections against modest natural disasters. Three Mile Island was a mechanical failure.

There aren't many examples where something that went wrong was thought to be impossible. Much more often it is scenarios that were known to be possible, but ignored for reasons of cost or politics.

Nuclear plants are hardened against virtually everything. Certainly there may be things people haven't managed to think of, but there are many, many more things that we have thought of and haven't dealt with. A plant may be able to survive a bomb, but not a bunker buster or a full out war.

We don't want to and often can't ensure safety in every event that is thought of, which is why fail-safer designs are so popular in research and press circles.

It's a bit of an unfair rap since other thermal plants blow up all the time, dams burst, and windmills fall over. Radation makes everything more dangerous and has a permanent impact on our planet, but the actual rate of accidents is tiny. We do need more fail-safe plants (Fukushima in particular was inexcusable) but the real problem facing nuclear right now is cost.