So, nuclear reactors are very safe except of dangerous-tech-xA45b which we only know is deadly after one or two incidents?

Actually, yes.

1) Don't use crappy Soviet reactors like Chernobyl; this should be a no-brainer.

2) Don't locate a nuclear power plant in a place where it can be flooded easily.

Other than the crappy Chernobyl reactor, I don't know of any inherently dangerous reactor designs, especially in Western nations.

AFAIK most modern designs are fail-safe, e.g. with passive features like control rods suspended with electromagnets over the reactor - if activated (or if power fails) they simply fall in and kill the reaction.