All… three of them if you really try hard? Really only two qualify as disasters to me. Three Mile Island wasn’t great, but certainly not a disaster on any level I can figure.

Yeah Chernobyl was the only really bad one. Windscale was bad also but that was a long time ago and not a power reactor. Neither reactor design is anything anyone would try to run today.

Edit: Well, RBMKs are still running in Russia but with significant safety upgrades.