I've always thought the Nuclear Power plant meltdown event was stupid. There isn't a gas line explosion event, a coal mine explosion event, a dam failure event, or any number of other things that could damage/destroy a city. Right now the worst event we have is the tsunami and all that does is destroy a couple easily replaceable buildings. Really disastrous tsunamis, earthquakes, tornadoes, etc. will wipe a city off the face of a map, but we don't have events that do that because they wouldn't enhance the gameplay, just encourage save-scumming. I think it makes much more sense to be able to build an ordinance building or National Wonder (something like the NRC) that increases maintenance costs of nuclear plants but eliminates the risk of meltdown.