because people just naturally have an "if one, then all" mentality. all muslims hate america and are out to kill us. everyone in the soviet union supported communism. one guy puts a bomb in his shoe, everyone is going to board an airplane with a bomb in their shoe. all guys play CoD. all americans are stupid. all nuclear plants are now dangerous.
now are any of the above true? no, not at all, but people generalize for convenience's sake. why bother making a situation more complex for yourself when you can just generalize? it's much easier to assume that all muslims are terrorists and to simply shun them than to understand that they are not tied to the small group of extremists that are deemed a threat to homeland security, and furthermore that extremists exist in nearly every religion or society. (spanish inquisition, anyone?)
so first, when we think of a reactor meltdown, we think of chernobyl. we don't really think of the actual circumstances under which the situation occurred (no core containment and numerous regulations being broken), we just know that reactor meltdown = massive area uninhabitable and lots of deaths to radiation sickness. we don't think of Three Mile Island, which would be a more comparable situation due to that reactor being contained and very similar to the design of the reactors used in Japan. obviously no reactor meltdown is by any means safe, but it's not the nuclear armogeddon that we treat it to be.
second, let's look at what people are really concerned about, which is the large number of nuclear facilities in eastern america. now, let's think of what could damage them. no weather could hurt it. if you think that a nuclear facility isn't built to handle a tornado or a category 5 hurricane, you must also think that the employees play hot potato with the fuel rods in their spare time. the only thing that could potentially damage them weather-wise would be an earthquake. the east is far far away from even a fault line, let alone any tectonic rifts. japan was seated right on two tectonic plates. the chances of an earthquake in east america is infinitely smaller than it is in Japan. The most powerful earthquake here in the east has been little over a 1 on the richter scale. almost all buildings are designed to handle much higher numbers on the richter scale, and nuclear reactors are sure to be able to handle up to at least an 8 (as japan's were). considering that there are no large quakes in the east ever on record, there is no reason to believe that one could come (i could even prove that to you mathematically). also, let's stop to think that even though the power of this quake was so great that not even the plant was capable of standing up to it, they STILL managed to bring it under control.
the only thing non-weather related we have to worry about is an attack. but from who? you can't just drop a bomb on one, you don't honestly think that they weren't preparing for bombings when these facilities were built back during the Cold War. You'd have to do it from the inside. and good luck with that, whoever tries it.
basically, i'm not worried. there is no reason to be. i can't start panicking about improbable things. because then i'd have to start worrying about alien invasions and zombie outbreaks. not that i haven't thought about what i'd do in the latter.