well depends on the nuclear powerplant. First off most western build nuclear reactors has a containment building. This the the reinforced concrete dome over the reactor, which is designed to contain a blast from inside and will also protect from outside dangers. Such a containment building, will prevent radiation particles from being being released in the air. Such a structure would have significanty reduced the impact of the chernobyl incident.

That and all the other safety meassures should make a nuke plant extremly safe. You shouldn't worry about that too much.

Meassure to be safe is checking the wind directions and move if something did wend wrong.