The drill is set to begin at the plant in Peach Bottom on Tuesday evening and last from three to six hours. It's part of new federal requirements that the operators of U.S. nuclear power plants be prepared to handle a radiation leak emergency caused by an armed attack by terrorists, airplane strike or other scenarios.
Until now, emergency preparedness exercises involved scenarios in which equipment failed. The U.S. Nuclear Regulatory Commission says it found that too often those scenarios were predictable.
The partial meltdown of a Three Mile Island reactor in 1979 is considered the worst commercial nuclear power plant accident in U.S. history.