The Three Mile Island accident was the worst nuclear power plant accident in US history. It occurred on March 28, 1979, at the Three Mile Island Nuclear Generating Station in Pennsylvania. A series of equipment malfunctions and human errors led to a partial meltdown of the reactor core in Unit 2 of the plant. Radioactive material was released into the environment, but there were no fatalities or acute health effects among the general public. The accident resulted in significant changes in the way nuclear power plants are designed, operated, and regulated in the United States.