The Three Mile Island accident was a partial nuclear meltdown which occurred in one of the two United States Three Mile Island nuclear reactors in Dauphin County, Pennsylvania, on March 28, 1979. It was the worst accident in U.S. commercial nuclear power plant history. The partial meltdown resulted in the release of small amounts of radioactive gases and radioactive iodine into the environment, due to the release being small, the accident has not been linked to a single cancer fatality.[2][3][4][5]