The Three Mile Island accident occurred on March 28, 1979, at a nuclear power plant near Harrisburg, Pennsylvania. It was the most serious accident in U.S. commercial nuclear power plant history, involving a partial meltdown of one of the reactors. The incident was caused by a combination of equipment malfunctions, design-related problems, and operator errors. Despite the severity of the situation, the accident resulted in minimal radiation release, and no immediate injuries or deaths were reported. The event led to widespread public concern about nuclear safety and prompted significant changes in regulations and oversight for the nuclear energy industry in the United States.