On March 28 , 1979 , equipment failures and operator error contributed to loss of coolant and a partial core meltdown at the Three Mile Island Nuclear Power Plant in Pennsylvania . The mechanical failures were compounded by the initial failure of plant operators to recognize the situation as a loss-of-coolant accident due to inadequate training and human factors , such as human-computer interaction design oversights relating to ambiguous control room indicators in the power plant 's user interface . In particular , a hidden indicator light led to an operator manually overriding the automatic emergency cooling system of the reactor because the operator mistakenly believed that there was too much coolant water present in the reactor and causing the steam pressure release . The scope and complexity of the accident became clear over the course of five days , as employees of Met Ed , Pennsylvania state officials , and members of the U.S. Nuclear Regulatory Commission ( NRC ) tried to understand the problem , communicate the situation to the press and local community , decide whether the accident required an emergency evacuation , and ultimately end the crisis . The NRC 's authorization of the release of 40,000 gallons of radioactive waste water directly in the Susquehanna River led to a loss of credibility with the press and community
Three Mile Island Nuclear Power Plant
Three Mile Island accident
Nuclear safety in the United States