12. Three Mile Island: Ignored Indicator Light
On March 28, 1979, the Three Mile Island nuclear power plant experienced a partial meltdown due to a combination of equipment malfunctions and operator errors. A critical issue was the pilot-operated relief valve (PORV) failing to close, leading to a loss of coolant. Operators misinterpreted the control room indicator light, which signaled that the valve was closed, when in fact it remained open. This misunderstanding prevented timely corrective actions, exacerbating the crisis. For more details, refer to the Nuclear Regulatory Commission’s backgrounder on the Three Mile Island accident. (nrc.gov)
