Three Mile Island Meltdown: Nuclear Safety Crisis Ignites

A stuck valve and a series of human errors triggered America's worst nuclear accident. At 4:00 AM on March 28, 1979, a pressure relief valve on the Unit 2 reactor at the Three Mile Island nuclear power plant near Harrisburg, Pennsylvania, opened automatically during a routine malfunction and then failed to close. Coolant drained from the reactor core for more than two hours while operators, misreading their instruments, actually reduced emergency cooling water flow, believing the system had too much water rather than too little. The reactor's core began to overheat within minutes. Zirconium fuel rod cladding reacted with steam to produce hydrogen gas, which accumulated in the reactor building. By the time operators realized the valve was stuck open, roughly half the core had melted. Radioactive gases and contaminated water leaked into the containment building and, in smaller quantities, into the atmosphere. Pennsylvania Governor Richard Thornburgh ordered the evacuation of pregnant women and children within a five-mile radius. The crisis lasted five days. A hydrogen bubble formed inside the reactor vessel, raising fears of a catastrophic explosion. Nuclear Regulatory Commission officials gave conflicting information to the public and the press, creating panic that spread far beyond the evacuation zone. An estimated 140,000 residents fled the area voluntarily. President Carter, a former nuclear submarine officer, visited the plant on April 1 to calm public fears. No deaths or injuries were directly attributed to the accident, and the amount of radiation released was small. But Three Mile Island effectively killed the American nuclear industry for a generation. No new nuclear plant was ordered in the United States for over 30 years. The NRC implemented sweeping safety reforms, and the incident became a case study in how cascading equipment failures and poor operator training can combine to produce a disaster that no one designed for.