Three Mile Island Accident
A partial meltdown at Three Mile Island nuclear plant caused the worst US nuclear accident
March 28, 1979
America's Worst Nuclear Accident
On March 28, 1979, a cooling system malfunction at the Three Mile Island Nuclear Generating Station near Harrisburg, Pennsylvania caused the partial meltdown of reactor number two. A series of mechanical failures and operator errors allowed the reactor's core to overheat. Radioactive gases were released into the atmosphere, and the possibility of a major explosion kept nearby residents in fear for several days. Pennsylvania's governor recommended that pregnant women and young children within five miles of the plant evacuate.
What Actually Happened
Roughly half the reactor core melted during the accident, but the containment building — designed to prevent radioactive material from escaping — held. The amount of radiation released into the environment was relatively small, and no direct deaths were caused by the accident itself. However, the accident shook public confidence in nuclear power across the United States and the world. Thousands of residents evacuated voluntarily, some never returning. The cleanup of the damaged reactor took over a decade and cost nearly one billion dollars.
The Impact on Nuclear Energy
Three Mile Island had a profound and lasting effect on U.S. nuclear policy. No new nuclear power plants were ordered in the United States after 1978, and many planned plants were cancelled. Safety regulations were significantly tightened. The accident came just twelve days after the release of the film "The China Syndrome," which depicted a fictional nuclear accident, adding to public alarm. Debates about the long-term health effects on nearby residents continue. The incident remains a pivotal moment in energy history, shaping nuclear policy for decades. Use our date calculator to see how long ago it occurred.