On March 28, 1979, the worst nuclear accident in United States history occurred in central Pennsylvania. The incident was rated 5/7 on an International Nuclear Event scale and led to a sharp increase in anti-nuclear sentiment throughout the nation.
Three Mile Island, the facility where the partial meltdown took place, is located near Middletown, Pennsylvania. A series of mechanical failures in the second reactor's cooling system led to the disaster.
At 4 a.m., the accident occurred. The reactor shut down without warning, causing a relief valve to open. It should have shut ten seconds later, but remained open; the instrumentation indicated otherwise, which misled the power plant's operators. Over the course of the next few days, radioactive gasses leaked from the plant to the surrounding areas. Luckily, the radioactive content of these gasses was not enough to cause radiation sickness in any inhabitants of the area.
There were no sicknesses or deaths as a result of the Three Mile Island incident, though the incident caused considerable panic in the area. Confusion in the media led to a minor evacuation. The second nuclear reactor, the core of which melted, was completely destroyed. Clean-up took twelve years and cost $973 million.
Though no one suffered injury or death as a result of the Three Mile Island accident, it led to a sharp increase in anti-nuclear sentiment in the country. The Pennsylvania Department of Health kept records on 30,000 people who lived within five miles of Three Mile Island until 1997, when it was determined that there were no long-term health effects from the incident.
This incident led to increased safety precautions in nuclear facilities and today is remembered as one of the most devastating events in Pennsylvania history.