Three Mile Island Accident

It began on March 28, 1979. A combination of stuck valves, human error in reading the gauges, and poor decisions led to a partial meltdown of the reactor core in Unit 2 at Three Mile Island nuclear power plant, located on the Susquehanna River in Dauphin County, PA. A hidden indicator light led an operator to manually override the automatic emergency cooling system for the reactor because he mistakenly believed there was too much coolant water in the reactor – the opposite proved to be true.

Radioactive gases were released into the atmosphere, and while they had minimal health effects according to the Nuclear Regulatory Commission, Governor Dick Thornburgh advised the evacuation of pregnant women and school-age children within five miles of the plant, which was later expanded to 20 miles. Within days, more than 140,000 people had left the area.

Massive demonstrations followed, including a rally in New York City that attracted nearly 200,000 people. Public fear of a repeat incident led to the immediate shutdown of several plants, and led to a moratorium on licensing and construction of all new reactors. Following the event, the number of new reactors in the United States declined every year from 1980 to 1998. And while the accident did not kill the nuclear industry, it did halt its growth. The Chernobyl disaster in 1986 and the Fukoshima accident in 2011 added to the industry’s decline.

The clean-up of Unit 2 at Three Mile Island began in August of 1979 and was finished in December of 1993, with a total cost of $1 billion. The unit was too badly damaged to be used, so it was gradually deactivated and permanently closed. Unit 1 had its license suspended temporarily following the accident, but was allowed to resume operations in 1985, under new ownership. The current license for Unit 1 will expire on April 19, 2034.

To see a video about the Three Mile Island incident from The New York Times, click here.