Anniversary of the Three Mile Island Incident

Three Mile Island

On March 28, 1979, a partial nuclear meltdown occurred at the Three Mile Island Unit 2 (TMI-2) reactor, near Harrisburg, Pennsylvania. It was the most serious accident in U.S. commercial nuclear power plant history, and was given a rating of 5 out of 7 on the International Nuclear Event Scale.

The accident began around 4:00 a.m. due to equipment failure and operator error. A valve failed to shut properly, coolant leaked, and the reactor overheated. The Nuclear Regulatory Commission (NRC) authorized the release of thousands of gallons of radioactive waste water into the Susquehanna Rive, and more than 100,000 people were evacuated from the area. The accident was soon contained, and no deaths have ever been attributed to the incident.

“A combination of personnel error, design deficiencies, and component failures caused the Three Mile Island accident, which permanently changed both the nuclear industry and the NRC. Public fear and distrust increased, NRC’s regulations and oversight became broader and more robust, and management of the plants was scrutinized more carefully. Careful analysis of the accident’s events identified problems and led to permanent and sweeping changes in how NRC regulates its licensees – which, in turn, has reduced the risk to public health and safety.”

The HSDL has several documents and resources for you to read relating to this serious accident, as well as information on lessons learned and nuclear safety today. Some of these documents can be found below:

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