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March 28, 2019 - On March 28th, 1979, a partial meltdown of a nuclear reactor at a Pennsylvania power station caused a radiation leak that remains America’s most serious nuclear incident to date.
The Three Mile Island accident was the partial meltdown of reactor number 2 of Three Mile Island Nuclear Generating Station in Dauphin County, Pennsylvania and subsequent radiation leak that occurred on March 28, 1979. It was the most significant accident in U.S. nuclear power plant history and rates a five on the seven-point International Nuclear Event Scale: Accident with wider consequences.
It began with failures in the non-nuclear secondary system, followed by a stuck-open pilot-operated relief valve in the primary system, which allowed large amounts of nuclear reactor coolant to escape. The mechanical failures were compounded by the failure of plant operators to recognise the situation as a loss-of-coolant accident due to inadequate training and human factors, such as ambiguous control room indicators in the power plant’s user interface.
The accident crystallised anti-nuclear safety concerns among activists and the general public, and resulted in new regulations for the nuclear industry.
People expressed worries about regional health effects from the accident, but studies of the rate of cancer in and around the area since the accident determined there was a statistically non-significant increase in the rate and thus no causal connection linking the accident with these cancers has been substantiated.
The bill for making the site safe was $1 billion, and took from 1979 to 1993.
The plant is due to close in September 2019, but cannot be decommissioned until 2040, when radiation levels have fallen sufficiently.
- Backgrounder on the Three Mile Island Accident (U.S.NRC)
- Nuclear plant accidents: Three Mile Island (Union of Concerned Scientists)
- Three Mile Island Accident (World Nuclear Association)
- Time running out to save Three Mile Island from early closure (StateImpact Pennsylvania)
- Mar 28, 2019: Nuclear power industry still hurting 40 years after Three Mile Island accident (NewsAhead)