Three Mile Island accident

Three Mile Island accident
Name	Three Mile Island accident
Caption	Aerial view of Three Mile Island Nuclear Generating Station (TMI) in 1979.
Date	28 March 1979
Location	Susquehanna River, near Middletown, Pennsylvania, U.S.
Coordinates	40, 09, 12, N...
Outcome	INES Level 5 (accident with wider consequences)
Casualties	None direct

Three Mile Island accident. The Three Mile Island accident was a partial nuclear meltdown that occurred on March 28, 1979, at the Three Mile Island Nuclear Generating Station in Pennsylvania. It was the most significant accident in the history of the U.S. commercial nuclear power industry. The event profoundly influenced nuclear safety regulations, public perception of nuclear energy, and led to major changes in both plant operations and oversight by the Nuclear Regulatory Commission.

Background and plant description

The Three Mile Island Nuclear Generating Station is located on an island in the Susquehanna River near Middletown, Pennsylvania. The facility was operated by Metropolitan Edison Company (Met Ed), a subsidiary of General Public Utilities Corporation. The station housed two pressurized water reactor units: TMI-1, which began operation in 1974, and the newer TMI-2, which commenced commercial operation in December 1978. The reactor vendor was Babcock & Wilcox, a major manufacturer of nuclear steam supply systems. The plant's design and operational procedures were typical of the era, governed by regulations from the Atomic Energy Commission and its successor, the Nuclear Regulatory Commission.

Accident sequence

The accident began around 4:00 a.m. on March 28, 1979, in the TMI-2 unit. A combination of mechanical failures and human error led to a loss-of-coolant accident. A malfunction in the secondary system caused the main feedwater pumps to stop, which led to an automatic shutdown of the steam turbine. This triggered an automatic scram of the nuclear reactor. A pilot-operated relief valve in the primary system stuck open, but instrumentation in the control room incorrectly indicated it was closed. Operators, misinterpreting confusing and contradictory instrument readings, mistakenly reduced emergency coolant injection, allowing the reactor core to become partially uncovered. This resulted in severe fuel rod damage and a partial nuclear meltdown.

Immediate aftermath and crisis management

In the hours and days following the initial event, plant personnel, Metropolitan Edison Company, and state officials struggled to understand the severity of the situation. A significant concern was the potential for a hydrogen bubble that had formed inside the reactor vessel to explode, though this was later deemed not credible. Pennsylvania Governor Dick Thornburgh, advised by the Nuclear Regulatory Commission Chairman Joseph Hendrie, recommended a precautionary evacuation for pregnant women and preschool children within a five-mile radius. The crisis prompted intense national media coverage, led by networks like CBS News and anchored by figures like Walter Cronkite. The reactor was finally brought to a stable cold shutdown on April 2, 1979.

Health effects and environmental impact

Extensive studies by multiple agencies, including the Nuclear Regulatory Commission, the Environmental Protection Agency, and the Department of Health, Education, and Welfare, concluded that the actual radiation releases had negligible effects on the physical health of the plant workers or the public. The maximum estimated radiation dose to any individual off-site was well below regulatory limits. However, the psychological and economic impacts on the local community around Harrisburg were significant, stemming from evacuation stress and fear. Independent reviews, such as the Kemeny Commission Report, supported these findings regarding minimal physical health consequences.

Investigations, reports, and legal proceedings

The accident prompted several major investigations. President Jimmy Carter established the President's Commission on the Accident at Three Mile Island, commonly known as the Kemeny Commission after its chairman John G. Kemeny. Its report was highly critical of the Nuclear Regulatory Commission, the plant operator Metropolitan Edison Company, and the reactor manufacturer Babcock & Wilcox. Concurrently, the House Interior Committee held hearings. The Nuclear Regulatory Commission also conducted its own investigation. Numerous lawsuits were filed, culminating in a 1984 settlement where General Public Utilities Corporation paid $25 million to affected residents without admitting liability.

Long-term consequences and legacy

The Three Mile Island accident had a profound and lasting impact. It halted the growth of the U.S. nuclear industry for decades, with no new reactor orders placed after 1978 being completed. It led to sweeping reforms in operator training, Nuclear Regulatory Commission oversight, emergency planning, and reactor design, including the formation of the Institute of Nuclear Power Operations. The accident galvanized the anti-nuclear movement in the United States, influencing protests such as those at the Seabrook Station Nuclear Power Plant. The undamaged TMI-1 reactor resumed operation in 1985, while the cleanup of TMI-2 lasted until 1993 at a cost of about $1 billion. The event remains a pivotal case study in safety engineering, risk perception, and crisis communication.

Category:Nuclear accidents and incidents in the United States Category:1979 industrial disasters Category:History of Pennsylvania Category:Nuclear energy policy of the United States