Three Mile Island Nuclear Generating Station

Three Mile Island Nuclear Generating Station. It was a major nuclear power facility located on an island in the Susquehanna River near Harrisburg, Pennsylvania. The station is most widely known for the partial core meltdown in its Unit 2 reactor in March 1979, an event that became a pivotal moment for the nuclear industry and regulatory policy. Owned by Exelon and operated by Met Ed, the plant's operational Unit 1 was permanently shut down in 2019, marking the end of its service.

History and construction

The facility's development was led by the utility company General Public Utilities through its subsidiary Jersey Central Power & Light. Construction on Unit 1 began in 1968, with Unit 2 following shortly after. Both reactors were designed as pressurized water reactors supplied by the manufacturer Babcock & Wilcox. The Unit 1 reactor achieved criticality in 1974 and began commercial operation later that year, while Unit 2 entered service in 1978. The site's selection and licensing process involved the Atomic Energy Commission, the predecessor to the Nuclear Regulatory Commission.

Accident of 1979

On March 28, 1979, a combination of mechanical failures and human error led to a severe accident at the Unit 2 reactor. A stuck-open relief valve in the primary cooling system, compounded by misinterpreted instrument readings in the control room, caused a loss-of-coolant accident. This resulted in a partial core meltdown and the release of radioactive gases, primarily krypton and xenon, into the containment building and a small amount to the environment. The incident was classified as a Level 5 event on the International Nuclear Event Scale. The response involved state officials like Governor Dick Thornburgh and federal agencies including the Nuclear Regulatory Commission and the Department of Energy.

Technical specifications and design

Each unit housed a single pressurized water reactor manufactured by Babcock & Wilcox, with a distinctive once-through steam generator design. Unit 1 had a gross electrical output of 819 MW. The reactors used uranium dioxide fuel assemblies and were housed within large, dry containment buildings designed to withstand internal pressure. The plant's electrical output was fed into the PJM Interconnection grid. Key safety systems included emergency core cooling systems and extensive instrumentation monitored from a centralized control room.

Aftermath and decommissioning

Following the accident, Unit 2 was permanently shut down and defueled. A massive, decade-long cleanup project, managed by Bechtel and overseen by the Nuclear Regulatory Commission, was undertaken to remove damaged fuel and decontaminate the site. Unit 1 continued operating for decades under enhanced scrutiny and new regulations from the Nuclear Regulatory Commission. In 2019, facing economic pressures from natural gas competition, owner Exelon permanently ceased operations at Unit 1. The current decommissioning process, managed by EnergySolutions, is proceeding under the Nuclear Regulatory Commission's regulations, with spent fuel transferred to on-site dry cask storage.

Cultural and political impact

The accident profoundly influenced public perception, galvanizing the anti-nuclear movement and inspiring protests like those at the Seabrook Station Nuclear Power Plant. It became a central plot point in films such as The China Syndrome and was extensively covered by media including The New York Times. Politically, it led to the formation of the Kemeny Commission, which issued a scathing report on industry practices. The event directly spurred the creation of new safety protocols by the Nuclear Regulatory Commission and influenced legislation, contributing to a decades-long hiatus in new reactor orders in the United States.

Category:Nuclear power stations in Pennsylvania Category:Buildings and structures in Dauphin County, Pennsylvania Category:1968 establishments in Pennsylvania Category:2019 disestablishments in Pennsylvania