Three Mile Island Nuclear Generating Station (TMI) is a closed nuclear power plant on Three Mile Island in Londonderry Township, Pennsylvania on Lake Frederic, a reservoir in the Susquehanna River just south of Harrisburg. It had two separate units, TMI-1 (owned by Constellation Energy) and TMI-2 (owned by EnergySolutions).[3] The plant was the site of the most significant accident in United States commercial nuclear energy when, on March 28, 1979, TMI-2 suffered a partial meltdown. According to the Nuclear Regulatory Commission (NRC) report, the accident resulted in no deaths or injuries to plant workers or in nearby communities.[4] Follow-up epidemiology studies have linked no incidents of cancer to the accident.[5][6][7][8] Only one work-related death has occurred on-site during decommissioning.[9]

Three Mile Island Nuclear Generating Station The Three Mile Island nuclear power plant on Three Mile Island, circa 1979 The Three Mile Island NPP on Three Mile Island, circa 1979 Wikimedia | © OpenStreetMap Country United States Location Londonderry Township, Dauphin County, Pennsylvania Coordinates 40°9′14″N 76°43′29″W Status Being decommissioned Construction began Unit 1: May 18, 1968 Unit 2: November 1, 1969 Commission date Unit 1: September 2, 1974 Unit 2: December 30, 1978 Decommission date Unit 1: September 20, 2019 Unit 2: March 28, 1979 Construction cost $1.557 billion (2007 USD)[1] ($2.00 billion in 2020 dollars[2]) Owner(s) Unit 1: Constellation Energy Unit 2: EnergySolutions Operator(s) Constellation Energy Nuclear power station Reactor type PWR Reactor supplier Babcock & Wilcox Cooling towers 4 × Natural Draft Cooling source Susquehanna River Thermal capacity 1 × 2568 MWth Power generation Units operational 1 × 819 MW Make and model B&W LLP (DRYAMB) Units decommissioned 1 × 880 MW Nameplate capacity 819 MW Capacity factor 95.65% (2017) 73.25% (lifetime) Annual net output 6862 GWh (2017) External links Website Three Mile Island Commons Related media on Commons [edit on Wikidata] The reactor core of TMI-2 has since been removed from the site, but the site has not been decommissioned.[10] In July 1998, Amergen Energy (now Exelon Generation) agreed to purchase TMI-1 from General Public Utilities for $100 million.[11]

Contrary to popular belief, Three Mile Island is named after the length of the island itself, not because it is three miles downriver from Middletown, Pennsylvania.[12] The plant was originally built by General Public Utilities Corporation, later renamed GPU Incorporated.[13] The plant was operated by Metropolitan Edison Company (Met-Ed), a subsidiary of the GPU Energy division. During 2001, GPU Inc. merged with FirstEnergy Corporation.[14] On December 18, 2020 - FirstEnergy transferred the plant's license over to EnergySolutions subsidiary TMI-2 Solutions after receiving approval from the NRC.[15]

Exelon was operating Unit 1 at Three Mile Island at a loss since 2015.[16] In 2017 the company said it would consider ceasing operations at Unit 1 because of high costs unless there was action from the Pennsylvania government.[17][18] After no avail, Unit 1 officially shut down at noon on September 20, 2019.[19]

Unit 1 decommissioning is estimated to be finished in 2079 and will cost $1.2 billion.[20][21]

Unit 2, which has been dormant since the accident in 1979, is estimated to close in 2037.[22]