The US Three Mile Island NPP in Pennsylvania is to close in 2019 in face of low natural gas prices, which make continued operation uncompetitive, plant owner Exelon said on 30 May. Exelon said it will close the plant unless the state adopts rules to compensate the company for benefits Exelon says nuclear power provides. New York and Illinois adopted rules in 2016 to provide payments to nuclear reactors to keep the units in service to help meet state carbon reduction goals and keep the jobs, taxes and fuel diversification the plants provide.

Three Mile Island employs about 675 people, produces enough electricity to power 800,000 homes and pays more than $1m in state property taxes a year, Exelon said. Despite producing 93% of Pennsylvania's emissions-free electricity and avoiding 37m tonnes of carbon emissions, the state’s nine nuclear power reactors are not included in the state's Alternative Energy Portfolio Standard, which includes 16 power sources including solar, wind and hydro energy, the company added.

Exelon said it is taking initial steps to shut down the plant, including informing key stakeholders including the regional transmission organisation PJM and the Nuclear Regulatory Commission (NRC). It will also immediately take one-time charges of $65-110m for 2017 and accelerate some $1-1.1bn in depreciation and amortisation between now and the shutdown date. Exelon will also terminate capital investment programmes required for the long-term operation of the plant and cancel 2019 fuel purchases and outage planning.

Low natural gas prices from shale formations such as Pennsylvania's Marcellus have kept power prices low, making it difficult for nuclear to compete with gas-fired generators in deregulated power markets in the US Northeast and Midwest. Since 2013, the USA has shut six reactors for economic reasons before their licenses expired in California, Florida, Nebraska, Vermont and Wisconsin, and plan to shut at least six more over the next five years.

In June 2016, Exelon announced plans for the early retirements of two NPPs in Illinois – Clinton and Quad Cities – due to a lack of progress on that state's energy policy. However, in December, the state introduced energy legislation that will ensure continued operation of the plants. Similarly, in August 2016, the New York Public Service Commission formally approved a Clean Energy Standard recognising the zero-carbon contribution of NPPs and ensuring continued operation of four that had been at risk of premature closure, including the James A Fitzpatrick plant, which Exelon then agreed to buy from Entergy.

Unit 1 of the Three Mile Island plant – which is built on an island in the Susquehanna River – began commercial operation in September 1974. It is a pressurised water reactor designed by Babcock and Wilcox. The unit is capable of generating 837MWe (net). Unit 2, owned by First Energy the site of the worst nuclear accident in US history in 1979, when the plant suffered a partial meltdown, leading to sweeping new rules for handling emergencies at nuclear sites. The plant was never re-opened. There were no fatalities from the accident, which released “significant” radiation into the air, according to NRC. Although 2m people were exposed to higher than normal levels of radiation, studies concluded that it had “negligible effects” on health or the environment, the commission said. However, no new nuclear reactors were ordered in the USA for the following three decades.