US Exelon said on 8 May that it would shut the last reactor at the Three Mile Island nuclear plant on 30 September because of legislative inaction on a nuclear subsidy bill in Pennsylvania.

"With only three legislative session days remaining in May and no action taken to advance House Bill 11 or Senate Bill 510, it is clear a state policy solution will not be enacted before 1 June," Exelon said in a release, referring to the proposed nuclear subsidy bills.

Exelon announced in May 2017 that it would shut the 45-year-old, 837MWe (net) pressurised water reactor in 2019 unless there was policy reform to support the plant. The company said it had to decide by 1 June to purchase fuel for the plant for its next operating cycle.

In recent years, electricity prices have been depressed by cheap natural gas from shale fields and increased use of renewable power, making some nuclear plants uneconomic resulting in the closure of several reactors over the past five years. Several states, including New York, Illinois, Connecticut and New Jersey have already adopted nuclear subsidies to keep their reactors in service while lawmakers in Pennsylvania and Ohio are still considering legislation.

In April, Exelon Generation filed the federally required Post Shutdown Decommissioning Activities Report detailing plans for TMI after its final shutdown, including transitioning staff in three phases down to 50 full-time employees by 2022. In the filing, Exelon Generation selected “SAFSTOR,” one of three decommissioning options for the plant, and outlined a plan to dismantle large components, including the site cooling towers, beginning in 2074.

"Even while we continue to safely operate Three Mile Island at industry-leading levels, we have a responsibility to prepare the plant, along with our community and our employees, for decommissioning," said site vice president Edward Callan said. "At the same time, we are actively engaged with stakeholders and policymakers on a solution to preserve Pennsylvania's nuclear facilities and the clean, reliable energy and good-paying jobs they provide … However, time is not on our side."

Pennsylvania has nine reactors at five sites – Beaver Valley, Limerick, Peach Bottom, Susquehanna and Three Mile Island. Together they produce nearly 40% of the state's total electricity generation and just over 93% of its zero-emissions energy.

 FirstEnergy has also announced plans for early retirement of its two-unit Beaver Valley plant in 2021. Legislation updating the Pennsylvania Alternative Energy Portfolio Standards Act to recognise nuclear energy for its significant contribution to the state's zero-carbon energy production was introduced in the state's legislature in March.

Photo: Three Mile Island 1 (Credit: Exelon Generation)