Three Mile Island supplies Microsoft data centers with electricity

The owner of the decommissioned Three Mile Island nuclear power plant said Friday that it plans to restart the reactor as part of a 20-year agreement that will see technology giant Microsoft purchase its electricity to power its data centers with carbon-free energy.

Constellation Energy's announcement comes five years after its then-parent company Exelon closed the power plant on the grounds that it was loss-making.

The power plant, located on an island in the Susquehanna River just outside Harrisburg, was the scene of the worst commercial nuclear accident in the United States in 1979. The accident destroyed one reactor (Block 2), while only one functioning reactor (Block 1) remained in the power plant.

The purchase of the electricity is intended to help Microsoft fulfill its commitment to be “carbon negative” by 2030.

Constellation hopes to bring Unit 1 online in 2028 and will seek a license extension from regulators to extend the plant's operation until at least 2054. Restarting the Unit 1 reactor will require approval from the U.S. Nuclear Regulatory Commission and approvals from state and local authorities, Constellation said.

In preparation for the restart of Unit 1, “significant investments” are needed to restore the plant, including the turbine, generator, main transformer and cooling and control systems, Constellation said.

The agreement came amid efforts by the Biden administration, states and utilities to rethink the use of nuclear energy to mitigate the effects of climate change and limit the energy sector's greenhouse gas emissions that contribute to global warming.

Last year, Georgia Power began generating electricity from America's first nuclear reactor in decades, built from scratch after the Three Mile Island accident killed interest in building new reactors.

Microsoft and Constellation did not disclose the terms of the agreement. Before its shutdown in 2019, Unit 1 had a power generation capacity of 837 megawatts, enough to power more than 800,000 homes, Constellation said.

The destroyed Unit 2 is sealed and its two cooling towers are still standing. The core was shipped to the U.S. Department of Energy's Idaho National Laboratory years ago. What remains inside the containment vessel remains highly radioactive and encased in concrete.