Notorious US nuclear site Three Mile Island to be reopened under deal with Microsoft

The owner of the decommissioned Three Mile Island nuclear power plant in the United States has announced 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 Friday comes five years after then-parent company Exelon closed the plant, citing loss-making nature and Pennsylvania state lawmakers refusing to subsidize it.

The plan to restart the first reactor block at Three Mile Island comes at a time of nuclear power renaissance. Politicians are increasingly pinning their hopes on nuclear power to save the ailing power supply, avoid the worst effects of climate change and meet the growing electricity demand of data centers.

The power plant 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), but only one functioning reactor (Block 1) remained in the plant.

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

Microsoft declined to say which of its data centers will be powered by the nuclear plant, but the Mid-Atlantic power grid stretches from Virginia, a data center hub for Microsoft and other tech giants, to Ohio, where Microsoft is planning a new data center complex outside Columbus.

Constellation hopes to bring Unit 1 online in 2028.

Restarting the reactor will require approval from the U.S. Nuclear Regulatory Commission and permits from state and local authorities, Constellation said.

To bring Unit 1 back online, Constellation will spend $1.6 billion (£1.2 billion) to restore equipment, including the turbine, generator, main transformer, and cooling and control systems.

At present, no efforts are being made to obtain state or federal subsidies, they said.

Microsoft and Constellation have not disclosed the terms of their agreement.

Jacopo Buongiorno, a professor of nuclear science and engineering and director of the Center for Advanced Nuclear Energy Systems at MIT, said Microsoft would likely pay above-market prices for carbon-free, reliable electricity.

Restarting the power plant is realistic but not easy, said Buongiorno.

“It all depends on the condition of the components and systems,” he said.

If the facilities are well maintained during the closure, the process will be relatively smooth, Buongiorno said.

A Constellation spokesman said the power plant itself was in excellent condition.

Constellation's announcement comes after a wave of coal and nuclear power plant closures over the past decade as competition from cheap natural gas flooded electricity markets.

This has led to warnings that the United States is facing an electricity security crisis.

At the same time, demand for data centers from technology giants such as Meta, Amazon, Microsoft and Google to provide cloud computing and digital services such as artificial intelligence systems is increasing rapidly.

The agreement between Constellation and Microsoft also came amid efforts by the Biden administration, states and utilities to rethink the use of nuclear energy to limit the energy sector's climate-damaging greenhouse gas emissions.

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

Before its shutdown in 2019, Three Mile Island's Unit 1 had a generating capacity of 837 megawatts, enough to power more than 800,000 homes, Constellation said.

The destroyed Block 2 is sealed, its two cooling towers are still standing.

Its core was delivered to the U.S. Department of Energy's Idaho National Laboratory years ago.

The remains inside the containment vessel remain highly radioactive and encased in concrete.