They're planning to restart the Three Mile Island nuclear power plant to power Microsoft's cloud and AI data centers

If everything goes to plan, a nuclear reactor at the famous Three Mile Island power plant in Pennsylvania—the site of a major accident in the '70s—will be restarted by power company Constellation Energy to fulfill an agreement with Microsoft for carbon-free energy to power its data centers.

The reactor coming back online is not the one that had a partial meltdown in 1979, which has remained dormant since the accident. That was TMI-Unit 2. The adjacent reactor, TMI-Unit 1, went back into operation in 1985 and continued to operate until 2019, when it was shut down due to "poor economics," according to Constellation.

After refurbishing it and obtaining the necessary federal and state approvals, Constellation hopes to have TMI-Unit 1 operating by 2028, and says that restarting the reactor will "add approximately 835 megawatts of carbon-free energy to the grid." It's also renaming the plant "Crane Clean Energy Center" after Chris Crane, a nuclear energy "titan" who died earlier this year.

Both Pennsylvania politicians and the US Department of Energy have praised Constellation's plan. Dr Michael Goff, acting assistant secretary of the federal agency's Office of Nuclear Energy, said that "always-on, carbon-free nuclear energy plays an important role in the fight against climate change and meeting the country's growing energy demands."

Microsoft's data centers are the infrastructure that support its cloud storage and computing services, including new and notoriously energy-hungry AI processing. Microsoft VP of energy Bobby Hollis says that this power agreement, the largest it's ever made with Constellation, is a "major milestone in Microsoft's efforts to help decarbonize the grid." Separately, we know that Microsoft has been looking into using "small modular reactors" and "microreactors" to power its data centers.

Microsoft founder Bill Gates is also in the nuclear energy business: A company he founded in 2006, TerraPower, broke ground on a new plant in Wyoming earlier this year.

"The US hasn't needed much new electricity—but with the rise in a variety of things from electric cars and buses to electric heat pumps to heating homes, demand for electricity is going to go up a lot," Gates told NPR in June. "And now these data centers are adding to that. So the big tech companies are out looking at how they can help facilitate more power, so that these data centers can serve the exploding AI demand."