Microsoft Powers Data Centers with Three Mile Island Nuclear

Data centers’ need for clean electricity is so ravenous that a shuttered nuclear reactor at Three Mile Island—the site of the worst nuclear disaster in U.S. history—may be revived just to power them.

Constellation Energy in September announced that it plans to restart Unit 1 at Three Mile Island, which will supply 835 megawatts to grid operator PJM. Tech giant Microsoft will buy the power produced at Three Mile Island to help match the power consumed by its data centers in the PJM Interconnection, according to a 20-year power purchase agreement it made with Constellation.

The Unit 1 reactor was shuttered in 2019 for economic reasons and sits adjacent to Unit 2, which was destroyed in 1979 in a partial meltdown. Restarting Unit 1 will require Constellation to surmount engineering and regulatory hurdles, and address the public relations challenge of overcoming the site’s historical link to nuclear disaster.

If the plan comes to fruition, Three Mile Island Unit 1 could be the second nuclear reactor in the world to be resurrected. The first—the Palisades Nuclear Plant in Covert, Mich., which shuttered in May 2022—is currently on track to return to operations in 2025. According to media reports, the single nuclear reactor at the Duane Arnold Energy Center near Palo, Iowa, which ceased operations in 2020, might also be brought back online.

The burgeoning trend could birth a new area of expertise: How to restart a nuclear reactor.

Reviving Three Mile Island for Data Centers

Constellation aims to have Unit 1 at Three Mile Island up and running in 2028. To prepare for the restart, significant investments will be made to restore the plant, including its turbine, generator, main power transformer, and cooling and control systems, according to Constellation.

The rationale for restarting a nuclear plant rather than building one from scratch is easy to see, says Kathryn Huff, an associate professor of nuclear, plasma, and radiological engineering at the University of Illinois, and a former assistant secretary of nuclear energy at the U.S. Department of Energy. For example, developing a new nuclear site would involve figuring out how to dissipate the reactor’s heat. That’s already been sorted at Three Mile Island, located near Middletown, Penn., which has an existing ecosystem in place.

“I think one of the most important features is that the Susquehanna River’s right there. They have the ultimate heat sink already set up,” says Huff. Crucially, the island also has high-voltage transmission lines in place, along with all the other infrastructure necessary to connect the plant to the power grid.

It helps that the recently closed reactor operated for decades under a license from the U.S. Nuclear Regulatory Commission, which oversees the industry. The most straightforward way to get the reactor back online, Huff says, is for Constellation to seek to restore the old license and to bring the plant up to the standard at which it ran until 2019….