Shuttered Three Mile Island nuclear plant back online to power Microsoft data center

A reactor at the notorious Three Mile Island nuclear power plant near Middletown, Pennsylvania, will be going back into operations starting in 2028 in order to power Microsoft’s energy-hungry new data centers.

The reactor starting back up is Unit 1. In 1979, the adjacent reactor, Unit 2, experienced a partial meltdown after a failure kept water pumps from removing heat from the reactor core, according to the U.S. Nuclear Regulatory Commission. Unit 2 was decommissioned shortly thereafter.

Unit 1 ran until Sept. 20, 2019, when it was shut down by the Exelon Corporation, according to NPR. 

Officials from the energy company Constellation, which was spun off from Exelon in 2022 and which has owned Unit 1 since 1999, announced Friday that they had signed a 20-year agreement with Microsoft to start Unit 1 backup in order to power a growing system of Microsoft data centers.

The reactor is expected to produce 835 megawatts of electricity once it resumes operation.

Doing so “requires an abundance of energy that is carbon-free and reliable every hour of every day, and nuclear plants are the only energy sources that can consistently deliver on that promise. Before it was prematurely shuttered due to poor economics, this plant was among the safest and most reliable nuclear plants on the grid, and we look forward to bringing it back,” Constellation CEO Joe Dominguez said in a company statement.

Constellation plans to invest in equipment at the plant, including the cooling systems, the turbine, the generator, and the main power transformer, before the facility goes back online in 2028. Reopening the reactor also requires the approval of the federal NRC.

Using nuclear power is part of Microsoft corporate plans to end its use carbon-based energy by 2030, according to The Associated Press. State officials and Constellation touted the economic benefits of a reopened Three Mile Island for Pennsylvanians.

The reopened reactor “will safely utilize existing infrastructure to sustain and expand nuclear power in the Commonwealth while creating thousands of energy jobs and strengthening Pennsylvania’s legacy as a national energy leader,” Gov. Josh Shapiro, a Democrat, said in the statement.