Constellation Energy to restart Three Mile Island for Microsoft AI power deal

Constellation Energy announced a 20-year power purchase agreement with Microsoft to restart Unit 1 of the Three Mile Island nuclear plant in Londonderry, Pennsylvania, shut since 2019 for economic reasons unrelated to the 1979 partial meltdown at the site’s separate Unit 2. The reactor, to be renamed the Crane Clean Energy Center, would supply roughly 835 megawatts of carbon-free power, with the deal committing the output entirely to Microsoft’s data centres rather than the general grid.

Constellation said the restart still required approval from the Nuclear Regulatory Commission following a full safety and environmental review, plus state and local permits, and put the expected in-service date at 2028. The company separately said it would seek a licence renewal to extend the plant’s operating life to at least 2054, and estimated the project would create around 3,400 direct and indirect jobs and add roughly $16 billion to Pennsylvania’s economy.

The agreement was the clearest signal to date that AI data-centre demand had begun reshaping decisions about US electricity infrastructure that had been considered settled: a plant taken offline as commercially unviable was being revived specifically because a single large customer’s compute needs made the economics work again, without public subsidy driving the decision. It followed a wave of hyperscaler interest in nuclear power as a source of firm, carbon-free electricity able to run continuously alongside data-centre load, and preceded a series of comparable deals by other AI developers and utilities pursuing new or restarted reactors, small modular designs and long-term power contracts through 2025 and 2026. It also drew attention to the regulatory timeline nuclear restarts require, in contrast to the pace at which new data-centre capacity itself was being built.