Microsoft deal backs planned restart of Three Mile Island Unit 1

Constellation and Microsoft have signed a 20-year power purchase agreement intended to bring Three Mile Island Unit 1 back into service. Announced on 20 September 2024, the project would rename the Pennsylvania facility the Crane Clean Energy Center.

The contract covers the plant’s full output at a fixed price. Constellation’s investor presentation puts planned capacity at 835 megawatts and targets a 2028 restart.

Microsoft describes the deal as adding carbon-free electricity to the PJM regional grid. The planned output would help match its data-centre electricity use with carbon-free generation.

The reactor and the approvals

Unit 1 closed for economic reasons in 2019. It is separate from neighbouring Unit 2, which shut down after the 1979 accident and is being decommissioned.

Constellation plans roughly US$1.6 billion of capital spending. Its presentation says inspections of the steam generator, main generator and main transformer are complete, along with restoration of the training and simulator building. Further equipment work, hiring and certification remain ahead.

The restart requires Nuclear Regulatory Commission approval following safety and environmental review, plus state and local permits. Constellation also intends to seek a separate licence renewal to support operation through at least 2054.

The company’s schedule also includes a PJM interconnection study and anticipated federal approval to connect in spring 2028. Each remains subject to the relevant approval process.

Part of a wider energy mix

Microsoft says nuclear power will complement a contracted renewable-energy portfolio of 34 gigawatts across 24 countries. Its approach also includes wind, solar, geothermal, storage and other technologies.

The agreement links a long-term electricity buyer to a plant-restoration project, while leaving engineering and approval work to be completed before power can flow.

Illustration: Sulat. Logos: Microsoft, Constellation.