Microsoft & Constellationās Bid to Restart Three Mile Island
Microsoft has secured a dedicated nuclear power supply through a 20-year agreement with Constellation Energy to restart Unit 1 of Three Mile Island, now operating under the name Crane Clean Energy Center.
The facility, which shut down in 2019 due to financial constraints, is expected to begin operations in 2027, one year ahead of the original 2028 timeline.
The power purchase agreement (PPA), announced in September 2024, represents Microsoft’s response to mounting energy requirements from AI and cloud computing operations.
The tech giant’s emissions increased by 23.4% in fiscal year 2024, despite its 2020 commitment to achieve carbon negative status by 2030.
“As Microsoft continues its path to become a carbon negative company, this agreement brings a significant supply of new, reliable, carbon-free electricity back to the PJM power grid,” says Bobby Hollis, VP of Energy at Microsoft. “This will help address the grids’ capacity and reliability needs in the regions we operate.”
Accelerating the path to nuclear power
The nuclear facility previously operated as Unit 1 of the Three Mile Island Nuclear Generating Station until its closure in 2019.
Unit 2 at the same site experienced a partial meltdown in 1979, which the US Nuclear Regulatory Commission classifies as the most serious accident in US nuclear power plant history. The incident was rated Level 5 on the International Nuclear Event Scale, indicating wider consequences, though the World Nuclear Association states no injuries or adverse health effects occurred.
Unit 1 had gone offline for refuelling approximately one month before the Unit 2 accident and resumed operations in 1985.
Constellation maintains the reactor remains in what it describes as “excellent shape” despite its five-year shutdown period.
The company now anticipates the facility could restart in 2027 following approval of an early interconnection request by grid operator PJM. The company reports the facility has reached 65% staffing levels and achieved several technical milestones, including successful operation of the main generator and turbines.
“Today we begin a new chapter for reliable, emissions-free nuclear energy, returning thousands of good jobs and billions in economic opportunities for Pennsylvania families and businesses,” says Joe Dominguez, Constellation's President and CEO.
“With PJM's action, Microsoft's historic investment and strong support from Governor Shapiro, elected officials and members of this community, we're on track to make history ahead of schedule, helping America achieve energy independence, supercharge economic growth and win the global AI race.”
Microsoft hopes to confront data centre power requirements
The agreement reflects broader industry pressure as data centre operators confront escalating power demands.
UN Trade and Development projects the AI market will reach US$4.8tn by 2033 and McKinsey research indicates nearly 80% of organisations already deploy AI in at least one business function, while Gen AI adoption grew from 33% in 2023 to 71% in 2024.
Microsoft’s Chief Sustainability Officer, Melanie Nakagawa, acknowledged in February 2025 that the company’s sustainability timeline required adjustment.
“In 2020, Microsoft leaders referred to our sustainability goals as a ‘moonshot’, and nearly five years later, we have had to acknowledge that the moon has gotten further away,” she wrote in a blog post.
Nuclear power plants generate no greenhouse gas emissions during operation, positioning them as a viable solution for data centre operators seeking to maintain 24/7 operations whilst meeting carbon reduction targets.
Despite Microsoft investing in renewables, solar and wind power sources do not provide reliable enough power for continuous data centre operations.
Pennsylvania Governor Josh Shapiro shares: “My Administration has worked closely with Constellation and PJM on the Crane Clean Energy Center since 2023 in order to get this new generation online as quickly as possible, ensure the reliability of our grid and cement the Commonwealth's energy future.
“[Restarting Crane Clean Energy Center] will safely take advantage of existing infrastructure while creating thousands of energy jobs and strengthening Pennsylvania’s legacy as a national energy leader.”
The facility restart is projected to contribute US$16bn to Pennsylvania’s GDP, with the Nuclear Energy Institute viewing the project as validation of the nuclear industry’s capacity to meet rising energy demands.
“We congratulate Constellation, Microsoft and the state of Pennsylvania for doing something that seemed impossible just a few years ago: restarting a shuttered nuclear plant,” says Maria Korsnick, President and CEO of the Nuclear Energy Institute.
“The US nuclear industry is uniquely positioned to meet the rising demand for clean, reliable, and affordable energy. The Crane Clean Energy Center is a powerful example of how our industry is rising to the challenge.”
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