Three Mile Island Data Center Deal and Ownership
The Three Mile Island nuclear plant in Pennsylvania is being repurposed for a large data center project led by Constellation Energy and Microsoft. The facility, known as TMI-1, is the surviving reactor from the site famous for the 1979 partial meltdown. Constellation, the largest US nuclear operator, is negotiating a 20-year power purchase agreement to supply Microsoft with carbon-free electricity for AI and cloud workloads. The deal is part of Microsoft's broader strategy to secure clean, reliable power for its expanding data center portfolio as reported by Forbes.
Constellation Energy plans to restart the TMI-1 reactor, which has been offline since 2019, to serve the data center demand. The company has submitted license renewal applications and is working with regulators to align the restart timeline with Microsoft's infrastructure buildout. The project highlights a growing trend of hyperscalers partnering with nuclear operators to meet the power-intensive needs of artificial intelligence training and large-scale computing.
Power Capacity and AI Data Center Demand
The TMI-1 reactor has a net electrical capacity of approximately 835 megawatts, enough to power hundreds of thousands of homes. Microsoft has indicated that the clean energy from Three Mile Island will directly support its AI infrastructure, including Azure cloud services and OpenAI-related workloads. The deal is one of the largest known examples of a tech company locking in nuclear power specifically for AI data centers.
AI data centers require significantly more electricity per rack than traditional facilities, driving companies to seek long-term power agreements with stable baseload sources. Nuclear energy offers a low-carbon, 24/7 power supply that aligns with Microsoft's sustainability goals and its commitment to match 100 percent of its electricity consumption with zero-carbon sources per Microsoft's official sustainability documentation. The Three Mile Island project is being watched closely as a potential model for pairing legacy nuclear plants with modern AI infrastructure.
Timeline, Regulatory Status, and Site Details
Constellation Energy has targeted a restart of the TMI-1 reactor in the late 2020s, pending regulatory approvals and construction of dedicated transmission infrastructure. The U.S. Nuclear Regulatory Commission and state agencies are reviewing the restart application, which includes updated safety assessments and environmental reviews. The timeline remains contingent on permitting, grid interconnection studies, and finalizing the power purchase agreement terms.
The Three Mile Island site spans roughly 800 acres in Dauphin County, Pennsylvania, and includes existing switchyards and transmission connections that reduce new build costs. Microsoft and Constellation have not disclosed the exact financial terms of the deal, though industry analysts estimate the power agreement could be worth billions over its 20-year span based on filings available through the SEC EDGAR system. The project underscores the convergence of nuclear energy revival and AI-driven data center expansion in the United States.