Microsoft is backing a proposed restart of Three Mile Island’s Unit 1—not the Unit 2 reactor involved in the 1979 accident—through a 20-year power purchase agreement with Constellation. The plan has drawn scrutiny over nuclear oversight, data-center demand, public financing and what the companies’ carbon-free energy claims mean in practice. The sources available for this article do not establish how widespread public opposition is, or whether the restart has received final regulatory authorization.
Which Three Mile Island reactor is proposed for restart?
The plan concerns Unit 1, which stopped operating on September 20, 2019. The partial meltdown in March 1979 occurred in Unit 2, a separate reactor at the same site. The Nuclear Regulatory Commission (NRC) distinguishes Unit 1’s later closure from the Unit 2 accident and its lasting effect on nuclear regulation.
In its September 2024 announcement, Constellation described Unit 1 as a fully independent facility whose long-term operation was not affected by the Unit 2 accident. That is the company’s characterization, not an independent NRC safety finding about the proposed restart.
What did Microsoft and Constellation agree to?
On September 20, 2024, Microsoft and Constellation announced a 20-year power purchase agreement (PPA) tied to the planned return of Unit 1. Constellation proposed renaming the facility the Crane Clean Energy Center and said it expected the plant to serve customers again in 2028.
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Microsoft says the electricity will help match its data-center consumption in the PJM grid region with carbon-free energy. That is a grid-level purchasing and matching rationale; the available accounts do not identify particular Microsoft data centers that would receive power through a dedicated connection. Nor does the company’s stated goal, by itself, establish a specific reduction in project-attributable emissions.
Constellation said the plant would provide approximately 835 megawatts of carbon-free generation capacity in its 2024 release. The Associated Press separately reported a pre-shutdown capacity of 837 MW in 2024; those attributed figures should not be treated as identical measures.
What is known about the price and public financing?
The AP reported in 2024 that Microsoft and Constellation had not disclosed the PPA’s price or detailed terms. A Reuters estimate of $110–115 per megawatt-hour, cited in a 2025 U.S. House hearing report, is an estimate—not a disclosed contract price.
The financing picture also changed after the initial announcement. Constellation said in 2024 that it was not then seeking state or federal subsidies. On November 18, 2025, the AP reported that the U.S. Department of Energy would provide a $1 billion loan to help finance the restart; the loan terms had not been released in that account. The earlier statement should not be read as a description of all later financing.
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What has been projected for jobs and the Pennsylvania economy?
Constellation’s 2024 announcement cited a Brattle Group economic-impact study commissioned by the Pennsylvania Building & Construction Trades Council. Its figures are projections, not measured results:
- 3,400 direct and indirect jobs projected by the Brattle Group in 2024.
- More than $3 billion in state and federal taxes projected by the Brattle Group in 2024.
- $16 billion added to Pennsylvania GDP projected by the Brattle Group in 2024.
These estimates describe anticipated impacts if the project proceeds; they do not show that the jobs, tax revenue or GDP growth have already materialized.
Is the restart approved?
The project requires NRC safety and environmental review as well as state and local permits, according to Constellation’s 2024 announcement. The NRC’s facility-page summary describes restart oversight and a public-comment period on a draft environmental assessment that ended July 8, 2026. The available summary does not establish the outcome of that process or final authorization to restart. Regulatory review is neither proof of danger nor proof that the project has been approved.
The milestones show why announced targets should be treated as plans rather than a completed restart:
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| Date | Milestone |
|---|---|
| September 20, 2019 | Unit 1 ceased operations, according to the NRC. The AP reported that its then-parent company shut it down because it was losing money. |
| September 20, 2024 | Constellation announced the Microsoft PPA, restoration plan and expected 2028 service date; it said regulatory reviews and permits were required. |
| May 2025 | The NRC facility search result recorded approval to change the facility name from Three Mile Island Nuclear Station, Unit 1, to Christopher M. Crane Clean Energy Center, and described specific restart oversight. A name change is not restart authorization. |
| November 18, 2025 | The AP reported the planned $1 billion DOE loan and said Constellation hoped to bring the plant online in 2027. That was a dated target, earlier than the 2028 target in the 2024 announcement. |
| Through July 8, 2026 | The NRC facility-page summary described public comments on a draft environmental assessment through this date; the summary does not report a final restart decision. |
Why does the proposal invite scrutiny?
Accident history and risk perception
The Three Mile Island name is inseparable from the Unit 2 accident for many people, even though the proposed restart concerns Unit 1. Keeping the units distinct is essential: the site’s history is relevant to public debate, but the 1979 event was not an accident at the reactor proposed for restart.
Private data-center demand and undisclosed terms
The PPA is connected to Microsoft’s growing data-center electricity needs, but the full commercial terms were not public in the AP account. That leaves questions about the deal’s price and allocation of benefits unanswered. The evidence supports a purchase and grid-matching arrangement, not a claim that the plant will physically feed a named Microsoft data center.
Federal financing and who bears risk
The reported DOE loan makes the government’s role part of the debate alongside the private agreement. Assessing that role requires the loan’s terms, which the AP said had not been released, as well as clarity about who bears project risks and who receives its benefits.
Climate claims versus demonstrated outcomes
Microsoft and Constellation present the project as a source of carbon-free electricity and a contribution to grid decarbonization. Those are company-stated aims. The available sources do not establish a realized, project-specific emissions reduction, so the claim should not be confused with a measured result.
How can readers assess the competing policy arguments?
| Question | Case for the restart | Reason for scrutiny |
|---|---|---|
| Safety and oversight | Supporters can point to the NRC review and oversight process required before restart. | Review is still a process; readers can look for the agency’s findings, inspection information and required permits rather than treating either approval or danger as settled. |
| Who pays? | A long-term electricity buyer and reported federal loan could support a project intended to return generation to service. | The PPA price and detailed terms were not disclosed in the AP account, and the AP said DOE loan terms had not been released. |
| Who benefits? | The commissioned Brattle study projects jobs, tax revenue and state economic activity. | Those are forecasts cited by Constellation, not verified outcomes; the study was commissioned by a trade council. |
| What is the grid effect? | The companies say the generation will help match data-center use with carbon-free electricity. | Grid matching is not the same as a dedicated physical supply to a specific data center or proof of a particular net emissions reduction. |
| How does the site’s history matter? | Unit 1 is distinct from the reactor involved in the 1979 accident. | The shared site and name make the accident a continuing factor in public confidence and debate. |
Constellation CEO Joe Dominguez argued in the 2024 release that data centers require abundant, reliable, carbon-free power and that nuclear plants can provide it consistently. Microsoft energy vice president Bobby Hollis called the agreement a milestone in the company’s effort to decarbonize the grid. Those statements explain the companies’ rationale; they do not settle questions about project safety, the PPA’s economics or its actual climate impact.
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