A nuclear reactor at Pennsylvania’s Three Mile Island is being prepared for an unprecedented restart under a 20-year power agreement designed to supply carbon-free electricity associated with Microsoft’s rapidly expanding data-center operations.
Microsoft is not directly restarting or operating the reactor. Constellation Energy owns the facility and is carrying out the multibillion-dollar restoration project, while Microsoft has agreed to purchase its electricity. The site has been renamed the Christopher M. Crane Clean Energy Center and could return to service in the second half of 2027 if the remaining regulatory, technical and grid-connection requirements are completed.
Microsoft Signed a 20-Year Power Deal
Constellation announced the agreement with Microsoft in September 2024. Under the arrangement, Microsoft will purchase energy from the restarted reactor for 20 years, providing the long-term financial commitment needed to justify bringing the closed plant back into operation.
The deal is connected to Microsoft’s growing need for reliable, round-the-clock, low-carbon electricity. Artificial-intelligence systems require enormous computing capacity, and the data centers running those systems consume electricity continuously for servers, storage, networking and cooling.
Unlike wind and solar generation, which vary with weather and time of day, nuclear reactors can produce large amounts of power around the clock. That makes nuclear energy increasingly attractive to technology companies seeking both dependable electricity and progress toward emissions goals.
The original announcement and project details are available through Constellation Energy’s Crane Clean Energy Center announcement.
The Reactor Has Not Restarted Yet
Headlines may make the project sound as though Three Mile Island is already generating power again, but the reactor remains offline as of July 2026.
Constellation initially targeted a 2028 restart. The company later said restoration work was moving ahead of schedule and that the reactor could be technically ready during the second half of 2027. Federal energy regulators granted a key grid-related waiver in June 2026, removing one potential obstacle to delivering the electricity.
A restart still depends on regulatory approvals and successful completion of extensive inspections, repairs and testing. No fully shut-down commercial nuclear power plant in the United States has previously returned to service after entering decommissioning, making the project highly unusual.
This Is Not the Reactor That Melted Down in 1979
The Three Mile Island name is inseparable from the partial nuclear meltdown that occurred on March 28, 1979. However, the reactor being restored is not the unit involved in that accident.
The 1979 event occurred at Unit 2. That reactor never operated again and is not part of Microsoft’s power agreement.
The restart concerns Unit 1, a separate reactor at the same site. Unit 1 returned to service after the 1979 accident, operated for decades and closed in September 2019 because it was struggling financially in an electricity market dominated by inexpensive natural gas.
Constellation says Unit 1 had a strong operating record before its economic closure. The Nuclear Regulatory Commission now lists the facility under its new Crane Clean Energy Center name.
How Much Electricity Will It Produce?
The restored reactor is expected to generate approximately 835 megawatts of electricity.
Constellation has said that output is comparable to the electricity used by more than 800,000 homes. The actual power will enter the regional grid rather than travel through a dedicated wire directly from the plant to one Microsoft data center. Microsoft will receive the contracted energy and environmental value through the regional power system.
This distinction matters because the plant will still participate in the broader electricity market. Its output can support regional demand while Microsoft financially contracts for the generation needed to match its operations.
Why AI Is Driving Technology Companies Toward Nuclear Power
Modern data centers are already major electricity users, but generative AI has increased demand further.
Training a large AI model can require thousands of high-performance processors operating together for extended periods. Once deployed, the model continues consuming power every time users submit questions, generate images, analyze data or run AI-assisted business applications.
The servers also produce substantial heat, requiring continuous cooling. As companies build larger AI campuses, electricity availability can become as important as access to land, chips and network connections.
Microsoft is not the only technology company seeking nuclear energy. Other major firms have entered agreements involving existing nuclear plants, advanced reactors and small modular reactor projects as the industry competes for dependable, low-emissions electricity.
The Three Mile Island agreement is particularly significant because it is helping revive a reactor that had already shut down rather than merely extending the life of an operating plant.
The Restart Will Require Major Restoration Work
A nuclear power plant cannot be restarted by simply refueling the reactor and switching it on.
Constellation must restore or replace equipment that has been inactive since 2019. The work includes the turbine, generator, transformer, cooling systems, control equipment and other plant infrastructure. The company must also inspect safety-related systems, reload nuclear fuel, recruit and train licensed operators and demonstrate that the plant complies with current requirements.
The company has said the project will create or restore hundreds of permanent jobs and support additional construction and skilled-trade positions during recommissioning.
Federal Regulators Still Play a Central Role
Constellation cannot independently declare the reactor ready and begin generating electricity.
The Nuclear Regulatory Commission is reviewing the changes, inspections and licensing actions required for the plant to operate again. The agency has held public meetings and is evaluating safety and environmental issues associated with the restart.
In June 2026, the NRC reportedly concluded that the proposed restart would not create significant environmental effects, moving the project closer to final approval. That finding did not by itself mean the reactor could immediately resume operation.
The Federal Energy Regulatory Commission also became involved because Constellation faced a potential grid-connection delay. PJM Interconnection had warned that broader transmission upgrades might prevent full delivery of the reactor’s output until 2031. FERC granted a waiver allowing Constellation to transfer certain grid-injection rights from another generating station, helping preserve the targeted 2027 restart schedule.
The Project Is Receiving Federal Financial Support
The U.S. Department of Energy announced a $1 billion loan to help finance the restart in November 2025.
The broader project has been valued at approximately $1.6 billion. Federal support is intended to reduce financing costs and help preserve a large source of domestic nuclear generation. Supporters argue that the plant will strengthen grid reliability, create jobs and provide low-carbon power for growing industries.
Critics question whether public financing should support an energy project connected to one of the world’s wealthiest technology companies. Others warn about cost overruns, nuclear waste and the complexity of restoring equipment that has been shut down for years.
Nuclear Power Is Low-Carbon, but Not Risk-Free
Nuclear plants produce electricity without the direct carbon emissions associated with coal- or gas-fired generation.
That advantage makes nuclear energy valuable to companies trying to reduce operational emissions while keeping data centers online every hour of the day. Existing nuclear sites also have transmission infrastructure and local workforces that may make restoration faster than developing an entirely new large power plant.
However, nuclear energy continues to raise concerns about radioactive waste, accident risk, high construction costs and long project timelines. Three Mile Island carries additional emotional and historical weight because of the 1979 accident, even though the unit being restored was not the damaged reactor.
The restart will therefore receive far more public attention than an ordinary power-purchase agreement.
Will the Electricity Be Used Only for AI?
Microsoft’s contract supports its data-center electricity needs, including the growing demand associated with AI, but it would be misleading to say every electron generated at the plant will be used exclusively for artificial intelligence.
Electricity from the reactor will enter the regional grid. Microsoft’s agreement is a financial and energy-purchasing arrangement that helps match the company’s demand with the plant’s production.
Microsoft operates data centers for cloud computing, storage, business applications, communications and many other services alongside AI. The electricity associated with the contract will support that wider digital infrastructure.
Still, the rapid expansion of AI is a major reason technology companies are seeking unusually large and long-term sources of power.
Why the Restart Matters Beyond Microsoft
The project could become a model for other closed nuclear plants.
Utilities and technology companies are watching to see whether an economically retired reactor can be restored safely, licensed successfully and returned to service within a realistic budget. A successful restart could encourage similar efforts at other sites, while delays or major cost increases could make future projects harder to justify.
It also demonstrates how technology companies are becoming major forces in energy planning. Their data centers can require as much electricity as large industrial facilities, giving them the financial power to extend the life of existing generators or support entirely new projects.
The Main Point
Three Mile Island has not yet restarted, and Microsoft is not personally operating the facility.
Constellation Energy is restoring the undamaged Unit 1 reactor under a 20-year electricity agreement with Microsoft. The project is targeting a restart in late 2027, subject to final approvals, inspections, testing and successful completion of the plant’s restoration.
The deal illustrates how dramatically AI is changing electricity demand. A reactor that closed in 2019 because it could not compete economically may return less than a decade later because data centers need enormous amounts of reliable, low-carbon power.
