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Yes, the project is real—but Three Mile Island is not producing power again yet. Constellation Energy plans to restart the former Unit 1 reactor, now called the Christopher M. Crane Clean Energy Center, under a 20-year power-purchase agreement with Microsoft. Constellation is targeting commercial operation in 2027, but the Nuclear Regulatory Commission (NRC) still must approve licensing changes and the company must complete inspections, restoration work, upgrades and other readiness steps. The plan concerns Unit 1, not Unit 2, the reactor damaged in the 1979 accident.
What is actually being restarted?
The project covers Three Mile Island Unit 1, a separate pressurized-water reactor from Unit 2. Unit 1 began commercial operation in 1974 and permanently stopped generating electricity in September 2019 after more than four decades of operation. Its closure was an economic decision, not a result of the 1979 accident.
Constellation renamed the facility the Christopher M. Crane Clean Energy Center in 2025. If restored and relicensed, Unit 1 is intended to provide approximately 835 megawatts (MW) of electrical capacity. The reactor has a thermal capacity of about 2,568 megawatts, according to the NRC. Unit 2 remains associated with the accident and decommissioning history; the restart proposal does not reopen it.
Constellation announced the Microsoft agreement on September 20, 2024. The announcement launched a restoration project, not an immediate return to service.
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What Microsoft agreed to buy
Microsoft signed a 20-year power-purchase agreement (PPA) for electricity associated with the renewed plant. Constellation says the contract is intended to help match Microsoft’s data-center electricity use in the PJM regional grid with carbon-free nuclear generation. The original announcement is at Constellation’s project release.
This is not necessarily a dedicated wire from the reactor to a Microsoft campus. The plant would inject electricity into the interconnected PJM market, which covers much of the Mid-Atlantic and Midwest. Microsoft’s contract and associated accounting link its regional data-center demand with the plant’s generation, even though the physical electrons on the grid are continuously mixed.
The U.S. Energy Information Administration explains the relationship between the PPA, PJM and data-center demand in its analysis of nuclear power and data centers. A Microsoft facility covered by the arrangement does not have to sit next to Three Mile Island.
Why a technology company wants nuclear generation
Cloud and artificial-intelligence data centers consume electricity continuously. A large nuclear unit can provide steady output around the clock, with no direct carbon emissions during generation. That combination can help a company pursue emissions-reduction goals while adding workloads that may run day and night.
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Future demand is uncertain. The EIA notes that construction schedules, peak loads, efficiency gains and changes in computing workloads can alter data-center electricity forecasts. A long-term contract therefore provides a commercial anchor, but it does not eliminate market or demand risk.
What must happen before Unit 1 can operate
The NRC treats the proposal as a regulated restoration of a plant in SAFSTOR, not as a simple switch-on. The agency’s Crane Clean Energy Center project page identifies several separate requirements.
Restore the licensing basis
Constellation must obtain approval to restore the plant’s licensing basis to an operational status. That involves demonstrating that the technical specifications, safety programs and operating commitments support renewed generation.
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Inspect and restore equipment
Equipment must be returned to a condition suitable for safe operation. Reported work includes the turbine, generator, main power transformer, cooling systems and control systems. Inspections and testing must establish that components can perform as required after years outside power operation.
Complete required upgrades
The company must make upgrades needed to meet the proposed operating license basis. These can include changes identified through inspections, updated requirements or plant-specific reviews.
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Complete environmental and licensing proceedings
Environmental review, public participation, license-amendment proceedings and any hearing rights are distinct from equipment refurbishment. Fuel-related approvals, operator training, staffing, emergency preparedness and coordination with PJM also have to be completed before commercial operation.
Where the NRC process stood on August 18, 2026
The NRC created a Crane Clean Energy Center Restart Panel to coordinate licensing, inspections and oversight. Its published schedule showed these milestones:
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Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →| Milestone | Status or date |
|---|---|
| Constellation environmental report | Submitted October 31, 2025 |
| NRC acceptance and schedule estimate | January 7, 2026 |
| Draft environmental assessment and draft finding of no significant impact | June 3, 2026 |
| Public-comment period | Scheduled to close July 8, 2026 |
| Final environmental assessment and finding of no significant impact | Projected for September 2026 on the NRC project page |
| Operating status as of August 18, 2026 | Not restarted; licensing restoration, inspections and upgrades remained in progress |
A draft environmental finding or an NRC review milestone is not the same as final authorization to generate electricity. The NRC’s 2026 notices and license-amendment notice provide the formal schedule and proceeding details.
Timeline from announcement to the 2027 target
- September 20, 2024: Constellation and Microsoft announce the 20-year PPA and proposed Unit 1 restart.
- May 13, 2025: The NRC approves the name change to the Christopher M. Crane Clean Energy Center.
- November 18, 2025: The Department of Energy closes a $1 billion loan for the project.
- June–September 2026: NRC environmental-review and public-comment milestones proceed.
- 2027: Constellation’s public target for return to service, contingent on approvals and restoration.
The 2027 date is a company target, not a guaranteed opening date. Constellation’s operating outlook is reported in its 2025 second-quarter results.
Cost, loan and financial exposure
Constellation has described an estimated restoration investment of approximately $1.6 billion. The DOE separately closed a $1 billion loan in November 2025. Those figures are not interchangeable: the loan is financing support, not the project’s total cost, and it is not a grant proving that taxpayers are paying the entire bill.
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The DOE says the loan is backed by Constellation’s credit and balance sheet. Its loan-closing announcement and Crane Restart project page describe the financing structure. Costs could change if inspections find additional work, equipment deliveries slip or regulators require further upgrades. The announced $1.6 billion estimate should therefore not be treated as a final, guaranteed outturn.
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Risks and unresolved questions
Regulatory and safety risk
The NRC must determine whether the restored licensing basis, systems, programs and components support safe operation. A filing, inspection or draft environmental document does not itself authorize restart.
Schedule risk
The 2027 target depends on environmental review, license amendments, inspections, component restoration, fuel-related approvals, operator readiness and grid coordination. Any one of those tracks can move the date.
Grid and market risk
Generation must be integrated into PJM’s transmission, capacity and energy markets. Interconnection rules, transmission constraints, transformer availability and market arrangements affect how the output is delivered and valued. Utility Dive describes additional PJM and delivery issues in its coverage of Constellation’s market plans.
Demand and contract risk
Microsoft’s data-center growth is an important commercial rationale, but AI workloads, construction timing, efficiency improvements and corporate clean-energy policies can change future electricity needs. The PPA improves revenue visibility without removing those uncertainties.
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Public-acceptance risk
The Three Mile Island name carries the history of the Unit 2 accident. Clear separation of Unit 1 from Unit 2 is essential to any safety discussion, and absolute claims that the site is simply “safe” should be left to the NRC’s regulatory findings.
Why this project matters beyond Microsoft
The DOE describes Crane as the second-ever restart in the United States of a nuclear reactor that had previously shut down for decommissioning. That makes it a test of whether retired plants can be restored when long-term buyers and financing are available, rather than replaced by entirely new reactors.
The outcome could influence how utilities, regulators and large electricity users evaluate other retired facilities. It could also show the limits of the strategy: a contract can improve economics, but it cannot bypass nuclear licensing, component qualification, grid rules or public scrutiny. Carnegie Endowment’s analysis of hyperscaler nuclear commitments is available at this assessment of the broader trend.
Bottom line
Three Mile Island is not fully “back” and Microsoft is not receiving a private transmission line from the island. Constellation is seeking to restore former Unit 1, now the Crane Clean Energy Center, and sell its approximately 835 MW of output under a 20-year PPA tied to the PJM grid. Commercial operation is targeted for 2027, but as of August 18, 2026 the reactor remained in the NRC’s licensing and restoration process.
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