Microsoft’s deal to restart the Three Mile Island reactor just cleared a key federal hurdle

The plan to revive a reactor at Three Mile Island under a landmark power deal with Microsoft has cleared a series of federal milestones during 2026, moving the long-idled Pennsylvania plant closer to a targeted return to service in 2027. The reactor, formerly known as Three Mile Island Unit 1 and now rebranded the Crane Clean Energy Center, was retired in 2019 for economic reasons and is being restored by its owner, Constellation Energy, to supply electricity for the technology company’s growing computing needs. Final federal sign-off on operations has not yet been granted, but the restart has advanced through several regulatory checkpoints that once loomed as major obstacles.

The deal that set the restart in motion

Constellation announced in 2024 that it would restart the reactor under a 20-year power purchase agreement with Microsoft, its largest-ever such deal, with the software company committing to buy the plant’s output to help power its data centers. The arrangement turned a decommissioned generating unit into the centerpiece of a broader push to use nuclear energy for the electricity-hungry digital economy, and it helped spark wider commercial interest in reviving retired reactors.

The reactor sits adjacent to Three Mile Island Unit 2, the reactor that suffered a partial meltdown in 1979 and has been undergoing decommissioning ever since. Constellation has stressed that Unit 1 is a fully independent facility whose long-term operation was unaffected by the 1979 accident, and that it was shut down years later purely because it had become uneconomic to run.

What restarting a reactor requires

Bringing a retired reactor back online is not a matter of simply flipping a switch. It requires approval from the Nuclear Regulatory Commission following a comprehensive safety and environmental review, along with permits from state and local agencies. Constellation is pursuing a license to extend operations to at least 2054 and has said it expects the plant to be ready for service in 2027 after a significant investment to restore its safety and operating systems. The Nuclear Regulatory Commission maintains a public record for the Crane Clean Energy Center tracking the reviews tied to the restart.

The federal review has multiple components, each of which must be satisfied before the reactor can generate power again. Regulators examine the physical condition of the plant, the adequacy of its safety systems, the qualifications of its operators and the environmental consequences of returning it to service, a process that unfolds over many months.

The federal checkpoints cleared in 2026

Over the course of 2026, the restart passed through several of those checkpoints. In June, the Federal Energy Regulatory Commission granted a waiver from certain grid-market rules that had posed a barrier to the plant’s reconnection, an approval that removed one of the near-term hurdles to the 2027 timeline. Separately, the Nuclear Regulatory Commission acted on the company’s request regarding the use of new nuclear fuel at the facility, and the agency’s environmental review concluded that restarting the reactor would have no significant environmental impacts.

Those steps do not amount to final permission to operate, which remains pending, but together they represent meaningful progress through the regulatory gauntlet. Each approval narrows the list of outstanding requirements and reinforces the company’s stated schedule, even as the most consequential decision, final operating approval, still lies ahead.

What the plant is expected to deliver

Constellation has laid out the stakes of the revival in concrete terms. The restored center is expected to restore 835 megawatts of carbon-free electricity to the grid, create roughly 3,400 direct and indirect jobs, and deliver an estimated $3.6 billion in state and federal tax revenue while adding about $16 billion to Pennsylvania’s economy. The company also projects that the plant will avoid the release of some 61 million tons of carbon dioxide over 20 years compared with fossil-fueled generation.

According to Constellation’s own description of the project, physical work has been progressing ahead of schedule, including the delivery of major equipment such as a replacement transformer to the site. The company has framed the restart as a defining moment for the U.S. nuclear industry and a template for using existing reactors to meet surging power demand.

A test case for reviving retired nuclear plants

The Three Mile Island revival has become a closely watched example of a broader trend in which technology companies, hungry for reliable, low-carbon electricity to run data centers, are turning to nuclear power. Constellation’s deal was among the first to pair a specific retired reactor with a single large corporate buyer, and its progress is being scrutinized as a signal of whether such restarts can be executed on time and on budget.

Federal officials have publicly embraced the effort, with the site drawing visits from senior energy officials who have cast the restart as part of a national push for domestic energy production. That political support has coincided with the regulatory approvals, though the technical and licensing work remains the decisive factor in whether the plant meets its 2027 goal.

What remains before the reactor can run

Despite the milestones cleared so far, the reactor cannot generate electricity until the Nuclear Regulatory Commission grants final approval to return it to operation, and the plant must also complete the physical restoration of its systems. Constellation has said it is positioned to begin producing electricity by late 2027 if the remaining approvals are granted, and the facility has been preparing to receive nuclear material to be held in storage until operations are authorized. For now, the restart stands as an advanced but not yet completed project, one that has moved through key federal gates while awaiting the final clearance that would allow a reactor idled since 2019 to power the grid once more.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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