NRC Completes Environmental Review for Three Mile Island Unit 1 Restart

The US Nuclear Regulatory Commission has completed its environmental review of Constellation Energy’s plan to restart Unit 1 of the Christopher M. Crane Clean Energy Center in Pennsylvania, formerly Three Mile Island, issuing a final environmental assessment and a finding of no significant impact on September 25, 2026. The determination, made jointly with the Department of Energy’s Office of Energy Dominance Financing, clears one of the last major regulatory hurdles before the 835 MW reactor can return to service, which Constellation has targeted for 2027.

What the finding actually covers

A finding of no significant impact, or FONSI, is not a license and does not by itself authorize the reactor to restart. It is the NRC’s conclusion, after reviewing environmental factors such as water use, radiological releases and impacts on surrounding communities, that reauthorizing power operations at the plant does not require a more extensive environmental impact statement. The NRC released a draft version of the assessment for public comment on June 8, 2026, with the comment window closing a month later; the final version issued in September incorporates the agency’s responses to that input. Separate safety and licensing reviews, which examine the physical condition of the plant after more than six years in a shut-down state, continue on their own track toward a restart decision.

A different reactor from the one associated with 1979

The facility is frequently shorthanded as “Three Mile Island,” which can blur an important distinction: the 1979 partial meltdown occurred at the site’s Unit 2, a separate reactor that was permanently shut down and has remained in long-term decommissioning ever since. Unit 1, the reactor now under review, continued operating for another four decades without incident and was retired in September 2019 for economic reasons, not safety ones, when its owner at the time could not secure a state subsidy to keep it running as a merchant plant in a low-price power market. Constellation, which inherited the site through its 2022 merger of Exelon’s generation business, renamed the facility after former Exelon chief executive Christopher Crane in 2024 as part of the restart announcement.

The deal that revived a retired reactor

The restart is tied to a 20-year power purchase agreement Constellation signed with Microsoft in September 2024, under which Microsoft will buy the plant’s output to help offset the electricity its data centers draw from the PJM grid, the wholesale market spanning Pennsylvania and twelve other Mid-Atlantic and Midwest states. The arrangement was among the first of a wave of tech-sector nuclear deals aimed at securing carbon-free, round-the-clock power for AI and cloud computing infrastructure, a trend that has since drawn other hyperscalers into similar agreements with plant operators and reactor developers. FERC’s rejection of a separate bid by Oklo to jump PJM’s interconnection queue in Virginia earlier this year underscored how contested grid access has become in the same territory Crane will feed once it restarts.

Economic case and public pushback

An economic impact analysis commissioned around the restart announcement projected that returning the plant to service would create 3,400 direct and indirect jobs and add roughly $16 billion to Pennsylvania’s economy over the plant’s operating life, along with more than $3 billion in state and federal tax revenue. Public comments gathered during the NRC’s review reflected a split reaction: supporters pointed to those employment and tax figures along with the carbon-free generation the plant would add to a grid under growing strain from data-center load, while opponents raised concerns about emergency preparedness in the surrounding area should problems arise at a reactor that has been offline since 2019. The NRC’s environmental finding addresses the former set of considerations; it does not resolve the separate safety case, which will be decided through the agency’s ongoing licensing review.

Part of a broader restart push

Crane’s case is one of several US efforts to bring recently shuttered reactors back into service rather than build new capacity from scratch, a route regulators and developers see as faster than new construction even though it still requires extensive inspection and recertification work. The push has coincided with a run of announcements tying nuclear plants and new reactor projects directly to specific corporate power buyers, including Samsung C&T’s investment in Kairos Power’s Hermes 2 project, even as other developers have run into trouble: Bechtel’s exit from TerraPower’s Natrium reactor construction in Wyoming this month was a reminder that the sector’s ambitions still outrun its execution record in places. Crane’s restart, by contrast, involves a reactor with an established operating history rather than a first-of-a-kind design, which is part of why Constellation and Microsoft structured their deal around it in the first place.

What comes next

With the environmental review complete, the restart timeline now depends on the NRC’s parallel safety and licensing evaluation, along with Constellation’s own inspection, testing and staffing work at the site. Constellation has said it is targeting 2027 for the reactor’s return to the grid, a date the company has previously described as ahead of its original schedule; the company employed roughly 600 people at the site as of its 2024 announcement and has said staffing would grow toward historical operating levels as the restart approaches. The Crane case is likely to be watched closely as a template for other utilities weighing whether to bring their own recently retired reactors back online.

Sources

• World Nuclear News, “NRC completes environmental review of Crane restart,” September 28, 2026 — FONSI issuance date, joint DOE role, timeline of draft EA and public comment period. world-nuclear-news.org
• Federal Register, “Constellation Energy Generation, LLC; Christopher M. Crane Clean Energy Center; Environmental Assessment and Finding of No Significant Impact,” September 25, 2026 — official NRC/DOE notice and FONSI date. federalregister.gov
• Constellation Energy, “Constellation to Launch Crane Clean Energy Center, Restoring Jobs and Carbon-Free Power to The Grid,” September 2024 — Microsoft PPA terms, plant capacity, economic impact study figures, renaming of the facility. constellationenergy.com
• Pennsylvania Capital-Star, “Concern persists as former Three Mile Island nuclear plant progresses toward 2027 restart” — public comment sentiment, community concerns. penncapital-star.com

Illustrative image. Photo: Nuclear Regulatory Commission, Public domain, via Wikimedia Commons — source