The nuclear reactor at what is now called the Crane Clean Energy Center, better known by its old name of Three Mile Island, has cleared a major grid-approval step on its path back to service, moving its restart timeline up by roughly a year. The facility, idle since 2019, is being brought back specifically to supply power to Microsoft’s data centers under a long-term agreement signed in 2024.
From Shutdown Reactor To A Microsoft Power Source
Unit 1 at the Pennsylvania site was shut down in 2019 for economic reasons, unable to compete with cheaper natural gas and renewable power at the time, and it sat idle even as its sister reactor, Unit 2, remained the site of the 1979 partial meltdown that gave Three Mile Island its notoriety. Plant owner Constellation Energy rebranded the surviving reactor the Crane Clean Energy Center and struck a 20-year power purchase agreement with Microsoft, tying the reactor’s revival directly to the technology company’s growing electricity needs for artificial intelligence and cloud computing.
That arrangement reflects a broader shift among large technology companies toward locking in dedicated power sources rather than competing for capacity on an already strained grid, since data centers running AI workloads draw far more continuous power than typical commercial buildings.
The Microsoft agreement runs for 20 years and covers the full output of the restarted unit, giving Constellation a guaranteed buyer for decades of electricity from a reactor that had been sitting idle and generating no revenue at all. That kind of long-term commitment is what typically makes a restart of this scale financially workable, since the utility can plan recertification and staffing costs against a revenue stream that is already locked in rather than betting on future market prices for electricity.
The Grid Approval That Had Been Missing
Restarting a shuttered nuclear plant requires more than mechanical readiness; it also requires the regional grid operator to approve how and when the reactor’s output gets connected back into the transmission system. Grid operator PJM Interconnection approved an early interconnection request for the reactor, according to industry reporting on the project’s progress, clearing a procedural bottleneck that had been one of the last major steps standing between the plant and an active grid connection.
Interconnection approval matters because a reactor cannot legally deliver power onto a shared grid without it, regardless of how close the plant itself is to being ready, making this kind of regulatory sign-off as consequential to a restart timeline as any physical repair work.
A Restart Timeline Pulled Forward By A Year
Constellation had originally targeted 2028 for the reactor’s return to service, but the company has said the newly secured grid approval and faster-than-expected progress on equipment inspections allow it to aim for 2027 instead. Speeding up a nuclear restart by a full year is unusual in an industry where regulatory reviews and equipment recertification typically move slowly and conservatively.
The project has also drawn federal backing, with the U.S. Department of Energy supporting the restart through a loan guarantee, underscoring how the federal government has started treating existing, licensed nuclear capacity as a faster route to new electricity supply than building reactors from scratch.
That federal support matters because financing has historically been one of the biggest obstacles to nuclear projects, given how much capital a reactor requires before it produces its first kilowatt-hour of billable power. A loan guarantee lowers the effective cost of that financing, making an aging reactor’s return to service look more attractive relative to newer, unproven reactor designs that still carry years of licensing risk.
Why Restarting Beats Building New
Nuclear plants like the Crane Clean Energy Center already hold a federal operating history, existing transmission connections and trained local workforces, advantages that let a restart move years faster than permitting and constructing a brand-new reactor. That speed is central to why Microsoft chose to fund a restart rather than wait for a new small modular reactor design to clear licensing, since newer reactor technologies still face years of regulatory review before they can generate a single watt for a customer.
Existing reactors also carry a structural advantage once running: nuclear plants post the highest capacity factor of any power source, generating at or near full output more consistently than gas, wind or solar, which is precisely the steady baseline load that data center operators want locked in for a facility expected to run around the clock.
What Still Has To Happen Before Power Flows Again
Clearing the grid-interconnection hurdle does not mean the reactor is ready to generate electricity immediately. Constellation still has to complete equipment recertification, refuel the reactor core, retrain and rehire plant staff to federal licensing standards, and pass inspections from the Nuclear Regulatory Commission before Unit 1 can legally return to service. Each of those steps carries its own schedule risk, which is why utilities tend to treat an accelerated timeline as a target rather than a guarantee until the reactor is actually generating power.
If the 2027 timeline holds, the Crane Clean Energy Center would become one of the first shuttered U.S. nuclear reactors brought back into commercial service, a precedent other utilities sitting on idle nuclear capacity are already watching closely as they weigh similar restarts of their own.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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