A visit to Three Mile Island, where Constellation Energy hopes to restart a nuclear power plant

Constellation Energy has applied to reopen a nuclear power plant on Three Mile Island in the Susquehanna — not the one shut after a coolant failure in 1979, but its long-running neighbor, closed by Exelon Corp. in 2019 , as cheaper natural gas made the aging uranium plant too expensive to run.

Constellation, a Baltimore-based electric plant operator spun off by public-utility giant Exelon in 2022, says it wants to bring the plant back by 2028, pending federal approvals , to take advantage of recent U.S. tax credits for non-carbon-generated electricity and to meet demand from Microsoft.

The software giant agreed to buy power from Constellation equal to the plant's full 835 megawatts — enough to power all 800,000 homes in Philadelphia — for 20 years after the plant's reopening, to run its growing network of data centers .

Constellation has been inviting public officials, media, energy scholars, and others for limited tours of its mothballed nuclear plant near Middletown, Pa., south of Harrisburg. The company has rechristened the plant as Crane Clean Energy Center after Exelon's late chief executive and nuclear-power advocate Christopher M. Crane, who died in April at 65.

The project would require thousands of building-trades workers to do maintenance, replacement, and upgrades over the next three years. Constellation said it would employ 730 employees when it reopened.

Constellation has been marketing the Crane facility as part of the company's 5,200-megawatt "clean energy corridor" of water- and nuclear-powered, nonfossil fuel-burning electric plants in southern Pennsylvania.

The plant's best known feature is its 372-foot-tall reinforced concrete cooling tower used to dissipate heat as plant water is returned to the river. It stands out in a region where Amish farms and hills covered with second-growth red-oak woods, parks, and hiking trails alternate with post-World-War II factories, including GlaxoSmithKline's new drug production center in nearby Marietta.

The Constellation site is secure as a prison. Officials warned visitors away from the razor wire; rifle-carrying, body-armor-wearing guards; and other security measures. They redirected attention to the high-roofed building where steam heated by uranium fission would once again turn turbines around the clock to generate power.

Visitors accustomed to digital controls and wireless systems ubiquitous in today's industrial settings immediately noticed the analog controls, some of them based on designs dating to the plant's construction in the 1970s.

Craig Smith, a veteran Exelon nuclear-plant operator who has been training new operators for Constellation, acted as a tour guide and fielded questions about the analog controls, some based on designs dating to the plant's construction in the 1970s. He said the dated systems — so different from newer industrial plants' digital controls and wireless systems — have been well-maintained and tested. There are no current plans to install digital technology, though some is being added at the company's larger nuclear complex in Limerick, Montgomery County .

Because the Three Mile Island plant was active until 2019, the company says most of its nuclear and electrical equipment and water and steam loops can be used, after more testing, with routine maintenance.

An exception: Copper in the transformer complex is pitted, and the two main transformers that regulate power to commercial levels as it leaves the plant will have to be replaced, at an expected cost of around $100 million, mostly for construction and installation, Constellation says.

Constellation is recruiting federally certified operators for the complex. Five would work in the control room on each 12-hour shift at the nuclear plant, which observes very different routines from those operating traditional carbon-fueled plants. Constellation officials say they have already attracted hundreds of applicants, including both power plant veterans and recent college and trade school grads. The positions pay over $100,000 a year. A first batch of 150 operators is already enrolled in an 18-month training course.

Many of the parts at the Crane plant were made by General Electric and other U.S. manufacturers, some of whom have quit or downscaled their nuclear plant service work as new reactor orders stalled in the 1980s.

The Biden administration has favored nuclear power as a relatively clean, reliable source of energy that doesn't burn carbon, despite the lack of a long-term solution for storing radioactive spent uranium, which takes thousands of years to decay. All of the plant's spent fuel since its opening is stored in steel and concrete in a space the company says is about the size of a tennis court near the southern end of Three Mile Island.