what it will take to reopen Three Mile Island safely

Microsoft announced on 20 September that it had struck a 20-year deal to purchase energy from a dormant nuclear power plant that will be brought back online. And not just any plant: Three Mile Island, the facility in Londonderry Township, Pennsylvania, that was the site of the worst-ever nuclear accident on US soil when a partial meltdown of one of its reactors occurred in 1979.

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The move, which symbolizes technology giants’ need to power their growing artificial-intelligence (AI) efforts, raises questions over how shuttered nuclear plants can be restarted safely — not least because Three Mile Island isn’t the only plant being brought out of retirement.

Palisades Nuclear Plant, an 805-megawatt facility in Covert, Michigan, was shut down in May 2022. But the energy company that owns it, Holtec International, based in Jupiter, Florida, plans to reopen it. This reversal in the facility’s fortunes has been bolstered by a US$1.5-billion conditional loan commitment from the US Department of Energy (DoE), which sees nuclear plants — a source of low-carbon electricity — as a way of helping the country to meet its ambitious climate goals. The Palisades plant is on track to reopen in late 2025.

“It’s the first time something like this has been attempted, that we’re aware of, worldwide,” says Jason Kozal, director of the reactor safety division at a regional office of the US Nuclear Regulatory Commission (NRC) in Naperville, Illinois, and the co-chair of a regulatory panel overseeing the restart of Palisades.

Here, Nature talks to nuclear specialists about what it will take to restart these plants and whether more are on the way as the world’s demand for AI grows.

A change in fortunes

Since 2012, more than a dozen nuclear plants have been shut down in the United States, in some cases as a result of unfavourable economics. Less cost-effective plants — such as those with only a single working reactor — struggled to remain profitable in states with deregulated electricity markets and widely varying prices. Three Mile Island, owned by the utility company Constellation Energy in Baltimore, Maryland, is a prime example. Today, 54 US plants remain in operation, running a total of 94 reactors.

Nuclear energy, which accounts for about 9% of the world’s electricity, has seen some resurgence internationally, but is also competing with other energy sources, including renewables. After the 2011 Fukushima Daiichi disaster, Japan suspended operations at all of its 48 remaining nuclear plants, but these are gradually being brought back online, in part to cut dependence on gas imports. By contrast, Germany announced a phase-out of its nuclear plants in 2011, and shut down its last three in 2023.

In the United States, nuclear energy’s fortunes might be turning as technology companies race to build enormous, energy-gobbling data centres to support their AI systems and other applications while somehow fulfilling their climate pledges. Microsoft, for instance, has committed to being carbon negative by 2030.

“It’s further confirmation of the value of nuclear, and, if the deal is right — if the price is right — then it makes business sense, as well,” says Jacopo Buongiorno, the director of the Center for Advanced Nuclear Energy Systems at the Massachusetts Institute of Technology in Cambridge.

A new start

This isn’t the first time that the United States has brought a powered-down reactor back online. In 1985, for example, the Tennessee Valley Authority, a federally owned electric utility company, took the reactors at its Browns Ferry Nuclear Power Plant in Athens, Alabama, offline. After years of refurbishment, they were brought back online, with the final reactor restarted in 2007.

The cases of Palisades and Three Mile Island are different, however. When those plants closed, their then-owners made legal statements that the facilities would be shut down, even though their operating licenses were still active. Three Mile Island, which will be renamed the Crane Clean Energy Center under the proposed restart, shut down its single remaining functional reactor in 2019.

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Because the plants were slated for shutdown and safety checks were therefore stopped, regulators and companies must now navigate a complex licensing, oversight and environmental-assessment process to reverse the plants’ decommissioning.

Safety checks will be needed to ensure, among other things, that the plants can operate securely once uranium fuel rods have been replaced in their reactors. When these plants were decommissioned, their radioactive fuel was removed and stored, so the facilities no longer needed to adhere to many exacting technical specifications, says Jamie Pelton, also a co-chair of the Palisades restart panel, and a deputy director at the NRC’s Office of Nuclear Reactor Regulation in Rockville, Maryland.

It will be no small feat to reinstate those safety regulations: to meet the standards, infrastructure will need to be inspected carefully. According to Buongiorno, any metallic components in the plants that have corroded since the shutdowns, including wires and cables used in instrumentation and controls, will need to be replaced.

The plants’ turbine generators, which make electricity from the steam produced as the plants’ fuel rods heat up water, will also get a close look. After sitting dormant for years, a turbine could develop defects within its shaft or corrosion along its blades that would require refurbishment. In the case of Palisades, the NRC announced on 18 September that the plant’s steam generators would need further testing and repair, following inspections conducted by Holtec.

Nuclear’s prospects

As the plants near their restart dates, their operators will also have to contend with a challenge faced by even fully operational plants: the need to source fresh nuclear fuel. US nuclear utility companies have long counted on the international market to buy much of the necessary raw yellowcake uranium and the services that separate and enrich uranium-235, the isotope used in nuclear reactors’ fuel rods. Russia has been a major international supplier of these services, even after the country’s 2022 invasion of Ukraine, because US and European sanctions have not targeted nuclear fuel. But to minimize its reliance on Russia, the United States is building up its own supply chain, with the DoE offering $3.4 billion to buy domestically enriched uranium.

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There probably won’t be too many other restarts of mothballed nuclear plants in the United States, however, even as demand for low-carbon electricity grows. Not every US plant that has been shut down is necessarily in good enough condition to be easily refurbished — and the idea of reopening some of those would meet with too much resistance. As an example, Buongiorno points to New York’s Indian Point Energy Center, which was closed in 2021. The plant’s proximity to New York City had long provoked criticism from nuclear-safety advocates.

But that doesn’t mean that all of these sites will remain unused. One option is to build advanced reactors — including large reactors with upgraded safety features and small modular reactors with innovative designs — on sites where old nuclear plants once stood, to take advantage of existing transmission lines and infrastructure. “We might see interest in the US in building more of these large reactors, whether that’s fuelled by data centres or some other applications,” Buongiorno adds. “Utilities and customers are exploring this at the moment.”