In September 2024, Constellation Energy of Baltimore, MD, USA, owner and operator of the Three Mile Island (TMI) nuclear power plant near Middletown, PA, USA, announced that it would reopen the plant’s recently shuttered Unit 1 reactor to provide electricity for data centers owned by tech giant Microsoft (Redmond, WA, USA) [
1-
3]. The decision to restart the reactor—which surprised many people, including some nuclear scientists—reflects the surg-ing power demands of data centers, largely driven by the increas-ing use of artificial intelligence (AI) [
4],[
5]. Nuclear power, either from existing plants or from yet-to-be-built reactors, is one of the options that big tech companies like Microsoft, Amazon (Seattle, WA, USA), Meta (Menlo Park, CA, USA), and Google (Mountain View, CA, USA) are pursuing to meet these needs [
6].
Almost half a century ago, in March 1979, a cooling failure forced one of TMI’s two reactors to shut down [
7]. The accident led to a partial meltdown of the reactor, known as Unit 2, and it never produced power again. The catastrophe marked the begin-ning of a long decline in nuclear power use in the United States and many other countries. However, the other reactor at the site, the 835 MW Unit 1 (
Fig. 1), continued to generate electricity for 40 years before Constellation shut it down in 2019 [
1],[
2]. Even though the reactor still had 15 years on its operating license, it had become uneconomical to run [
2].
Although no shuttered nuclear plant has ever been restarted, experts do not expect any technical or regulatory difficulties in completing the necessary steps to get TMI’s Unit 1 up and running again. “Nothing I have seen says they cannot get it done,” said Todd Allen, professor of nuclear engineering and radiological sciences at the University of Michigan in Ann Arbor, MI, USA. Still, some experts question the wisdom of the move. Reopening TMI is “scraping the bottom of the barrel,” said Mark Jacobson, professor of civil and environmental engineering at Stanford University in Stanford, CA, USA. He said other sources of energy would be faster to bring online, better for the environment, and cheaper.
In just six years, the power needs of data centers have more than doubled, according to a 2024 report from the US Department of Energy’s Lawrence Berkeley National Laboratory in Berkeley, CA, USA [
8]. In 2018, the facilities consumed 1.9% of all electricity in the United States; by the end of 2023 that share had climbed to 4.4% [
8]. The report also forecasts that data center power usage would reach 12% of the US total by 2028. Sam Altman, the head of the ChatGPT-producing company OpenAI, has forecasted even higher power demands; in 2023, he predicted that some data cen-ters running AI models would soon require as much electricity as large cities [
9].
To provide much of this swelling demand for electricity, big tech companies are looking to new or existing fossil fuel-powered plants [
10]. But they have also committed to reaching net zero car-bon emissions within the next decade or two, and some states may limit their use of these more polluting sources [
11],[
12]. Thus, the companies are also making deals for renewables like solar and wind [
13]. And they see nuclear power as attractive because of its low carbon emissions and its ability to provide electricity around the clock [
11].
Data centers have already begun tapping power from operating nuclear plants. In early 2024 Amazon Web Services (AWS) bought a facility next to the 2.5 GW Susquehanna Steam Electric Station in Berwick, PA, USA [
14]. Although the nuclear plant is contracted to provide 300 MW directly to the data center, federal regulators refused AWS’s application to draw another 180 MW because it would harm the plant’s current customers [
14]. Tech companies are also considering siting data centers near nuclear power plants in other states [
14].
Two closed nuclear plants are now set to reopen, but the other one, the Palisades Nuclear Generating Station near South Haven, MI, USA, will not expressly produce electricity for a data center [
4]. Japan offers the closest parallel to these reopenings in the United States, said Michael Corradini, professor of nuclear engi-neering and nuclear physics at the University of Wisconsin in Madison, WI, USA. The accident at the Fukushima Daiichi plant in 2011 prompted Japan to take all its 54 reactors offline [
15]. After stress testing and safety upgrades, 13 had resumed operations as of late 2024 [
15],[
16]. The big difference, Corradini said, is that the process of decommissioning had not yet begun for the Japanese plants that eventually restarted.
In contrast, TMI’s Unit 1 had entered a decommissioning pro-cess known as SAFSTOR (short for “safe storage”), in which the facility sits idle to allow levels of radioactivity to decline, making its eventual disassembly easier [
17]. The fuel was removed, most of its 675 employees were laid off or transferred [
3], and the Nuclear Regulatory Commission (NRC), the US federal agency that oversees nuclear power, withdrew the plant’s operating license (the same changes occurred at the Palisades plant, which was also in SAFSTOR). Because dismantling had not begun and the shutdown occurred recently, “the plant is still in good condition,” said Jacopo Buongiorno, professor of nuclear science and engineer-ing at the Massachusetts Institute of Technology in Cambridge, MA, USA.
Restarting the reactors will, however, require careful inspec-tions of all components of the plants to ensure their safe operation [
18]. Constellation has already announced that it will replace Unit 1’s main transformer, which will cost 100 million USD; other equipment may need to be swapped out as well [
19]. Because the staff was slashed in 2019, Constellation will need to hire not just nuclear engineers, but also welders, machinists, electricians, and other employees, said Buongiorno. “One of the biggest chal-lenges will be to have enough people to run the plant,” he said. He added that the company will also have to train the plant oper-ators, either at its other nuclear reactors or with a simulator of TMI’s control room. Obtaining the enriched uranium fuel for the plant could also be a bottleneck, said Corradini. The world’s supply—much of which comes from Russia—is tight, although the United States is pursuing domestic sources [
20].
If the NRC determines that the plant can run safely and that the staff is properly trained, it will restore Unit 1’s operating license. Constellation’s schedule calls for the plant—branded with a new name, the Crane Clean Energy Center—to start delivering electricity in 2028 [
21]. The cost of reopening the plant is unclear, but Con-stellation has applied for a 1.6 billion USD loan guarantee from the US government, a common practice in the nuclear industry to reduce the risk of investments by making taxpayers liable should the capital-intensive ventures fail [
22].
If TMI resumes producing electricity, it will be “a win-win for everyone,” said Buongiorno. But Jacobson calls the plan to reopen the plant wrongheaded. New solar, wind, or even advanced geothermal generating facilities [
23] could be up and running in two to three years and would provide electricity at lower cost and with a smaller carbon footprint, Jacobson said.
“There is ample room for both nuclear and renewables,” coun-tered Buongiorno. “The US alone will need close to 50 GW of new electricity to power data centers,” he said. “The sad reality is that most of that new capacity will be covered by natural gas, with lots of emissions.”
Experts say that TMI’s revival will not start a trend, with only one other shuttered nuclear power plant in the United States, the Duane Arnold Energy Center near Cedar Rapids, IA, a viable candi-date to return to service [
18]. The other closed nuclear power plants are too far into the decommissioning process for reopening to be an option. As of 2017, 10 plants had completed decommis-sioning and another 20 were in various stages of decommissioning [
24]. “Do not expect two dozen reactors to come back online. We may build others, but that is a different issue,” said Buongiorno.
Constructing new full-sized nuclear power plants is expensive andtime-consuming.CompletedinApril2024,thelasttworeactors to open in the United States, the Vogtle 3 and Vogtle 4 units in Georgia, were delivered seven years late and cost 35 billion USD, a price more than double the initial estimates [
25]. Still, said Allen, the lessons from building these reactors could help speed construc-tion and cut the costs of similar future projects. The ravenous demands of data centers for power may change the cost-benefit calculationsaswell.”Itseemsmuchmorelikelynowthatwewould consider a big plant than three or four years ago,” Allen said.
As a less daunting alternative, some tech companies are betting on scaled-down nuclear alternatives known as small modular reac-tors (SMRs), which would provide less than one-third the power of a conventional nuclear plant with a much smaller price tag [
26]. Google has signed an agreement to buy electricity from Kairos Power of Alameda, CA, USA, which plans to deploy its first SMR in 2030 [
27]. Amazon and Oracle (Austin, TX, USA) also have plans to obtain power from small reactors [
28],[
29]. However, no company has yet built one of these reactors and shown that it will work. In any case, it appears that big tech’s newly voracious appetite for electricity provides some cause for optimism about a reboot for the nuclear industry, including efforts to develop fusion-based power [
30].
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