Nuclear power is experiencing a major resurgence as artificial intelligence data centers consume unprecedented amounts of electricity, forcing tech companies and energy experts to reconsider the role of atomic energy in powering the grid. Microsoft recently signed a 20-year agreement to purchase power from Three Mile Island Unit 1 in Pennsylvania, which will be restarted as the Crane Clean Energy Center and could generate enough energy annually to power approximately 700,000 homes. Meanwhile, Constellation Energy, the largest U.S. producer of carbon-free nuclear power, has become central to data center power demand and is attracting significant investor attention as technology companies seek reliable electricity sources.

What's Driving the Nuclear Revival?

The explosion in AI computing power has created an urgent energy problem. Data centers running large language models and training artificial intelligence systems consume enormous amounts of electricity around the clock. Unlike traditional computing workloads that fluctuate throughout the day, AI infrastructure requires constant, reliable power. This demand has forced technology companies to look beyond conventional renewable energy sources and toward nuclear plants that can provide steady, carbon-free electricity without interruption.

Constellation Energy has capitalized on this shift by signing long-term power agreements with major technology customers, including its Microsoft deal linked to Three Mile Island's restart. The company operates the largest fleet of nuclear power plants in the United States and has expanded its generation portfolio through the acquisition of Calpine, positioning itself as a key supplier for data center operators seeking reliable power.

Why Can't Renewables Alone Power AI Data Centers?

While wind and solar energy have become dramatically cheaper and more widespread, they face fundamental limitations that make them unsuitable as the sole power source for data centers. According to Elmer Lewis, a professor emeritus of mechanical engineering at Northwestern University who has studied nuclear systems for more than six decades, renewable energy sources have three major drawbacks that undercut their benefits.

Lewis examined these challenges in detail in his new book "Renewables or Nuclear: Which Should Lead in Curbing Climate Change?" published in 2026. He explained that the limitations of wind and solar power create significant obstacles for grid stability and energy reliability.

• Intermittency: The sun does not always shine, and the wind does not always blow. During periods when renewable sources are not generating power, other electricity sources or stored energy must step in to meet demand and keep the grid stable.
• Land Requirements: Wind and solar are dilute energy sources requiring vast amounts of land. To generate the same electricity as two nuclear reactors serving the Chicago area using wind power alone would require a wind farm covering an area roughly the size of Cook County, which includes much of the Chicago metropolitan area.
• Grid Stability and Transmission: The best wind resources are often located far from major population centers, requiring extensive transmission infrastructure to carry electricity to cities where people use it. Building new transmission lines across multiple states involves complex approval processes and significant delays.

The most challenging problem is what experts call the "dark doldrums," periods lasting days or even weeks when skies are overcast and winds are weak. Current large battery installations generally provide only hours of storage, not the days or weeks needed to bridge extended periods of low renewable generation. Research into long-duration energy storage has been disappointing, with no clear path toward a foreseeable solution.

"If we try to get a larger percentage of electricity from renewables, their limitations will become more apparent. Because of intermittency, land use, and grid stability issues, I think the proportion of nuclear will increase," said Elmer Lewis.

Elmer Lewis, Professor Emeritus of Mechanical Engineering at Northwestern University

How Have Nuclear Safety Improvements Changed the Industry?

Public concerns about nuclear safety have historically hindered the industry's growth, but recent advances in reactor design have addressed the lessons learned from past accidents. Lewis noted that major nuclear incidents, including Chernobyl and Fukushima, have directly influenced the development of safer reactor designs.

Fukushima provided particularly important lessons about emergency cooling systems. When the earthquake hit, reactors shut down automatically, but radioactive decay continues producing heat even after shutdown. The tsunami flooded the diesel generators powering emergency cooling systems, eventually causing the heat to escape the reactors. Modern reactor designs have incorporated solutions to prevent this scenario.

Newer nuclear plants use natural convection to remove decay heat, a passive safety feature that requires no electrically powered pumps or external power sources. Hot water rises and cooler water falls, creating circulation automatically. This means that even if outside electricity is lost, heat continues to be removed from the reactor. Additionally, modern reactors feature improved containment structures, thick reinforced barriers that prevent radioactive material from escaping into the environment in the event of an accident.

What Obstacles Still Face Nuclear Expansion?

Despite the renewed interest in nuclear power, significant challenges remain. The United States experienced a long period of stagnation in nuclear reactor construction, during which the workforce and supply chain that once supported reactor development largely disappeared. When construction resumed, projects suffered substantial delays and major cost overruns, making nuclear power more expensive than it was historically.

Public opinion continues to influence nuclear policy, though Lewis argues that safety concerns should be considered in context with other risks. Fossil fuel air pollution causes thousands of deaths annually, while modern nuclear plants have multiple safety systems preventing catastrophic failures. The industry must balance these competing concerns as it seeks to expand capacity to meet AI data center demand.

Constellation Energy's stock performance reflects investor confidence in nuclear's role in powering AI infrastructure, though the company faces risks including changes in demand, competitive pressure, regulatory developments, and shifts in the broader economic environment. The ability to execute on strategic priorities and manage costs in an uncertain market will influence results.

How to Evaluate Nuclear Power's Role in Your Region's Energy Future

• Track Data Center Power Agreements: Monitor announcements of new long-term power contracts between technology companies and nuclear operators, as these signal future demand and investment in nuclear infrastructure expansion.
• Follow Nuclear Policy Developments: Watch for federal and state legislation supporting nuclear power, including relicensing decisions for existing plants and permits for new reactor construction, as policy support directly influences industry growth.
• Monitor Capacity and Output Metrics: Pay attention to nuclear plant uprates, capacity factors, and relicensing approvals, which indicate whether existing reactors can increase power generation to meet growing AI data center demand.
• Assess Renewable Integration Plans: Examine how regional grid operators plan to balance nuclear baseload power with renewable energy sources and battery storage, as this determines the realistic mix of energy sources for reliable electricity supply.

The convergence of AI's explosive growth and nuclear power's resurgence represents a fundamental shift in how the technology industry approaches energy infrastructure. As electricity demand from data centers continues to rise, the debate between renewables and nuclear is no longer theoretical; it is shaping real investment decisions and infrastructure development across the United States.

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