FROM ITS HUMBLE start as a glacial trickle in the Swiss Alps, the Rhône River quickly transforms into one of the world’s most industrialized waterways. As it winds through the south of France toward the Mediterranean Sea, its chilly water is drawn into boilers, sucked through pipes as coolant, deviated for agriculture. Among its biggest customers is a battalion of nuclear reactors. Since the 1970s, the river and its tributaries have helped generate about a quarter of France’s atomic energy.
But in recent weeks that hasn’t been the case. Amidst a slow-burning heat wave that has killed hundreds and sparked intense wildfires across Western Europe, and combined with already low water levels due to drought, the Rhône’s water has gotten too hot for the job. It’s no longer possible to cool reactors without expelling water downstream that’s so hot as to extinguish aquatic life. So a few weeks ago, Électricité de France (EDF) began powering down some reactors along the Rhône and a second major river in the south, the Garonne. That’s by now a familiar story: Similar shutdowns due to drought and heat occurred in 2018 and 2019. This summer’s cuts, combined with malfunctions and maintenance on other reactors, have helped reduce France’s nuclear power output by nearly 50 percent.
Of all the low-carbon energy sources that will likely be necessary to fight climate change, nuclear power is usually thought of as the least perturbable. It’s the reinforcement that’s called in when the weather doesn’t cooperate for other zero-carbon energy sources, like wind and solar. But the nuclear industry faces its own climate risks.
Problems with water—too much of it or too little—are more commonly associated with hydroelectric dams, which have struggled to maintain output in drying places like the American West. But as the Swedish historian Per Högselius puts it, much of present-day nuclear engineering is not about splitting atoms, but about managing larger-scale aquatic concerns. Nuclear technicians are known to refer to their craft as a very complicated way of boiling water, producing steam that spins turbines. But much more is usually required to keep the reactor cool. That’s why so many facilities are located by the sea and along big rivers like the Rhône.
Plenty of other industries are affected by hotter rivers, including big factories and power plants that run on coal and gas. But nuclear plants are unique because of their immense size and the central role they play in keeping energy grids online in places like France. And warming and dwindling rivers are not the only climate challenges they face. On the coasts, a combination of sea level rise and more frequent and intense storms means heightened flooding risks. Scientists have also pointed to other, more unusual challenges, like more frequent algal blooms and exploding jellyfish populations, which can clog up the water pipes.
Nuclear plants are also built to last well into the future, with lifespans that extend a half-century or more. Many were constructed in the 1970s and '80s—long before regulators thought to factor in climate-related threats they would eventually encounter, explains Natalie Kopytko, a researcher at the University of Leeds who has dug into nuclear regulatory frameworks to look for climate considerations. “I saw absolutely nothing about climate change, which was quite scary,” she says. Where Kopytko did see the climate invoked, the plans assumed that current weather patterns would hold well into the future.
Some of the current concerns about climate change are related to safety—and the sector has started making some moves to address them. After the Fukushima disaster in Japan, caused by the Tohoku earthquake and tsunami in 2011, the US Nuclear Regulatory Commission (NRC) began drafting new rules to harden existing plants to climate threats, such as storms and sea level rise. The process identified dozens of facilities that could face flooding problems under extreme conditions. But in 2019 those plans were largely scuttled by the Republican-led leadership, who argued the costs were too high for the nuclear industry to adopt for such low-probability events. (“This decision is nonsensical,” Democrat-appointed commissioner Jeff Baran wrote in a dissent at the time.)
The nuclear industry and environmental groups continue to disagree on whether existing regulations capture the latest science, particularly on the topic of sea level rise. “There’s a lot of margin on the safety side for nuclear plants,” says Doug True, chief nuclear officer of the Nuclear Energy Institute, a US-based industry group, adding that utilities regularly update their models on climate risks and have already undertaken extensive steps to protect their facilities from extreme weather.
But those climate threats are once again being discussed more openly as regulators in Europe and the US consider extending the lives of nuclear plants in order to fight climate change. In 2019, the NRC began approving 20-year extensions to some reactors—starting with the Turkey Point power plant in South Florida. Environmental groups filed interventions to halt the plan, arguing that a combination of more intense hurricanes and sea level rise would threaten the low-lying plant in ways that regulators had not adequately considered. In February, the NRC reversed the extension for Turkey Point and other plants pending a more extensive environmental review.
So far, most production cuts are due to warming waters—not just in the Rhône and Garonne, but in places like the Tennessee River in the US, and in the coastal seas where many more plants are sited. In recent years, nuclear plants across Northern Europe have been forced to shut down or reduce output because seawater became too warm to safely cool the reactor cores. Over the past decade, the Millstone power plant in Connecticut saw a series of shutdowns on hot summer days until regulators raised the temperature limit of its cooling waters by 5 degrees Fahrenheit.
Given the relative rarity of intense heat waves and outages due to storms, the climate-related hiccups have a small impact on energy production overall—affecting less than 1 percent of annual output for EDF on average, for example. But the impact is growing as temperatures continue to rise. In an analysis published in Nature Energy last summer, a Stanford researcher found that there had been eight times the number of heat-related outages in the 2010s compared with the 1990s. In a 2011 study on the impact of warming on nuclear cooling systems, EDF scientists projected a 3 degree Celsius increase in the Rhône’s temperature by 2050, spelling more potential for shutdowns during heat waves.
And those disruptions can come at critical times, like summer heat waves when demand for energy is high. In France, where nuclear power ordinarily supplies 80 percent of the country’s needs, the current shutdowns are arriving at an especially bad time, as Europe scrambles to shore up energy reserves because of gas and oil shortages due to the war in Ukraine.
Adapting the existing fleet can be difficult, says Thibault Laconde, CEO of Callendar, a Paris-based startup that advises companies on climate risk. It’s not possible to move a facility that has already been built, and plants are expensive to overhaul. It might be possible to redesign pipes to reach for deeper, colder water, or add in newer heat-exchange systems that reduce the need for water, as many French plants did after the country’s record-breaking 2003 heat wave. But the costs are typically large, and the gains in efficiency small, Laconde says.
Building from scratch is easier. “The key issue is when we start building new plants, how can we take into account the impact of climate change for the full lifespan of the plant to 2080 or 2100,” Laconde says, noting that France’s new generation of reactors, recently announced by President Emmanuel Macron, are mostly being built by the coasts. He adds that nuclear power works just fine in hotter climates, like Spain or the United Arab Emirates, because those plants were built to withstand it. “I believe it’s possible to adapt,” Laconde says.
In the US, the sole desert-based nuclear facility, the Palo Verde plant in Arizona, relies on municipal wastewater rather than rivers or seas, though the facility has struggled with rising costs as more industries compete for limited supplies. Doug True of NEI puts more stock in a proposed new generation of smaller nuclear reactors, some of which use molten salts or air-based cooling and are less dependent on having water sources on hand.
In the meantime, in France, regulators are expecting a long summer ahead. While the heat may pass, low water levels can persist, resulting in cutbacks that last for weeks or months. EDF recently told reporters that it expects more cuts in the coming months as water levels continue to fall—leaving the country hoping for the relief of cold, hard rains.
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