A record-breaking heat wave in Europe is warming up the river water that some nuclear power plants use for cooling, prompting operators to shut down at least three reactors at two separate sites.
Late on Sunday, operators shut down one of the two reactors at the Golfech Nuclear Power Plant in southern France after forecasts that the Garonne River, from which it draws water, could top 28 degrees Celsius, or roughly 82 degrees Fahrenheit.
The Beznau Nuclear Power Plant in Switzerland, near the Aare River near the country’s northern border, followed suit, shutting down one of its reactors on Tuesday and the other on Wednesday.
Both plants are designed to keep their reactors at safe temperatures by cooling them with river water, which is then pumped back out at higher temperatures. Regulations in both countries require operators to reduce energy production when the rivers get too hot, in order to protect downstream environments.
The operator of the Beznau plant, Axpo, said that “excessive warming of the already-warm river water during hot summer periods is to be prevented in order not to place additional strain on flora and fauna.” In a statement, Axpo confirmed that a limit of 25 degrees Celsius had been exceeded for several days in a row.
Other river-cooled nuclear reactors, including one at the Bugey plant in southeastern France, have reduced their power generation. Temperatures across Europe have regularly exceeded 100 degrees Fahrenheit this week, though forecasters say relief is on the way over the weekend.
When most reactors in the United States and Europe were built, mainly from the 1960s into the 1980s, they were not designed with climate change in mind. As global temperatures have risen, precautionary power plant shutdowns because of heat have increased in frequency.
While energy losses are typically low, a 2024 report by Cour des Comptes, an administrative court in France that audits and helps to regulate government spending, found that the country may see the amount of electricity lost because of climate-related shutdowns triple or quadruple by 2050.
Nuclear power is France’s top source of energy, with the country’s 18 nuclear plants providing nearly two-thirds of the country’s electricity needs. In Switzerland, nuclear power accounts for roughly a third of all energy consumed.
Neither this week’s shutdown in France nor the one in Switzerland were expected to have significant effects on power generation.
“The Swiss power grid remains stable,” an Axpo statement said. “Other generation capacities, particularly hydropower plants, are able to compensate for the temporary shutdown of the Beznau Nuclear Power Plant.” Local reports indicated that the French grid operator also expected to have sufficient supply to meet energy demand.
In 2022, however, a heat wave, coupled with a drop in generating capacity, prompted France’s nuclear authority to temporarily relax its rules regulating the maximum downstream temperature of water discharge. Similarly, in Switzerland, the Beznau plant continued operating during that year’s hot temperatures.
“This is the first time that the plant has had to be shut down due to water temperature,” a representative of the Swiss Federal Office of Energy said. “In 2022, despite excessively warm water in the Aare River, the plant continued to produce electricity because the electricity supply situation did not allow for a shutdown.”
The Swiss energy office added that a temporary reduction in production had occurred “several times in recent years.”
All nuclear power plants take in and release water, but the amount varies based on their design.
Many plants and animals are sensitive to thermal pollution, which occurs when human activity changes the temperature of natural bodies of water, like rivers. Warmer water holds less oxygen and becomes more susceptible to algal blooms. When power plants suddenly begin operating or turn off, fish can be killed from the sudden changes in temperature.
Affects on wildlife aren’t the only risk that heat waves pose to nuclear power plants. If the water they take in is too hot to begin with, it may not be effective in cooling reactors, making operation unsafe. In 2012, a nuclear plant in Waterford, Conn., was shut down when the surrounding bay became too hot to keep the site cool.
According to Marcus Amme, a member of the European Nuclear Society’s High Scientific Council, all of Switzerland’s nuclear power plants have safety certifications, required by Switzerland’s nuclear regulatory authority, that confirm their facilities can withstand heat waves with a maximum air temperature of at least 40 degrees Celsius, or 104 degrees Fahrenheit.
Sachi Kitaijma Mulkey covers climate and the environment for The Times.
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