Summer river water temperatures in France and Switzerland were nearing or exceeding 80 degrees Fahrenheit. Between the high heat and a marine jellyfish bloom, at least seven reactors were shut down and several others had to reduce output. Most nuclear reactors pump cooling water from nearby rivers or the sea, returning heated water to the environment. This can harm biodiversity as the hotter water has less oxygen, can be subject to algal blooms, and can cause large kills of fish and other organisms.
Extreme temperatures caused by global warming can mean that reactors are sometimes unable to be cooled as the water bodies become too hot, or that reactors must shut down in order to prevent raising the water temperature to unsafe levels.
Both France and Switzerland have safeguards intended to curtail reactor operations when river temperatures reach a certain level. However, during a major 2022 heatwave, both countries allowed reactors to continue operating with water hotter than the allowed maximum, in order to avoid electricity shortages.
Simultaneously, numerous swarms of jellyfish, expanding due to warmer waters, clogged water intake systems and caused four reactors in France to shut down in August.
Reactors have been forced to reduce output or shut down on several occasions in recent years. Switzerland, which produces about one third of its energy from four nuclear reactors, plans to phase them out by 2033. France’s 56 reactors account for about 65% of the country’s electricity.
A 2024 report by the Cour des Comptes, a French administrative court tasked with auditing government spending, projected the “country may see the amount of electricity lost because of climate-related shutdowns triple or quadruple by 2050.”
⸺ Euronews.com, July 2, 2025; New York Times July 3, 2025
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