Nuclear power plants in France and Switzerland were forced to shut down or reduce output between July 1^st and 3^rd, 2025, because a major heatwave raised river water temperatures above regulatory cooling thresholds.

A severe heatwave affecting much of Europe over the past ten days forced shutdowns and output reductions at nuclear power plants in France and Switzerland, as high air temperatures raised the temperature of river water used for cooling beyond regulatory limits.

Axpo is the operator of the Beznau nuclear power plant in Switzerland. It shut down one reactor and reduced output at another due to river water temperatures exceeding seventy-seven degrees Fahrenheit. The Swiss Federal Nuclear Safety Inspectorate (ENSI) regulations demand immediate action when cooling water from the Aare River exceeds defined safety limits, both to protect plant integrity and prevent the release of hot water back into the river ecosystem.

In France, Électricité de France (EDF) shut down the Golfech nuclear power plant on July 1^st, after the Garonne River hit the regulatory maximum intake temperature of eighty-two degrees Fahrenheit. EDF also suggested that output restrictions at other nuclear sites, such as Blayais and Bugey, were possible amid the heatwave, though no specific operational changes at those locations were confirmed by July 3^rd.

The French Nuclear Safety Authority and Radiation Protection (ASNR) mandates limits on the temperature of both cooling water intake and discharge water to mitigate risks to riverine biodiversity and comply with environmental protection standards.

Both countries have established contingency measures and reserve margins designed to minimize disruptions to the population due to heightened temperatures of river water. No widespread blackouts have been reported as of July 3^rd.

Nuclear power plants depend on river, lake or seawater for cooling reactor components. Under normal circumstances, water is drawn from a local source, used to transfer heat from the reactor systems, and returned to the environment at a higher, but regulated, temperature.

However, during periods of elevated air temperature, the efficiency of this system is reduced as the intake water is already warm, limiting its cooling capacity. Releasing hotter water into rivers during these events poses additional risks. These include potential harm to aquatic life and reduced oxygen levels, both of which can threaten biodiversity.

European environmental regulations set strict limits on the maximum allowable temperature for water discharged from nuclear plants. This forces operators to curtail or cease operations when the thresholds are reached.

The heatwave began in the last days of May of this year, intensified by mid-June, and is expected to persist into early July. There are forecasts indicating that temperatures could remain above one hundred- and four-degrees Fahrenheit across southern and central Europe through July 10^th.

During this period, Portugal recorded a maximum temperature of one hundred- and sixteen-degrees Fahrenheit on June 29^th, Spain experienced values above one hundred- and four-degrees Fahrenheit in cities including Seville and Madrid, and France registered its hottest June on record, with new temperature records set in the Alps.

At the same time, the Mediterranean Sea is experiencing a record marine heatwave, with sea surface temperatures exceeding thirty degrees in some coastal areas and running more than nine degrees Fahrenheit above seasonal averages.

At least eight deaths have been caused directly by the heatwave by early July, including fatalities resulting from heatstroke during recent wildfires in Spain and France. Italy has also reported heat-related deaths and a significant increase in hospital admissions related to the heat, with some regions experiencing up to twenty percent more cases than average.

France has responded to the heat emergency by closing schools and public attractions, including the top of the Eiffel Tower, and issuing nationwide health alerts.

Greece has seen mass evacuations, with approximately 1 fifteen hundred people displaced on Crete due to wildfire risk. Germany and the United Kingdom have experienced record-breaking temperatures, heat-related injuries, and additional wildfires.

French Authority for Nuclear Safety and Radiation Protection