Nuclear power plants shut down in France and Switzerland as heatwave impacts river cooling

A severe heatwave affecting much of Europe over the past 10 days led to shutdowns and output reductions at nuclear power plants in France and Switzerland, as high air temperatures pushed river water used for cooling beyond regulatory limits.

Axpo, the operator of the Beznau nuclear power plant in Switzerland, shut down one reactor and reduced output at another due to river water temperatures exceeding 25°C (77°F). Swiss Federal Nuclear Safety Inspectorate (ENSI) regulations require immediate action when cooling water from the Aare River exceeds defined safety limits, both to protect plant integrity and prevent the release of excessively heated water back into the river ecosystem.

In France, Électricité de France (EDF) shut down the Golfech nuclear power plant on July 1, after the Garonne River reached the regulatory maximum intake temperature of 28°C (82°F). EDF also indicated 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.

The French Nuclear Safety Authority (ASN) mandates limits on both water intake and discharge temperatures 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, and no widespread blackouts have been reported as of July 3.

Nuclear power plants depend on river or seawater for cooling reactor components. Under normal circumstances, water is drawn from a local source, used to absorb and 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 compromised as the intake water is already warm, limiting its cooling capacity. Releasing even hotter water into rivers during these events poses additional risks, including 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, forcing operators to curtail or cease operations when the thresholds are reached.

The heatwave began in the last days of May, intensified by mid-June, and is expected to persist into early July, with forecasts indicating that temperatures could remain above 40°C (104°F) across southern and central Europe through July 10.

During this period, Portugal recorded a maximum temperature of 46.6°C (116°F) on June 29, Spain experienced values above 40°C (104°F) in cities including Seville and Madrid, and France registered its hottest June on record, with new temperature records set in parts of the Alps.

At the same time, the Mediterranean Sea is experiencing a record marine heatwave, with sea surface temperatures exceeding 30°C (86°F) in some coastal areas and running more than 5°C (9°F) above seasonal averages.

At least eight deaths have been linked directly to the heatwave by early July, including fatalities resulting from heatstroke during wildfires in Spain and France.

Italy has also reported heat-related deaths and a significant increase in hospital admissions, with some regions experiencing up to 20% more cases than average.

France 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 1 500 people displaced on Crete due to wildfire risk, while Germany and the United Kingdom experienced record-breaking temperatures, heat-related injuries, and additional wildfires.