France has temporarily taken several nuclear reactors offline as an intense heatwave pushes river temperatures beyond environmental limits, highlighting a growing challenge for nuclear power plants operating in a warming climate.

State-owned utility EDF shut down two reactors on Thursday at the Nogent-sur-Seine nuclear power plant on the Seine River and the Bugey plant on the Rhône after water temperatures rose high enough to trigger environmental protection rules. 

Earlier in the week, another reactor at the Golfech plant on the Garonne River was also taken offline, while output was reduced at several additional sites across the country. The measures were taken to protect river ecosystems, not because of reactor safety concerns.

Why heatwaves affect nuclear power

According to Euronews, France’s reactors rely heavily on river water to remove excess heat generated during electricity production. After passing through the plant’s cooling systems, the water is discharged back into the river.

During normal conditions, the temperature increase is carefully regulated. But during prolonged heatwaves, rivers are already unusually warm. Returning additional heated water can threaten fish, aquatic plants, and other wildlife, requiring operators to reduce power output or temporarily shut reactors down to comply with environmental regulations.

The restrictions illustrate an often-overlooked aspect of nuclear power. Although reactors do not emit carbon dioxide while generating electricity, many depend on abundant supplies of cool water to operate efficiently.

Nuclear remains secure despite reactor outages

The temporary shutdowns come at a difficult time for France, which generates roughly two-thirds of its electricity from nuclear power, supplied by EDF’s fleet of 57 reactors.

Despite the reduction in output, French grid operator RTE said the country continues to have sufficient generating capacity to meet electricity demand, even if additional reactors are temporarily affected. Reuters also reported that the current heatwave reduced French nuclear output by around 4 gigawatts, roughly seven percent of electricity demand at one point, as river temperatures climbed above operational thresholds.

Electricity markets have nevertheless felt the impact. Reuters noted that reduced nuclear generation, combined with higher cooling demand and weaker wind generation, pushed wholesale electricity prices in France and Germany to their highest levels since early 2025.

A recurring challenge for the nuclear industry

This is not the first time France has faced heat-related restrictions on nuclear generation. Similar output reductions occurred during major European heatwaves in recent years as rivers became too warm to safely absorb additional cooling water. In some exceptional circumstances, EDF has previously received temporary regulatory exemptions when the electricity supply was at risk, although no such exemptions have been requested during the current heatwave.

According to Le Monde, several other EDF plants remain under close monitoring, with additional reductions possible if river temperatures continue to rise.

Climate change is reshaping energy planning

The current heatwave has stretched far beyond France. Much of Western Europe has experienced record-breaking temperatures, with France recording its hottest June day since national records began in 1947. The extreme weather has disrupted transport, forced school closures, and placed millions of people under heat alerts.

Nuclear power is widely viewed as one of the world’s most important low-carbon electricity sources, yet many existing plants were designed around historical river temperatures that are becoming less reliable as climate change intensifies.

As Europe experiences increasingly frequent and prolonged heatwaves, utilities may need to invest in alternative cooling technologies, upgraded infrastructure, or revised operating strategies to maintain reliable electricity production while protecting freshwater ecosystems.

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