Extreme heat and falling river levels are forcing nuclear plants across Europe to reduce output or shut down, raising fresh questions over how the continent’s reactors will cope with a warming climate.
Hungary temporarily closed units at its Paks nuclear plant after high temperatures pushed cooling conditions beyond safe operating limits. The shutdown increased the country’s reliance on electricity imports as heat drove up demand across the region.
The problem is not unique to Hungary, most nuclear plants rely on rivers to remove waste heat from their steam systems. When water levels fall, less cooling water is available and when rivers become too warm, operators can be prevented from discharging heated water back into them because of environmental limits.
Plants may then have to cut generation even when electricity demand is rising because homes and businesses are using more air conditioning.
France has repeatedly reduced output from reactors on the Rhône and Garonne during hot summers to avoid overheating rivers. Plants in Sweden and Finland have also been affected by unusually warm seawater, while low river flows have disrupted thermal generation elsewhere in central Europe.
The World Nuclear Association says inland plants using direct river cooling are particularly exposed. France has 12 reactors at four sites that rely heavily on river or lake water without cooling towers, making production more sensitive to high water temperatures.
A European Commission estimate cited by the International Atomic Energy Agency suggests every 1°C rise in cooling-water temperature can reduce nuclear output by around 0.2%.
The IAEA says climate-related losses remain small compared with total nuclear generation but warns heatwaves, drought and changing water availability will become increasingly important without adaptation.
That could include larger cooling systems, alternative water sources, cooling towers and improved forecasting of river flows and temperatures.
Eurelectric has warned extreme heat can hit several parts of the electricity system at once, reducing thermal generation while increasing demand and placing additional pressure on networks.
The risk is particularly significant because nuclear is expected to provide firm low-carbon power when wind and solar output fluctuate.
Europe’s reactors remain major sources of reliable electricity but this summer’s disruption shows they are not immune to climate change.
As heatwaves intensify and rivers run lower, nuclear operators will need to invest in cooling resilience or risk losing output precisely when the power system needs it most.
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