French Nuclear Output Fell Almost 9% in July 2026 Heatwave, Carbon Brief Says
Power production across the French nuclear fleet dipped by almost 9% during the July 2026 heatwave, with three of the country's 57 reactors taken offline and output throttled at seven more, Carbon Brief reported.
Carbon Brief put the earlier demand spike at almost 20%, measured on daily electricity consumption in France through a two-week heatwave in June 2026.
Nuclear supplies around 70% of French electricity, Carbon Brief said, leaving the country's supply unusually sensitive to reactor curtailments.
Cooling water sits at the centre of the problem. France hosts around 60 of the 440 river-cooled reactors worldwide and another seven operate elsewhere in Europe, with river-cooled units representing 14% of the global fleet, according to Carbon Brief.
Carbon Brief cited an article in Forbes stating that each additional degree Celsius costs a nuclear plant around 0.6-1% in cycle efficiency.
Measured over a full year, the losses are far smaller. Heatwaves trimmed annual nuclear generation by 0.6% on average between 2003 and 2022, Carbon Brief reported, citing a recent study co-authored by McMaster University researcher Michael Tadrous.
Only once has a national nuclear fleet given up more than 1% of its yearly nuclear output to heat- and drought-related curtailments, Tadrous said: France in 2003, at 1.3%.
Reactors in Romania, Hungary and Serbia have been hit by low water levels on the Danube this summer, and a Swiss reactor shut because river temperatures ran too high, according to Carbon Brief.
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