On 14 August 2025, four out of six reactors at France’s Gravelines nuclear power plant were shut down due to a swarm of jellyfish clogging a cooling-water intake canal from the North Sea. Rising ocean temperatures likely contributed to this jellyfish bloom and extended their season. This incident followed earlier constraints on 22 July when Electricité de France temporarily reduced output at the Golfech nuclear plant due to soaring river temperatures exceeding cooling thresholds. Similarly, at the Bugey nuclear plant near Lyon, operations were curtailed from 16 July until 20 July during a heatwave that raised Rhône River temperatures above 26°C. In Germany, PreussenElektra’s Isar 2 reactor also reduced output during a mid-July heat surge, impacting approximately 1,400 MW.
In July 2025, France experienced a nuclear derating loss of 5 TWh to 6 TWh, leading to an economic impact exceeding €400 million, as reported by grid operator Réseau de Transport d’Électricité. This incident marks the third consecutive summer facing weather-related nuclear output constraints across Europe, affecting revenues from baseload generation during peak summer prices.
