Heatwave and jellyfish influx into pump stations push French nuclear unit unavailability to 20.4%

The heatwave sweeping across multiple regions of France is impacting the country's electricity production. Several nuclear reactors operated by Électricité de France (EDF) have been shut down or derated due to "environmental restrictions" or "external environmental factors," with the unavailability rate of affected units rising to 20.4% before 10:00 AM on August 12, marking a recent high.

Of France's 57 nuclear reactors, 13 are currently affected. Among them, 8 units are fully shut down: Bugey Unit 3, Cattenom Unit 1, Chooz Units 1 and 2, Golfech Unit 2, and Gravelines Units 2, 3, and 4; another 5 units are operating below rated power, including Saint-Alban Unit 2, Tricastin Units 1 and 4, and Gravelines Units 1 and 6.

During drought or high-temperature weather, reduced river flow and elevated water temperatures can limit the intake and discharge capacity of cooling water at nuclear power plants. To comply with environmental protection and biodiversity requirements, EDF typically needs to reduce unit output, or suspend power generation entirely in severe cases.

The direct cause of this round of curtailments also includes a massive influx of jellyfish into the seawater pump station at the Gravelines Nuclear Power Plant. Located in northern France, this plant is one of the largest nuclear power stations in Western Europe. After jellyfish accumulation affected the water intake system, EDF temporarily shut down or derated 5 of the station's 6 units.

As of around 10:00 AM on August 12, Gravelines Units 1 and 6 had resumed full-power operation; Unit 5 remained under planned maintenance. Gravelines Unit 2, still offline, was scheduled to be reconnected to the grid at 11:00 PM that evening.