- EDF shut down four reactor units at France’s Gravelines nuclear plant after a massive jellyfish swarm clogged its cooling water pumps.
- Scientists link such incidents to warming seas, invasive species, and human activity, and are exploring early-warning methods.
French utility Electricite de France (EDF) shut down four reactor units at its Gravelines nuclear power plant after a massive swarm of jellyfish clogged the facility’s water pumping stations.
EDF said three reactor units automatically went offline at the plant on the English Channel on Sunday evening, August 10, followed by a fourth early Monday morning, August 11. The company stressed that the shutdowns posed no risk to the safety of the plant, employees, or the environment.
“These shutdowns result from the massive and unpredictable presence of jellyfish in the filter drums of the pumping stations,” EDF said in a statement. Teams inspected the site to prepare for a restart and plan to bring the reactors online on Thursday, August 14.
The shutdown halted all electricity generation at France’s largest nuclear station by capacity because EDF had already placed its two other units offline for maintenance. EDF supplied the grid with power from different sources, including solar, and ruled out any risk of a shortage.
Marine biologists link rising jellyfish numbers near Gravelines, between Dunkirk and Calais, to warmer waters and invasive species. Derek Wright, a marine biology consultant with the U.S. National Oceanic and Atmospheric Administration, said climate change has extended the reproductive window for jellyfish in the North Sea.
“Jellyfish also hitch rides on tanker ships, enter ballast tanks in one port and emerge halfway across the globe,” Wright told Reuters. Scientists identified the invasive Asian Moon jellyfish in the North Sea in 2020, a species that has previously clogged cooling systems at nuclear plants in China, Japan, and India.
The Bulletin of the Atomic Scientists reported in 2021 that jellyfish swarms regularly disrupt nuclear plants, sometimes forcing costly shutdowns. Sweden suffered a three-day closure in 2013, while Japan experienced a 1999 incident that cut power output sharply.
EDF said it has not yet identified the species responsible for this week’s shutdown but noted such events remain rare, with the last one affecting its operations in the 1990s.