A surge of jellyfish forced France’s Gravelines nuclear power plant to shut down four of its six reactors this week after the invertebrates clogged the cooling-water intake system, operator Électricité de France (EDF) said. “The automatic shutdown resulted from a massive and unpredictable presence of jellyfish that reduced seawater flow to the reactors,” said EDF, according to BBC News.
Gravelines, situated on the North Sea coast between Dunkirk and Calais, runs six pressurized-water reactors of 900 megawatts each. The 5.4-gigawatt complex normally supplies electricity to roughly five million households—about 8 percent of France’s nuclear capacity—but all units are now offline because two of the six reactors were already in scheduled maintenance. EDF said other French generating stations could cover demand during the low-consumption summer period and stressed that the shutdown posed no risk to public safety or the environment.
The incident began when seawater pumps about 20 kilometres east of Calais drew the jellyfish into intake pipes. The creatures slipped through initial screens and became lodged in deeper filter drums, triggering automatic safety systems that tripped units 2, 3 and 4 just before midnight; unit 6 followed a few hours later. “They were able to pass through the first set of filters and then got trapped in the secondary system,” said Ronan Tanguy of the World Nuclear Association. He called the event a nuisance rather than a crisis.
Marine specialists tied the bloom to higher sea temperatures, overfishing of predators such as tuna, and the spread of the Asian moon jellyfish, first recorded in the North Sea in 2020. “Jellyfish can hitch a ride on tankers, ending up in ballast tanks in one port and being pumped back into the water halfway around the world,” explained marine biologist Derek Wright to CNN. “Not only are they most active in the warmer months, but hot weather increases the level of plankton at the water’s surface, which draws jellyfish from the depths,” said jellyfish expert Ruth Chamberlain. She added that the animals are very weak swimmers, making escape from intake currents nearly impossible.
Jellyfish invasions have interrupted power generation before. Sweden’s Oskarshamn reactor shut in 2013, Japan’s Shimane facility cut output in 1999, and EDF’s Torness plant in Scotland stayed offline for a week in 2021 after similar clogs. Coal-fired stations in China recently removed more than 150 tons of jellyfish from their cooling systems before resuming operations. The International Nuclear Information System recorded several emergency shutdowns linked to jellyfish in 1986–87.
The timing drew attention because technology companies are investing heavily in nuclear-powered data centers to satisfy growing energy demand. Google, Microsoft, Amazon and Meta have signed multibillion-dollar nuclear agreements, some involving campuses adjacent to reactors. The Gravelines incident underlined the vulnerability of critical energy infrastructure to simple natural forces.
EDF crews continued inspections and cleanup on Monday and Tuesday. The utility said up to 3.6 gigawatts of capacity idled by the jellyfish could return to service later in the week, with reactors restarting one by one. Two 1,600-megawatt EPR2 reactors are scheduled for Gravelines by 2040, part of France’s plan to modernize its nuclear fleet even as climate change complicates coastal operations.
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