Jellyfish clog cooling system forcing shutdown of two reactors at Frances Gravelines nuclear plant

Two reactor units at France’s Gravelines nuclear power plant were shut down on Wednesday and Thursday after more than 200 metric tons of jellyfish clogged the facility’s seawater filtration systems, operator Électricité de France said.

A company spokeswoman told the Deutsche Presse-Agentur that the jellyfish appeared near the plant’s pump station filters overnight. Two of the six reactor blocks were fully powered down as a precaution “to ensure that this situation has no impact whatsoever on the safety of our facilities.” Two additional units were operating at reduced capacity, while the remaining two were already offline—one due to a technical issue and another for maintenance, according to EDF .

As of Thursday, none of the plant’s six reactors were running at full capacity. Unit 6 was taken offline early Thursday, followed by Unit 3 later in the day, EDF confirmed on its website. Units 1 and 2 were operating at reduced power, while Unit 4 remained shut after an earlier jellyfish-related stoppage on Aug. 10, and Unit 5 was down for scheduled maintenance .

The plant, located on France’s northern coast between Calais and Dunkerque, has faced repeated jellyfish disruptions this month and in August 2025. EDF said it has installed monitoring and detection systems to identify jellyfish swarms early, with support from the organization France Pêche Durable. Seven boats are operating around the clock near the plant to capture jellyfish and release them farther offshore .

The spokeswoman said the cause of the jellyfish surge remains unclear, though EDF is working with partners to better understand the phenomenon. She emphasized that the incident poses no risk to the power grid .

Gravelines, one of France’s largest nuclear stations, uses seawater from a canal connected to the North Sea for cooling. Jellyfish activity typically increases in warmer months due to higher plankton levels, experts noted . Similar jellyfish-related shutdowns have occurred at other plants, including Scotland’s Torness in 2011 and Sweden’s Oskarshamn in 2013 .