Jellies jam French nuclear plant, force it offline

Jellyfish forced a nuclear power plant in France to shut down on Monday. It was not the first jellyfish-induced shutdown, and scorching summer temperatures have already strained France’s large nuclear power sector this year.

Four reactor units at the Gravelines nuclear power plant in northern France shut down automatically between Sunday evening and Monday morning after jellyfish clogged the facility’s water pumping stations, according to French energy group Electricite de France, or EDF. The entire plant, capable of powering about 5 million homes, went offline as two other reactors were already down for scheduled summer maintenance, according to The Guardian.

Despite the disruptions, EDF said there was no risk of power shortages due to the Gravelines shutdown, as other energy sources remained operational.

France gets a higher share of electricity from nuclear power than any other country, but interest is growing in the U.S. because nuclear power facilities can operate around the clock without producing greenhouse gases. Big Tech companies and the Trump administration are united in prioritizing nuclear power, as data centers push up electricity demand.

But the French incident demonstrates that nuclear plants are not immune to other environmental factors that threaten a reliable electricity supply.

How can jellyfish shut down a nuclear plant?

Nuclear power plants require massive amounts of cool water to keep reactor temperatures in check. Coastal plants like Gravelines draw this water from nearby seas or rivers through intake systems equipped with filter drums designed to screen out debris.

Jellyfish can clog those filters when they enter these intake systems in large numbers. EDF described the presence of jellyfish at Gravelines as “massive and unpredictable,” forcing automatic safety shutdowns to prevent reactor overheating, Al Jazeera reported.

Jellyfish-related shutdowns are not unique to France. The phenomenon has forced closures at nuclear and coal plants in Sweden, the United States, Japan, Scotland and China. In 1999, jellyfish caused a major blackout in the Philippines.

EDF said teams were inspecting the Gravelines facility to restart operations “in complete safety,” with the four reactors expected to come back online Thursday. The company noted such jellyfish incidents were “quite rare,” with the last one affecting EDF operations occurring in the 1990s.

How have France’s nuclear plants reacted to hot summers?

Warming temperatures may have contributed to the latest jellyfish incident.

“Jellyfish breed faster when water is warmer, and because areas like the North Sea are becoming warmer, the reproductive window is getting wider and wider,” Derek Wright, a marine biologist with the National Oceanic and Atmospheric Administration, told Reuters.

Heat waves have emerged as another climate-related challenge for France’s nuclear fleet, which provides nearly two-thirds of the country’s electricity. When river water used for cooling becomes too warm, nuclear plants have to reduce power or shut down entirely to protect downstream wildlife.

In July, operators shut down one reactor at the Golfech Nuclear Power Plant in southern France when the Garonne River approached 28 degrees Celsius (82 degrees Fahrenheit). Other river-cooled nuclear reactors, including one at the Bugey plant in southeastern France, reduced power generation during the same heat wave, according to an article in the New York Times.