French Nuclear Plant Shut down by ‘Massive' Jellyfish Swarm

Yomiuri Shimbun

2 days ago

A major nuclear power plant in northern France temporarily shut down because of the presence of a 'massive and unforeseeable' swarm of jellyfish inside its cooling system.
Électricité de France, the national electric utility company that operates the Gravelines nuclear power plant, said three reactors automatically shut down Sunday night and a fourth on Monday morning after jellyfish appeared in the filtration drums of the plant's water pumping stations, which it said are 'located in the non-nuclear part of the facilities.' This means all of the plant's reactors were nonoperational as of Tuesday, because its remaining two reactors were previously shut for maintenance.
The automatic shutdown 'had no impact on the safety of the facilities, the safety of personnel, or the environment,' EDF said.
The French utility said its teams were working to safely restart the reactors. Laura Mandin, a spokeswoman for EDF, said in an emailed statement Tuesday that the production units were expected to restart in the coming days, adding that it would be 'a gradual process.'
Cathy Lucas, an associate professor in marine biology at the University of Southampton in Britain, said EDF's report of a 'massive' presence of jellyfish could be a reference to a jellyfish bloom – when a specific area suddenly experiences a big increase in its jellyfish population after the gelatinous invertebrates begin to reproduce more quickly or find an environment that favors their survival.
Jellyfish are highly adaptable. Many species of jellyfish grow rapidly when the water is warm and in a specific range of salinity. This summer's heat wave in Europe – with temperatures exceeding 100 degrees Fahrenheit (38 degrees Celsius) in parts of the continent – has probably created ideal conditions for certain types of jellyfish to reproduce more rapidly and in higher numbers, Lucas said.
Other factors promoting jellyfish blooms include overfishing, which helps eliminate many of the jellyfish's competitors and predators, leaving more food for them, said Lucas.
When the weather is warm and the sea is calm, jellyfish tend to float closer to the surface of the water, Lucas added – and because they are weak swimmers, once they form a bloom, it is difficult for them to swim away. This could explain how jellyfish in the North Sea could have gotten sucked into the systems at Gravelines, she added.
Jellyfish forced a shutdown at the Torness nuclear plant in Scotland in 2011 and at the Oskarshamn plant in Sweden in 2013, among other incidents. In both cases, the shutdown and cleanup lasted a few days.
The Gravelines nuclear power plant is on the coast of the North Sea, about halfway between Calais and Dunkirk in northern France, and uses seawater to cool its reactors. The water is filtered through large drums designed to capture fine particles before being processed through pumping stations. Typically, the filters help stop sea life and other marine elements from getting into the pumping stations.
Ronan Tanguy, a nuclear engineer at the World Nuclear Association, told the BBC that the jellyfish's gelatinous bodies may have allowed them to 'evade the first set of filters then get caught in the secondary drum system.' He said the shutdown would have been automatically triggered for safety when the blockage prevented the systems from pumping enough water. He told the BBC that the incident was a 'non-nuclear event' and more a 'nuisance' for employees to clean up.
Mandin said EDF does not know the species of jellyfish involved in the incident.
The Gravelines plant has six pressurized water reactors that started operating between 1980 and 1985. Together, they produced about 32.7 terawatt-hours of electricity in 2024, equivalent to 9 percent of France's nuclear power generation, according to EDF. The plant generates enough power to meet up to 70 percent of the Hauts-de-France region's electricity needs, EDF says.