Jellyfish Swarm Forces Shutdown of Three Reactors at French Nuclear Plant

A massive swarm of jellyfish has forced the shutdown of three reactors at France's Gravelines nuclear power plant, operator EDF confirmed. The incident, which occurred late Monday, triggered preventive measures that were introduced last year following a complete outage at the facility.

The plant, located in northern France and cooled by water drawn from a canal connected to the North Sea, has six reactors, each with a capacity of 900 megawatts. Reactors 2, 3, and 4 were taken offline due to the swarm, while Reactor 1 has been limited to 50% of its output as a precaution. Reactor 5 was already offline for scheduled maintenance, and Reactor 6 remains fully operational.

Following last year's full shutdown, EDF implemented new monitoring and trawling techniques to mitigate the impact of such events. Fixed cameras have been installed at the intake canals and on filter drum screens to detect blockages early. The company has also partnered with a French fishing organisation and a sea rescue group, which monitor for swarms and can trigger targeted trawling operations to reduce density before the jellyfish reach the plant.

Fishing boats were deployed on Saturday after an initial alarm, which helped limit the impact. Jellyfish already at the site are being removed using vacuum trucks. An engineer noted that no new jellyfish are arriving, so cleanup is nearing completion, which should allow for a quick restart of the affected units.

EDF stated that the situation poses no risk to the safety of the facility, personnel, or the environment. Scientists have warned that such events could become more frequent due to global warming, invasive species, loss of predators, and over-fishing.

Separately, EDF is also dealing with heat-related constraints on its nuclear fleet, as a fifth heatwave is expected to intensify through the week. One reactor in the north has been offline for most of the summer due to low river levels, while another has faced limited restarts and remained largely offline for most of July.