Jellyfish Swarm Forces Shutdown of Three Reactors at France's Gravelines Nuclear Plant

France's Gravelines nuclear power plant experienced significant disruption after a large swarm of jellyfish clogged its cooling systems. The incident led to the shutdown of three reactors (2, 3, and 4) and reduced the output of a fourth (reactor 1) to half its normal capacity. A fifth reactor was already offline for scheduled maintenance, leaving only one of the site's six units functioning at full power.

Gravelines, a major nuclear facility in France with a total capacity of 5.4 gigawatts, relies on seawater from a canal connected to the North Sea for cooling. The jellyfish accumulated on filters, restricting the necessary water flow. EDF, the plant operator, assured the public that the situation did not endanger the plant's safety, its personnel, or the environment.

This disruption follows a similar, more extensive shutdown at the same plant in 2025, which was also caused by jellyfish. In response to the previous incident, EDF had implemented enhanced monitoring measures. These included installing fixed cameras along intake canals and around filter screens to detect marine life early. Fishing boats were also deployed to reduce the density of the swarm before it reached the plant's intake, and vacuum trucks were used to clear jellyfish already within the system. EDF reported that the situation was improving as no new jellyfish were detected in the vicinity.

“

The operator said the incident did not pose a threat to the safety of the plant, its workers or the environment.