Jellyfish disrupts Gravelines plant

A swarm of jellyfish clogged the cooling filters at Gravelines, triggering the automatic shutdown of four reactor units.

Jellyfish force French nuclear plant shutdown

A swarm of jellyfish clogged the cooling system at Gravelines, prompting four reactor units to automatically shut down. EDF said there was no impact on safety, personnel, or the environment. The site’s two other units were already down for maintenance, leaving Gravelines temporarily offline.

The jellyfish entered the non-nuclear part of the facility and slipped past the first filters, then became trapped in the secondary drum system, reducing water intake and triggering the shutdown as a precaution. Gravelines is cooled by a canal linked to the North Sea, and it is among France’s largest power plants. Each unit can produce 900 MW, and the six-unit site is a cornerstone of the country’s nuclear output. Nuclear energy accounts for roughly 70% of France’s electricity, according to the World Nuclear Association.

Nuclear engineer Ronan Tanguy explained that the marine animals managed to slip through systems designed to keep them out because of their gelatinous bodies, which enabled them to evade the first stage of filtration before being caught in the second. The incident prompted plant teams to mobilise, carry out diagnostics, and plan interventions to restart production units safely.

This incident shows how a natural event can disrupt critical infrastructure. Cooling systems rely on multiple barriers, but a bloom of marine life can slip through when filters are tested by unusual conditions. The episode highlights the importance of redundancy, monitoring, and rapid restart protocols to minimize downtime at large plants.

With France depending heavily on nuclear power, outages at Gravelines test the resilience of the grid and fuel policy. The case may push operators to rethink water-intake design, screening efficiency, and contingency planning for seasonal marine life while balancing environmental considerations and costs.

Highlights

Restart will test Gravelines’ resilience and the industry’s readiness to shield grids from wildlife disruptions.