Gravelines Nuclear Plant Hits 15.6% Shortfall After Jellyfish Clog
Jellyfish swarms forced repeated reactor shutdowns at France's Gravelines plant, causing a 15.6% nuclear output dip.
Key points
- Jellyfish clogged cooling pumps at Gravelines, forcing three reactors offline and causing a 15.6% nuclear output shortfall.
- Unit 3 was shut down again on August 26 due to a new jellyfish surge, delaying full plant restoration until August 30.
- EDF installed cameras at intake canals and filter screens to detect marine blockages after the second consecutive year of incidents.
Gravelines nuclear power plant in northern France experienced a significant production disruption in August when a massive swarm of jellyfish clogged the facility's cooling systems. The event forced operators to take three reactors offline, resulting in an estimated 15.6% shortfall in France's total nuclear power generation for the period.
As one of Europe's largest nuclear sites with a capacity of 5,460 MW, the Gravelines plant faced this biological intrusion for the second consecutive year. The blockage of cooling pumps triggered automatic safety protocols, leading to the immediate shutdown of Units 3 and 4, while Unit 2 was manually taken offline and Unit 1 had its output reduced by half.
Reactor status fluctuated over three weeks
Operational recovery was gradual and interrupted by repeated influxes of marine life. Unit 2 was reconnected to the national grid on August 13, but Units 3 and 4 remained offline. A subsequent jellyfish surge on August 26 forced a proactive shutdown of Unit 3, extending the duration of the disruption before full restoration.
The plant's seawater filtration systems, including preliminary screens and rotating filter drums, sustained significant blockages. By August 30, Unit 4 was finally reconnected, bringing five of the six reactors back online. Unit 5 remained offline during this entire period for its scheduled ten-year inspection and maintenance.
Enhanced monitoring systems deployed for safety
In response to the 2025 incident, EDF Energy implemented stricter monitoring protocols to detect and mitigate future biological blockages. These measures include the installation of cameras at intake canals and on filter drum screens to identify incoming obstructions from fish and jellyfish before they impact pump efficiency.
Company officials confirmed that the events had no adverse impact on plant safety, personnel welfare, or the surrounding environment. The incident highlights the growing operational challenges nuclear facilities face from changing marine ecosystems, necessitating proactive technological adjustments to maintain grid reliability.
