A massive arrival of jellyfish forced the automatic shutdown of four reactors at the Gravelines nuclear plant in northern France, the largest complex in Western Europe by capacity. The operator, EDF, confirmed that the affected units were shut down following reactor protection protocols, while the other two were already shut down for maintenance.
The incident, unusual but not unprecedented, occurred when the filtration systems of the pumping stations that supply seawater to the cooling circuits collapsed. According to the company, no damage was reported, nor was the safety of the facilities, staff, or the environment compromised.
What exactly happened
EDF reported a "massive and unpredictable presence" of jellyfish. in the filter drums of the pumping stations, a non-nuclear area of the site. Units 2, 3, and 4 were automatically shut down on Sunday night, between 23:00 p.m. and midnight, and Unit 6 was shut down on Monday at 06:20 a.m., in accordance with safety devices.
The blockage occurred in the finest filtersThe gelatinous organisms would have overcome the initial grids and ended up blocking the drums, which only allow water to pass through. The protocol calls for halting production to protect the equipment and allow the removal and cleaning of the accumulated material.
Gravelines is cooled with water from a canal connected to the North Sea, which explains the jellyfish intrusion into the pumping chain. The company activated intervention teams to clear the intakes and inspect the system before restarting.
Impact on operation and safety
The electricity company emphasizes that there was no danger for the facilities, personnel, or the environment. The shutdown was preventive and automatic, and the teams are mobilized for diagnostics and cleaning work before the affected units return to service.
No supply problems are anticipated on the French grid due to this incident, according to EDF. The company operates the country's fleet of 57 reactors, which provide a significant portion of the nation's electricity, allowing it to cope with specific incidents like this.
The reactivation schedule is progressiveThe initial forecast was for a first restart starting on Thursday, although market sources indicated that only one unit could return that day, with the rest gradually returning towards the end of the week, depending on how the concentration of jellyfish on the coast evolves.
Causes, species involved and background
The species involved has not been confirmed by the operator., but agencies like Reuters point to Rhizostoma pulmo (jellyfish). The increased persistence of these swarms is associated with warmer summers and currents that push schools toward canals and water intakes, which can also favor the appearance of jellyfish near nuclear plants.
Ocean warming and overfishing Among the factors that favor these proliferations are higher temperatures that accelerate the jellyfish's life cycle, while the reduction in natural predators (such as some tuna) facilitates their expansion. The temperature of the sea also influences the presence of these species in areas near the facilities.
It's not the first time it happens Neither at Gravelines nor at other coastal plants. The French complex already experienced a similar episode in the early 90s, and in the 2010s, facilities in the United States, Scotland, Sweden, and Japan experienced shutdowns due to jellyfish blockages. In 2021, the Torness plant (Scotland) halted production for several days due to a similar incident.
The importance of Gravelines for the electrical system It is notable: it has six reactors of 900 MW each (around 5,4 GW in total) and is expected to house two EPR2s of 1.600 MW from 2040. Its location, close to the Belgian border and with water intake from the North Sea, conditions the operational challenges in periods of high presence of marine fauna.
This episode highlights how unusual natural factors can temporarily disrupt critical infrastructure, even with robust protection systems. With safety guaranteed and cleanup work underway, the plant aims to gradually resume production as soon as environmental conditions permit.