North. Jellyfish stranding: All affected reactors at the Gravelines nuclear power plant have been restarted.

Following the unusual stranding of jellyfish at the Gravelines nuclear power plant , production unit No. 3, the last one still shut down since this exceptional incident, was reconnected to the national electricity grid on Saturday, and "units 2, 4 and 6 are in operation," EDF wrote on its website on Monday.

Unit 6 was the first to restart after the incident , on August 13, followed by unit 2 the same day. Then reactor 4 was put back into service on August 20. However, it was briefly disconnected "as a precaution" on Saturday for around ten hours due to a "resurgence of jellyfish," EDF explained.

These four production units were automatically shut down between August 10 and 11 following a "sudden and massive" influx of jellyfish into the filter drums of the seawater pumping stations at the site, located on the North Sea. This incident had no impact on the safety of the facilities, the security of personnel, or the environment, according to EDF.

This "did not affect the cooling of the equipment ensuring the safety of the reactors," confirmed the Nuclear Safety and Radiation Protection Authority (ANSR). Gravelines, the largest nuclear power plant in Western Europe, was nevertheless completely shut down for nearly 48 hours, as its two other production units (No. 1 and No. 5) are currently undergoing scheduled maintenance.

The plant had already seen its production disrupted by a massive eruption of jellyfish in the 1990s, according to EDF, and similar cases have also been observed elsewhere in the world, in the United States, Scotland, Sweden and even Japan in the 2010s.

The presence of these gelatinous, stinging marine animals along the coast of northern France is regular and seasonal. However, reports of large schools in the area each summer are becoming more frequent, according to Dominique Mallevoy, head of aquariology at the Nausicaá National Sea Center in Boulogne-sur-Mer (Pas-de-Calais).

Several factors explain the proliferation of jellyfish around the world. Among them are rising ocean temperatures, linked to global warming, and overfishing, which means jellyfish have fewer predators and more plankton available for their own food, according to Mallevoy and other experts.