Three reactors at the Gravelines nuclear power plant in northern France have been shut down after a massive influx of jellyfish blocked the filters in the seawater pumping stations used to cool the facility. A fourth reactor is running at half capacity, a fifth was already offline for routine maintenance, and only one of the plant's six reactors is currently operating at full power. The operator, French energy company EDF, has stated that the shutdowns pose no risk to the safety of the installations, staff, or the environment.

Gravelines, located on the English Channel coast between Dunkirk and Calais, is home to the largest nuclear power plant in Western Europe. The plant draws seawater from the Channel to cool its reactors, making it vulnerable to seasonal jellyfish migrations. Experts point to a combination of overfishing and rising sea temperatures — linked to climate change — as the main drivers behind increasingly frequent and large jellyfish swarms along the northern French coast. Nuclear technology expert Emmanuelle Galichet told Reuters that the plant supplies electricity to a significant number of households and businesses across France and Europe, meaning the disruption carries real consequences for energy supply.

The financial toll could also be considerable. According to Galichet, each reactor that sits idle for a single day represents a net loss of approximately one million euros for EDF. The company indicated that reactors would be restarted one by one, with full capacity expected to be restored by Friday. The jellyfish crisis comes on top of an already difficult summer for French nuclear output, with drought and heatwaves having forced plants across the country offline for a record number of hours.

This is not the first time Gravelines has faced this precise problem. Exactly one year ago, four reactors at the same plant were automatically shut down by a jellyfish swarm, and the last affected reactor took nearly ten days to be fully reconnected to the national grid. The phenomenon is not unique to France — nuclear plants in Japan, Scotland, Sweden, and California have all previously experienced operational disruptions caused by jellyfish. Scientists warn that warmer oceans are also increasing the prevalence of algae blooms, which could pose a similar threat to coastal nuclear infrastructure in the future.