Swarm of jellyfish shuts nuclear power plant in France

‘Massive and unpredictable’ swarm entered filter drums that pull in water, Gravelines operator EDF says

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Jillian Ambrose Energy correspondent

Mon 11 Aug 2025 06.15 EDT

A swarm of jellyfish has forced the shutdown of one of the largest nuclear power plants in France after entering the water intake systems used to cool the coastal reactors.

Three reactors at the Gravelines nuclear power plant in northern France shut down automatically late on Sunday, according to the French nuclear company EDF, after the filter drums of the pumping stations became packed with a “massive and unpredictable” swarm of the marine creatures.

The entire nuclear plant, capable of powering about 5m homes, was brought offline when a fourth reactor shut down shortly after the free-swimming invertebrates jammed the power plant, which had already lost its two other reactors for planned summer maintenance work.

EDF, which is owned by the French state, said the event did not affect the safety of the facilities, staff or the environment. There does not appear to be any change to electricity exports from France to the UK.

The Gravelines plant draws water used in its cooling systems from a canal connected to the North Sea, which is home to several native species of jellyfish often seen around the shoreline in the summer when the waters are warmer.

Jellyfish have a long history of derailing the normal operations of coastal power plants, which tap the ocean for the vast amounts of cool water needed to keep temperatures in check.

The repeated problems caused by unexpected jellyfish numbers prompted scientists at the University of Bristol to develop an “early warning tool” to predict the sudden, en masse appearance of jellyfish swarms that might disrupt coastal power plants.

The Torness nuclear plant in Scotland, which is also owned by EDF, was forced to shut for a week in 2021 after jellyfish clogged the seaweed filters on its water intake pipes, a decade after jellyfish shut the plant for a week in 2011.

Jellyfish swarms have also closed nuclear and coal power plants in Sweden, the US, Japan, and even caused a major blackout in the Phillipines in 1999 that some mistakenly feared was linked to the Y2K bug or a government coup.