Jellyfish swarm forces three reactors offline at Gravelines nuclear plant in France

A nuclear power station in northern France took three reactors offline after a swarm of jellyfish blocked the seawater pumps that cool the units, the energy group EDF said on Tuesday.

Operational impact and immediate figures

The company said the three reactors were shut on Monday and output at a fourth reactor was reduced by half, leaving only one unit running at full capacity. A sixth reactor was already out of service for planned maintenance.

EDF added that the interruption did not endanger plant safety. "This situation has no impact on the safety of the facilities, the safety of staff or the environment," the company said.

The affected site, the Gravelines plant near the northern city of Dunkirk, is the largest nuclear complex in Western Europe with six reactors of 900 megawatts each.

The shutdown is the latest disruption to France's nuclear output this year, after a series of heat waves and droughts forced EDF to close several reactors in June and July because of extreme temperatures. On the Sunday before the latest stoppage, France recorded a 15.6 percent shortfall in nuclear generation based on EDF data going back to 2015.

Jellyfish have caused temporary closures at the same Gravelines site before — the plant was briefly shut about a year ago after marine life clogged its seawater pumping stations. Similar incidents have forced shutdowns elsewhere, including a three‑day halt in Sweden in 2013 and a major production drop in Japan in 1999.

Scientists point to overfishing, plastic pollution and warming seas from climate change as factors that have created conditions allowing jellyfish populations to expand and bloom more frequently.

Photo: press material from the event