Jellyfish swarm forces EDF to shut down three reactors at Gravelines nuclear plant

Tuesday 11 August 2026 - 11:14

By: Sahili Aya

Jellyfish swarm forces EDF to shut down three reactors at Gravelines nuclear plant

A massive influx of jellyfish has forced French energy company EDF to shut down three reactors at the Gravelines nuclear power plant in northern France.

The unusual incident occurred on Monday, when large numbers of jellyfish entered the plant's seawater pumping stations. EDF announced the reactor shutdowns on Tuesday.

Reactors 2, 3 and 4 were taken offline as a precaution, while the output of reactor 1 was reduced to 50%.

Marine life disrupts cooling operations

The Gravelines facility relies on seawater systems as part of its cooling infrastructure. The sudden concentration of jellyfish around the pumping installations disrupted normal operations and prompted EDF to reduce or stop production at several units.

The incident illustrates how marine conditions and seasonal biological phenomena can affect the operation of coastal industrial facilities.

No information indicating damage to the reactors themselves was reported in the initial announcement. The shutdowns were linked to the presence of jellyfish at the seawater intake systems.

One reactor remains at full capacity

With three reactors offline and another operating at reduced output, only reactor 6 was operating at 100% capacity, according to EDF.

Reactor 5 was already unavailable because of a scheduled maintenance shutdown.

The combination of the planned maintenance and the jellyfish-related disruption significantly reduced the plant's available generating capacity.

Gravelines is one of France's major nuclear sites

Located in the Nord department near the English Channel, the Gravelines nuclear power station is one of France's largest nuclear facilities.

The plant's coastal location provides access to seawater for its cooling systems but also exposes its infrastructure to marine conditions, including the seasonal arrival of large concentrations of organisms such as jellyfish.

The latest disruption demonstrates how environmental factors can create operational challenges even at major electricity-generating facilities.

EDF is expected to monitor the situation and assess conditions at the seawater pumping stations before restoring the affected reactors to normal operation.