Jellyfish invasion disrupts France’s nuclear power generation as a large swarm clogged cooling-water pumps at Gravelines, Western Europe’s largest nuclear power station, forcing several reactors offline or to operate at reduced capacity. The incident contributed to a record 20.4% of France’s nuclear generating capacity being unavailable on Wednesday, according to AFP calculations based on EDF data. France relies on nuclear energy for around 70% of its electricity, making disruptions across its reactor fleet particularly significant.

The latest outage also came after repeated heatwaves and drought conditions had already affected nuclear production during June and July.

Jellyfish Swarm Hits Five Gravelines Reactors

Gravelines was forced to shut down several reactors after jellyfish entered equipment connected to the systems that draw seawater for cooling.

• EDF reported that only one of the plant’s six reactors was operating at full capacity.
• Three 900-megawatt reactors were completely shut down, while another was operating at half power.
• The sixth reactor was already offline for scheduled maintenance.

The incident is strikingly similar to what happened at Gravelines exactly one year earlier, when a jellyfish swarm disrupted operations for two days.

EDF said the latest event did not affect the safety of the plant, its workers or the environment. Teams were working to clean the pumping equipment and restore the affected reactors to the national grid.

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Fishing Boats Deployed to Clear Jellyfish

The response has included round-the-clock preventive fishing operations near the plant. Three vessels have been deployed to capture jellyfish using trawlers and release them farther offshore.

The exact species responsible for the latest incident had not been identified at the time of the report.

Heat and Drought Add Pressure

The jellyfish problem is only one part of France’s wider nuclear-power challenge this summer. Other reactors have experienced shutdowns or reduced production because extreme heat and drought have affected the availability and temperature of water needed for cooling.

Before the latest Gravelines incident, France’s nuclear production capacity had already recorded a 15.6% shortfall, according to AFP.

During Wednesday’s peak, EDF recorded its highest level since 2015 of outages attributed to “environmental constraints” or external environmental causes. Thirteen of the company’s 57 reactors were either offline or operating below full capacity.

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Why Are Jellyfish Becoming a Concern?

Experts have pointed to several factors that could create favourable conditions for jellyfish, including warming seas, overfishing and plastic pollution. However, the precise causes of individual jellyfish blooms can vary, and the species involved in the Gravelines incident had not yet been confirmed.

Large jellyfish swarms have disrupted nuclear facilities in other countries as well. A Swedish nuclear plant experienced a three-day shutdown after a jellyfish incident in 2013, while a major jellyfish-related disruption occurred at a Japanese nuclear facility in 1999.

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A New Challenge for Coastal Nuclear Plants

The Gravelines incident illustrates how environmental conditions can create unexpected operational challenges for coastal power stations. Nuclear reactors require reliable cooling systems, and anything that obstructs seawater intake equipment can force operators to reduce or suspend generation.

For France, the combination of marine disturbances, extreme heat and drought presents a more complicated challenge than any single outage. As climate and ocean conditions continue changing, Jellyfish invasion disrupts France’s nuclear power generation and becomes part of a broader discussion about how vulnerable critical energy infrastructure is to environmental extremes.

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