On August 11, 2025, a massive influx of jellyfish led to the automatic shutdown of four nuclear reactors at the Gravelines nuclear power plant in northern France. The facility, operated by EDF (Électricité de France), is one of the country’s largest nuclear plants, with a total capacity of approximately 5,400 megawatts across its six reactors. The shutdown was triggered when a large number of jellyfish clogged the plant’s seawater-cooling intake pipes, which are critical for regulating the reactors’ temperature and preventing overheating. This incident disrupted the plant’s operations, as the cooling system relies on seawater to dissipate heat generated during nuclear fission.
The jellyfish swarm caused a blockage in the filtration and cooling systems, leading to an automatic safety protocol that halted four of the plant’s reactors. This was a precautionary measure to protect both the plant’s equipment and the surrounding marine environment, as jellyfish and other marine life can be harmed when drawn into the intake pipes. According to posts on X, the French electricity grid managed to handle the sudden loss of these reactors without significant disruption, indicating that the system’s design and contingency measures were effective in maintaining stability. The cooling systems at Gravelines are equipped with protective mechanisms, such as filtration drums, to mitigate the impact of such biological incursions, but the sheer volume of jellyfish overwhelmed these safeguards.
This event is not an isolated occurrence. Jellyfish blooms, which are sudden and dense gatherings of jellyfish, have increasingly disrupted nuclear power plants worldwide due to their ability to clog cooling systems. Similar incidents have been reported at nuclear facilities in Scotland (Torness, 2011), Japan (2011), Israel (2017), the United States (Diablo Canyon, 2008; St. Lucie, 2011), and Sweden (Oskarshamn, 2013). These blooms are often linked to environmental factors such as rising ocean temperatures and pollution, which are exacerbated by human-induced climate change. Warmer waters near nuclear plant discharge outlets can attract jellyfish, and their resilience in low-oxygen environments allows them to proliferate where other marine species struggle.
The financial impact of such shutdowns can be significant. For instance, a previous jellyfish-induced shutdown at Scotland’s Torness plant in 2011 cost an estimated $1.5 million per day due to lost power generation. While specific financial details for the Gravelines incident are not provided, the temporary loss of four reactors likely resulted in substantial costs for EDF, both in terms of halted production and the resources required to clear the jellyfish and restart the reactors.
To address such incidents, nuclear plants typically employ measures like debris screens to prevent marine life from entering cooling systems, but these can be overwhelmed during large jellyfish blooms. In response to recurring issues, scientists and engineers are exploring innovative solutions. For example, researchers at Cranfield University in the UK are developing drone-based early warning systems to detect jellyfish swarms before they reach critical infrastructure. These drones can monitor jellyfish locations, numbers, and density, allowing plant operators to adjust cooling mechanisms proactively. Additionally, studies are investigating acoustic detection methods, using the unique “echo energy” or “acoustic scatterings” produced by jellyfish to identify their presence and mitigate risks.
The Gravelines shutdown highlights the broader challenge of managing nuclear power plants in coastal environments, where marine life can pose unexpected operational risks. It also underscores the need for adaptive strategies to address the growing frequency of jellyfish blooms, driven by environmental changes. EDF and other operators may need to invest further in advanced monitoring technologies and infrastructure upgrades to ensure the reliability of nuclear power generation in the face of such natural disruptions.