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The spineless foe of nuclear power plants: How jellyfish disrupt these facilities

Since at least the 1990s, nuclear power plants across the world have been forced to shut down due to jellyfish getting clogged in their cooling system. Such incidents are now on the rise as climate change and marine pollution have increased the jellyfish population.

in 2011 alone, jellyfish paralysed plants in Israel, Japan, and Scotland. (Photo: Wikimedia Commons)

5 min readNew DelhiAug 13, 2025 05:07 PM IST First published on: Aug 13, 2025 at 05:07 PM IST

One of the largest nuclear power plants in France was forced to temporarily shut down on Sunday (August 10) due to a slimy and spineless adversary: jellyfish.

The incident took place after a “massive and unpredictable” swarm of the marine creature clogged up the plant’s cooling system. It led three of the six reactors at the Gravelines Nuclear Power Station in Northern France to go offline, according to the French nuclear company EDF, which operates the plant. A fourth reactor shut down on Monday.

EDF said that jellyfish “had no impact on the safety of the facilities, the safety of personnel, or the environment”.

This is not the first time that jellyfish have thwarted nuclear plants. Swarms of these invertibrates have caused such disruptions across the world since at least the 1990s — Gravelines itself was disrupted in 1993.

However, experts suggest that the incidents of jellyfish disrupting power generation have been on the rise in recent years. For instance, in 2011 alone, jellyfish paralysed plants in Israel, Japan, and Scotland. In 2013, an invasion of jellyfish halted a reactor in Sweden.

How do jellyfish thwart nuclear plants?

Nuclear power plants require a constant flow of water to cool their reactors and turbine systems, which is why many plants are typically built near large bodies of water. The plants’ intake pipes have screening areas that have grated barrier systems to remove solid materials and aquatic life, and allow the inflow of water, sometimes millions of gallons every minute.

However, jellyfish pose a unique problem to this system. When a large volume of jellyfish — around a million individuals — gets pulled in by the intake pipes, they entirely cover and clog the screening areas within minutes. As a result, the flow of water is interrupted. This risks overheating and damage to the major plant constituents, such as the turbines, condensers, and boilers, forcing the reactors to shut down.

Such a large number of jellyfish are typically pulled in when these creatures bloom — a rapid, temporary increase in jellyfish reproduction rates — near coastal nuclear power plants. During this process, millions of separate jellyfish clump together into dense groups.

Another issue is that dead jellyfish can turn into a gel and pass through the screens, causing problems deeper in the plant system.

Removing jellyfish from the screens involves complicated and dangerous procedures. If a large population of jellyfish has clogged the intake pipes, it may take up to two days for the workers to clean them (‘Preventing Jellyfish Attacks on Electrical Power Plants in Kuwait: An Innovative Solution’, The International Journal of Engineering and Science, 2024). During this process, there is a chance that jellyfish may sting the workers.

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Why are such incidents on the rise?

The increase in incidents of power disruption caused by jellyfish is primarily due to a rise in their population in recent years, and their ability to adapt to the conditions found in and around coastal nuclear power plants. Several factors are contributing to the proliferation of jellyfish.

CLIMATE CHANGE: Global warming has led to higher ocean temperatures, which, in turn, has resulted in the surge of plankton — the primary food source of jellyfish. With an abundance of food available, jellyfish have been able to increase their population substantially.

Also, these marine creatures breed faster in warmer water. Studies have found that higher temperatures lead to a higher metabolic rate and faster division of cells among jellyfish.

This is what has been happening in the North Sea, from where the Gravelines Nuclear Power Station gets its cooling water, and several jellyfish species are currently thriving. “Because areas like the North Sea are becoming warmer, the reproductive window is getting wider and wider,” Derek Wright, marine biology consultant with the United States National Oceanic and Atmospheric Administration (NOAA), told Reuters.

OVERFISHING: Jellyfish have proliferated because of overfishing as well. That’s because various kinds of species, such as tuna and sea turtles, that prey on them have been removed from the ecosystem. These species also feed on plankton, and with their reduced population, jellyfish have more plankton to consume and thrive unchecked.

PLASTIC POLLUTION: Unlike other marine creatures, jellyfish can tolerate low oxygen levels in water, which is a consequence of pollution. This has also contributed to the increase in their population in recent years.

Moreover, plastic waste of just a few centimetres can serve as a breeding colony for jellyfish. This brings them close to coastlines and reproduce. The process increases the risk of jellyfish getting pulled in by the plants’ intake pipes, especially during blooms.

As global temperatures continue to soar and marine ecosystems further deteriorate, the population of jellyfish is expected to skyrocket. This would increase the number of nuclear power plant shutdowns due to jellyfish, resulting in power disruption and loss of millions of dollars.