Swarm of jellyfish shuts French nuclear plant

Reuters ^ | 8/11/25 | Forrest Crellin

[DallasBiff]

PARIS, Aug 11 (Reuters) - Four reactors at France's Gravelines nuclear power plant were shut down late Sunday due to a swarm of jellyfish in the cooling systems, operator EDF said on Monday, likely due to rising water temperatures because of global warming. The plant in northern France is one of the largest in the country and cooled from a canal connected to the North Sea. Its six units produce 900 megawatts of power each, or 5.4 gigawatts in total.

[dfwgator]

[dljordan]

“likely due to rising water temperatures because of global warming.”

They just can’t stop.

[subterfuge]

Squid.

[9YearLurker]

I’d think French chefs could make something of them.

[catnipman]

Jellyfish swarms, often called blooms, vary in frequency depending on species, location, and environmental conditions. Blooms typically occur seasonally, driven by factors like water temperature, nutrient availability, and ocean currents. For many species, swarming is most common in warmer months, often spring or summer, when conditions favor reproduction and growth. Some regions see annual blooms, while others experience them irregularly, every few years, or even in rare, massive events triggered by specific conditions like El Niño or climate shifts.

Data is sparse on exact frequencies globally, but studies suggest blooms are increasing in some areas due to warming oceans, overfishing (reducing predators), and nutrient runoff fueling plankton growth, which jellyfish feed on. For example, the Black Sea saw frequent blooms of Mnemiopsis leidyi in the 1980s–90s after its introduction, peaking every few years. In contrast, some coastal areas like the Mediterranean may see smaller, localized swarms multiple times a year.

[so obviously, THIS jellyfish bloom could have been caused ONLY by “global warming”, right reuter’s propagandists?]

[Glad2bnuts]

Obvious question is, now did Jellyfish get into the water? Are they drawing salt water for cooling? As far as I know, jellyfish cannot live in fresh water.

1/3 of all water, uninhabitable.

[GenXPolymath]

Nearly every nuclear plant on a coastline is salt water cooled on the secondary heat exchangers. There is usually a freshwater loop between the ultimate heat sink of the ocean and the comdensers for turbine steam. It’s not a hard engineering issue to do liquid to liquid heat exchangers. Every Navy sub has them, aircraft carrier too.

Backflow doesn’t work at high flow rates since the capacity of the cooling loop is sized to the full output load plus a percentage margin. You would need to double the capacity to pull half off line to backflush the other half. I guess you could do 4 or 8 parallel lines and oversize by 25 or 12.5 percent so you could take 1/4 or 1/8 offline to backflush either way it a continuous OPEX that would only be needed very infrequently.