The Gravelines site in France, which can power around 5 million homes, has temporarily stopped production while teams try to clear the blockage.
Jellyfish have shut down four reactors at France’s largest nuclear power plant.
The swarm entered the filter drums of the pumping stations at the Gravelines site in northern France on Sunday night.
Operator EDF confirmed to Sky News that the «massive and unpredictable presence of jellyfish» caused units 2, 3 and 4 to automatically shut down between 11pm and midnight on 10 August.
Unit 6 then shut down just after 6am on Monday 11 August.
The plant, situated on the coast between Calais and Dunkirk, has six units which can produce a total of 5.4 gigawatts of power.
In a statement, EDF said the pumping stations affected are in the non-nuclear part of the plant, adding the shutdowns «had no impact on the safety of the facility, the safety of personnel or the environment».
