Two of the Gravelines plant's six reactors had to be taken out of service on Wednesday and Thursday because of jellyfish in the cooling water system, the French operator EDF announced, according to the BBC.
The same situation affected Gravelines earlier this summer, as well as last year.
This comes at a time when French and European nuclear power is already under pressure from heatwaves and drought, with reactors in a number of countries shut down as a result.
