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The French nuclear reactor that was damaged by jellyfish will face a delayed restart

EDF data revealed on Tuesday that four reactors of France's Gravelines Nuclear Plant will be back in operation this week, a little later than originally planned. They were shut down by a jellyfish swarm in the cooling system.

The plant is located in northern France and is the largest of its kind in the country. It is cooled by a canal that connects to the North Sea. The six units each produce 900 Megawatts, totaling 5.4 Gigawatts.

EDF data indicated that the first reactor, Unit 6, will be restarted on Tuesday. Each day, one reactor should return to service until all four are back in operation on Friday.

The original plan called for all four of them to start on Tuesday.

EDF has not given a reason as to why the delay occurred, despite the fact that France is experiencing a heatwave which is causing many cooling systems for nuclear power plants to have problems.

Data showed that the first reactor was still not running at 1250 GMT, Tuesday.

EDF announced that the entire Gravelines plant had been temporarily shut down on Monday, after a swarm "massive and unpredictable" of jellyfish entered the cooling system. Four reactors have been taken offline while the two others were undergoing maintenance.

The jellyfish was an English Barrel, a native species which is non-stinging and can grow to 90 centimetres in diameter, according to Aaron Fabrice de Kisangani, a citizen scientist.

Aaron explained that the current would have pulled the jellyfish out of the harbour, into the canal, and towards the nuclear power plant. They would then have been trapped by the water cooling system's suction, which would have drawn them into the filters.

He noted that the mild winter and autumn of this year may have caused a larger bloom of jellyfish.

It is not the first instance that jellyfish has disrupted nuclear power plants. In 2011, Scotland's Torness nuclear plant faced similar issues, while Gravelines was also affected in 1993.

Scientists warn that such events may become more frequent due to global warming, the introduction of invasive species and habitat loss for predators. Reporting by Forrest Crillin. Mark Potter (Editing)

(source: Reuters)