AmiMoJo quotes Reuters:
Scorching temperatures across Europe coupled with prolonged dry weather has reduced French nuclear power generation by around 5.2 gigawatts (GW) or 8%, French power grid operator RTE’s data showed on Thursday. Electricity output was curtailed at six reactors by 0840 GMT on Thursday, while two other reactors were offline, data showed. High water temperatures and sluggish flows limit the ability to use river water to cool reactors.
In Germany, PreussenElektra, the nuclear unit of utility E.ON, said it would take its Grohnde reactor offline on Friday due to high temperatures in the Weser river.
France’s nuclear reactors supply more than 75% of its electricity, according to the article — though their grid operator says they still have enough capacity left to meet demand.