This summer, in five European countries, Finland, France, Germany, Sweden and Switzerland, nuclear reactors have had to be put on reduced power or shut down completely because their cooling water got too hot. Nuclear stations use an enormous amount of cooling water, dumping it back into rivers, lakes or the sea, when it has done its work – much warmer than when it was extracted. Problems occurred this summer when the water intake was too warm to cool the plant, and the hot water being returned to the river or sea was killing fish and other wildlife. This problem has occurred in French rivers before, but this year the Baltic Sea was too warm to cool stations in Finland and Sweden. UK’s operating nuclear stations are on colder seas where the threat is more from winter storm damage and rising sea levels.
— source theguardian.com 7 Sep 2018