France, June 26 -- EDF, France's electricity operator, shut down one reactor at its Golfech nuclear plant on the Garonne on Monday after river temperatures approached the site's operating limit of 28C. Output has also been reduced at reactors in Bugey on the Rhone and Nogent-sur-Seine.

The disruption remains limited. France's grid operator RTE said electricity supplies remain secure. EDF said the loss of 2.2 gigawatts - about 3.5 percent of the country's nuclear capacity - does not threaten the balance between supply and demand.

But ecologists and some energy experts say the shutdowns are part of a growing pattern that raises questions about how a nuclear fleet largely designed in the 1970s will cope with a warming planet.

Drought and ...