France decided after the 1970s oil crises to rapidly expand its nuclear power capacity in order to build up reliable energy supplies, and has long exported power to its neighbours.

But ever-rising demand for electricity combined with ageing nuclear reactors have brought that policy under increasing scrutiny.

A third of France's 58 nuclear reactors were down and one was operating at 60 percent capacity at the start of November, according to an AFP survey.

A strike at the EDF power firm earlier this year delayed the annual programme to replace fuel rods at the plants, causing a backlog that resulted in output being reduced for several months to come, industry executives said.

And drought this summer lowered water levels in dams and further decreased electricity production, EDF said.

The power grid operator RTE said this month that suppliers might be forced to ask big industrial clients to ration power use and warned it could even resort to rolling power cuts in some regions.

Poorly-supplied Brittany in the northwest and the Nice region on the Cote d'Azur would likely be the worst hit, RTE said.

The grid operator said this week that electricity production was at such a reduced level that in October, for the first time since 1982, France had to import 458 gigawatt hours from Germany, Britain and Switzerland.

"Selling the idea of energy autonomy was commercial dressing for the nuclear lobby," said an expert on France's nuclear industry, who asked not to be named.

The real problem today, he said, is "the lack of investment, particularly in personnel, in nuclear installations."

"We were assured that (nuclear) power stations with a lifespan of 30 to 40 years could last 60 years. Today, that is posing a problem in terms of supply security," he said.