PARIS — At least five nuclear reactors operated by French utility EDF might have problems with weldings on their steam generators, a fault which has raised fears of closures, France's nuclear regulator was quoted as saying.

State-controlled EDF, whose shares were down 0.9% on Thursday, had said on Tuesday it had identified issues with weldings of some existing reactors, sparking a stock price fall of nearly 7%.

France has the world's second-largest fleet of nuclear reactors behind the United States, but a spate of technical problems, coupled with hitches at reactors under construction, has tarnished EDF's image as a leader in nuclear technology.

EDF has exported to China, Finland, South Africa and South Korea, with Britain also set to use its equipment.

"At least five nuclear reactors are affected by this problem," Le Figaro newspaper quoted Bernard Doroszczuk, head of the ASN regulator, as saying.

"EDF has advised that in around a week it will give an exact number of facilities affected," Doroszczuk added.

A spokesman for EDF said that there was no plan to shut down the reactors involved for the time being, but the situation could change and it would be for ASN to decide.

"We are carrying out an in-depth investigation of every part in the reactors that could be impacted by the issue. Based on the investigation, we will determine the remedial options."

Reactor closures, if they were to happen ahead of winter when power consumption rises, would impact power generation in France, which depends heavily on nuclear power, and, potentially in European countries that import electricity from France.

French and the wider European forward power prices firmed in wholesale trade on concerns over French nuclear availability, while gains in carbon emissions permit and gas prices provided support, a London-based trader said.

France's baseload electricity contract for year-ahead delivery rose 0.4% to 53.75 euros a megawatt hour (MWh). The contract hit an eight-week high of 55.25 euros/MWh on Wednesday.

French December delivery power contract surged 11 percent or 7 euros to 70 euros/MWh. Germany's year-ahead delivery price, the European benchmark power contract added 0.4% to 50.40 euros/MWh.

On Wednesday, the ASN said it had put EDF's Flamanville 1 and 2 reactors under increased surveillance following a series of shortcomings in maintenance and contractor oversight. — Reuters