EDF wrote in a press release, "preventive maintenance checks on the primary circuit of reactor number 1 of the Civaux Nuclear Power Plant" found cracks due to corrosion on the pipes.
"Checks initiated on the same equipment of reactor number 2 of the Civaux Nuclear Power Plant revealed similar defects," the French power giant said.
France's Nuclear Safety Authority (ASN) was informed about cracks detected close to the welds on the reactor's pipes.
EDF temporarily closed Civaux to "replace the affected parts on the two Civaux reactors, the work being governed by a technical instruction prepared in cooperation with the ASN, which leads to extend the shutdown of the two reactors," it said.
EDF has also chosen to close two reactors at another nuclear plant at Chooz in the northeastern Ardennes department for inspections. Both power plants use the same reactor technology.
The temporarily closing of Civaux's reactors and Chooz's reactors will reduce one terawatt-hour of output and couldn't come at the worst time as cooler weather sent French power contracts to a record high earlier this week.
A power reduction could suggest strain on the power grid amid cooler weather and higher power prices.