A leak was detected in a pipe downstream of the condenser in the engine room outside the nuclear zone, last week.
An EDF spokeswoman said that the incident did not affect the security of the installations, employees or the environment.
The spokeswoman told Reuters: "Our teams are making a diagnosis. Activity could resume in the coming days."
Meanwhile, the reactor 2 has been closed as part of its planned refueling and maintenance outage.
During the maintenance period, the company will renew a third of the fuel in the reactor and undertake inspection and maintenance work in the facility’s nuclear and non-nuclear parts.
Located on the German border, the France’s oldest nuclear power plant features two reactors, each with a capacity of 900MW.
Commissioned in 1977, the power plant is planned to be decommissioned in 2017 and will be replaced with a new plant, which is set to enter service in the same year in northern France.
