The news about additional stress corrosion, which according to the watchdog occurred in a part of the reactor which EDF had not considered prone to stress corrosion, comes after five months of intensive repair works at the site.
An EDF spokesperson told Reuters it was still the utility's aim to re-start the reactor in early May.
The company, one of the world’s biggest utilities, last year faced an unprecedented number of outages due to a delayed maintenance schedule and stress corrosion, reducing nuclear production to 30-year lows.
EDF in December had to further delay the restart of several of its reactors hit by stress corrosion, including the Penly 2 reactor located at the same site.
