In April, IRSN - ASN's technical arm - had already recommended that EDF repair the eight weldings, which are hard to reach and hard to repair. EDF had hoped to convince ASN that the flaws in the weldings were not a threat to the reactor's safety and wanted to leave them in place.

The ASN was due to rule on the recommendation this month. Its statement gave no further details.

EDF CEO Jean-Bernard Levy said on Tuesday that repairing the weldings would cause further delays to the reactor, which is already years behind schedule and billions of euros over budget.

Following the discovery of the problems with the weldings, EDF in July 2018 delayed the scheduled loading of nuclear fuel by a year to the fourth quarter of 2019.

(Reporting by Geert De Clercq; Editing by Leigh Thomas)