EDF's flagship nuclear plant may need more repairs to its faulty weldings than originally planned, the French regulator ASN has warned.
The nuclear watchdog said EDF would have to review materials at its Flamanville plant in Normandy.
The state-backed energy company was forced to delay the start-up date for its Flamanville 3 reactor to the second quarter of 2020 – and push its cost up to three times its budget – after discovering that 53 weldings would have to be redone in July.
EDF also said another 10 needed to be tested by the ASN but it was “confident” they were fit for service.
But the regulator said major tests were needed to verify whether eight of those 10 were fit for service and launched an investigation into how the company has handled the welding problems.
It said: “The ASN considers that the problems with the weldings show that EDF has failed to properly oversee certain activities on the Flamanville reactor construction site.”
It added that given problems were initially identified in 2015, EDF's management of the situation had been “inadequate”.
The energy firm is also building two similar reactors at Hinkley Point, in Somerset.