Faulty welds at a nuclear power plant under construction in France could delay its opening and push up its ultimate cost.

ASN, the French nuclear regulator, said that state-owned EDF would have to repair eight faulty welds in the Flamanville reactor’s containment building. It rejected a request to delay repairs until 2024, after the plant's expected startup.

The Flamanville nuclear station in France. Source: EDFThe Flamanville nuclear station in France. Source: EDFIn a similar procedure two years ago, ASN ruled that Flamanville could start up despite weak spots in the steel of its reactor vessel cover. The regulator ordered the utility to replace the reactor cover by 2024 at the latest.

According to the news agency Reuters, EDF said in a statement that it is analyzing the impact of the ASN ruling on startup schedule and costs and that it will give an update in the coming weeks.

EDF reportedly said it had estimated it could repair the welds by the end of 2022.

The repairs could delay the reactor's startup by up to three years from the most recent target. The utility had slated fuel loading to take place by the end of 2019. When construction of Flamanville started in 2007, the original target launch date was 2012.

(Read "Quality defects will delay this nuclear unit's startup.")

Welding defects in a system that directs steam produced in the plant's steam generators to its turbine were detected in March 2018 during a required regulatory inspection. The inspection included an examination of the welds in the plant's primary and secondary systems, and sets a baseline condition of the plant before it begins operating.

The utility went on to inspect 150 welds and found that 33 had quality deficiencies that needed to be repaired. Another 20 welds were to be redone, even though they did not have any defects, as they fell short of quality goals set by the utility. For 10 other welds, EDF submitted a proposal to regulators detailing a specific justification method to ensure safety through the plant's operating life. The remaining 85 welds were said to be compliant, the utility said.

EDF also said last year that the welding problems would add an extra 400 million euros ($452 million) in costs, pushing the total cost of the project up to 10.9 billion euros ($12.34 billion), compared to an initial estimate of 3 billion euros ($3.4 billion).