PARIS (Reuters) - Problems with weldings have forced French utility EDF EDF.PA to delay the start-up date for its troubled Flamanville 3 nuclear reactor to the second quarter of 2020 and pushed its cost estimate up to three times the original budget.

FILE PHOTO: A general view of the construction site of the third-generation European Pressurised Water nuclear reactor (EPR) in Flamanville, France, November 16, 2016. REUTERS/Benoit Tessier/File Photo

When construction started in 2007, the target launch date was 2012, but the project has suffered a string of serious technical problems - including the discovery of weak spots in its reactor vessel cover - and has been delayed several times.

The cost estimate is now up by another 400 million euros to 10.9 billion euros ($12.75 billion), EDF said in a statement.

It said that loading of the nuclear fuel, last set for the fourth quarter of 2018, was now scheduled for the fourth quarter of 2019.

On a call with reporters, Flamanville project director Laurent Thieffry said that repairs to the weldings would start at the end of this month and continue till summer 2019.

He added that the reactor would be connected to the grid in the first quarter of 2020 and its commercial start at full power was now scheduled for the second quarter of 2020.

“The new planning for the EPR reactor in Flamanville is totally realistic,” EDF head of new nuclear projects Xavier Ursat said. But he added that the startup schedule would depend on the go-ahead of nuclear regulator ASN.

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EDF said the 400 million euro extra cost consisted of 60 to 70 million euros in cost directly related to the welding repairs, with the rest due to the impact of the delay on the entire project.

EDF shares were down 0.9 percent in early trading on a virtually flat French bourse.

WELDINGS

The utility said a total of 53 weldings on the reactor’s secondary circuit would have to be redone, while for another 10 it is confident that it can convince regulator ASN that they are fit for service. Another 85 weldings were in line with specifications and needed no repairs, it said.

The secondary circuit consists of 360 meters of 50-95 cm diameter piping that conducts steam from the reactor’s four steam generators to the plant’s turbine, and pumps condensed water back to the steam generators.

Four to five centimeters thick, the pipes require high-tech welding that needs to go around each pipe 100 times and takes eight weeks per welding.

EDF said the 400 million euro extra cost consisted of 60 to 70 million euros directly related to the welding repairs, with the rest due to the impact of the delay on the entire project.

EDF said it would closely supervise and control the welding work on the reactor itself. A parliament report about nuclear security released this month said that excessive reliance on outsourcing was causing safety issues in EDF’s reactors.

France relies on nuclear energy for 75 percent of its electricity. The EPR reactor is the first new reactor to be built on its soil in decades.

The French government wants to reduce the country’s reliance on nuclear to 50 percent and will decide later this year by when this target should be reached.