* EDF shares fall, among worst performers on Paris market
* Major further Flamanville delay could impact EDF earnings (Adds detail and background)
PARIS, April 10 (Reuters) - French state-controlled utility EDF on Tuesday no longer ruled out that problems with weldings at the nuclear reactor under construction in Flamanville may impact the cost and start-up schedule of the reactor.
When EDF first reported those problems on Feb. 22, it had initially said there would be no impact on safety, costs or the reactor start-up schedule.
However, France's ASN nuclear regulator subsequently warned on Feb. 28 that the substandard weldings could well have an impact on the Flamanville startup calendar.
"Following the current checks and the licensing process by the ASN, EDF will be able to specify whether the project requires an adjustment to its timetable and its costs," EDF said in a statement about the Flamanville site in northern France.
EDF shares were down 1.5 percent in early session trading, among the worst performers on the broader Paris SBF-120 index , which was up 0.5 percent.
Any major further delay to the EPR reactor in Flamanville - the same type reactor that EDF is building in Hinkley Point, Britain - could add hundreds of millions of euros to the budget and could negatively impact EDF earnings.
Even before the weldings problems were first reported, ASN had already warned several times that the start-up schedule was tight.
The Flamanville reactor is expected to load nuclear fuel at the end of the fourth quarter of 2018.
In 2015, its cost was estimated at 10.5 billion euros ($12.9 billion)- more than three times its original budget - but since then the budget has not been updated, despite the discovery of several additional major problems, notably with weak spots in the steel of the cover of its containment vessel.
On Feb. 22, EDF had said that 38 of 66 weldings on the Flamanville reactor's secondary cooling circuit were not in line with standards aimed at making them rupture-proof, although it said they did meet ASN requirements.
EDF said on Tuesday that following the detection of quality deviations, it had decided to carry out additional controls on 150 weldings on the main secondary system, in order to identify exactly which ones are subject to quality deviations.
It said that following this inspection, it had notified the ASN on April 10 of "a significant event" relating to the deviations in the weldings.
($1 = 0.8114 euros) (Reporting by Geert De Clercq; Editing by Sudip Kar-Gupta)