* EDF now raises possibility of impact on timing, costs
* Major further Flamanville delay could impact EDF earnings
* EDF review of weldings to be complete by end of May (Adds comments from EDF executives)
PARIS, April 10 (Reuters) - Problems with weldings at a nuclear reactor under construction in Flamanville are worse than first expected and may impact the cost and startup of the long-delayed project, French state-owned utility EDF said on Tuesday.
When EDF first reported weldings problems on Feb. 22, it initially said there would be no impact on safety, costs or the reactor startup schedule.
However, France's ASN nuclear regulator warned on Feb. 28 that the substandard welding could well have an impact on Flamanville's startup. Even before the welding problems emerged, ASN had warned several times the reactor's construction schedule was tight.
"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 site in northern France.
EDF shares fell as much as 2.2 percent in early trading, then recovered to stand one percent lower.
Any major further delay to Flamanville's EPR reactor - the same type EDF is building in Hinkley Point in Britain - could add hundreds of millions of euros to the budget and negatively impact EDF earnings.
The Flamanville 3 reactor is expected to load nuclear fuel at the end of the fourth quarter of 2018. Construction started in 2007 with a launch target of 2012.
After a string of delays, its cost was estimated at 10.5 billion euros ($12.9 billion) in 2015 - more than three times its original budget. Since then the cost has not been updated, despite the discovery of several additional major problems, notably weak spots in the steel of its containment vessel.
On Feb. 22, EDF said 38 of 66 areas of welding on the reactor's secondary cooling circuit were not in line with standards aimed at making them rupture-proof, although it said they still met ASN requirements. https://reut.rs/2H6Km3B
But on Tuesday EDF said additional controls of all 150 weldings on the circuit had shown that some were not in line with ASN requirements.
"Some weldings will have to be redone," said Flamanville director Laurent Thieffry.
EDF head of new nuclear Xavier Ursat said testing and review of the welding will be completed by the end of May, after which EDF will announce any impact on startup timing.
The secondary circuit consists of 360 metres of 50-75 cm diametre 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.
Three-to-four centimetres thick, the pipes require high-tech welding that takes up to eight weeks in each case. Repairs could take up to a few weeks per welding. ($1 = 0.8114 euros) (Reporting by Geert De Clercq; Editing by Sudip Kar-Gupta)