* Report says carbon concentrations no threat to reactor safety
* EDF will have to monitor Flamanville reactor over its lifespan
* Non-approval would have been major setback for EDF, Areva
* ASN to give final ruling on reactor in the autumn (Adds detail on vessel investigation, timing for ruling)
By Geert De Clercq
PARIS, June 23 (Reuters) - A long-awaited report on the safety of the nuclear reactor EDF is building in Flamanville, north-western France, declares the reactor vessel fit for purpose, two sources with direct knowledge of the report told Reuters on Friday.
A negative report from the IRSN, the technical arm of French nuclear regulator ASN, would have been a major setback for EDF, costing billions of euros and years of delays as the reactor vessel is welded in place and the reactor dome was sealed in 2013.
Its safety was under scrutiny because of excessive carbon concentrations - which can make steel brittle - in its lid and cover. But the report says the reactor will be able to operate safely, although it will need extra monitoring over its lifetime.
A favourable ruling by the nuclear safety authority is also a European Commission condition for its approval of EDF’s takeover of state-owned Areva’s reactor unit, which has designed the Flamanville European Pressurised Reactor (EPR). EDF also plans to build two EPRs in Hinkley Point, Britain.
A group of independent nuclear experts, who received the report last week, will discuss the 180-page document on Monday and Tuesday to formulate an opinion. The ASN has said it will make the report public following the experts’ meeting.
Based on the IRSN report and the experts’ input, the ASN will draft a provisional ruling - expected in July - about the reactor which it will submit for public consultation until September. Once that consultation over, it will issue a binding ruling on whether the reactor can start up as scheduled in 2018.
Industry experts say it is unlikely that the ASN would deviate far from the IRSN report, as no new technical investigations will be done.
In an interview with Les Echos newspaper early this month, EDF’s CEO Jean-Bernard Levy had said that he was “more confident than ever” that the ASN would clear the safety of the vessel.
Early 2015, when the carbon concentrations were discovered, ASN director Pierre-Franck Chevet said these represented a very serious anomaly as they affect a crucial reactor component on which no risk of rupture can be taken.
A source familiar with the ASN report said that while carbon concentrations of about 0.30 percent in some areas were above the regulatory maximum of 0.22 percent, the deviation was not of a nature to threaten the integrity of the reactor in case of physical or thermal shocks.
The source added that the excess carbon concentrations are only present in the base and cover of the vessel, made by Areva-owned foundry Creusot Forge, but not in the vessel’s hull, which is more exposed to radiation than the base and cover.
France’s anti-nuclear organisations have repeatedly called on the ASN not to approve Flamanville.
“Under pressure from EDF and Areva ... the nuclear watchdog is getting ready to give the green light for this defective piece of equipment which does not meet safety criteria,” Sortir du Nucleaire action group said in a statement early this month.
Reporting by Geert De Clercq; Editing by Dale Hudson and Elaine Hardcastle