Carbon concentration anomaly in the steel: after inspection, ASN authorised the restart of nine reactors

ASN approved the restart of nine¹ of the twelve reactors concerned by the carbon concentration anomaly in the steam generator channel heads manufactured by JCFC², following its examination of the results of the inspections carried out and the technical demonstrations provided by EDF for the 900 MWe reactors.

On 18^th October 2016, ASN instructed EDF to carry out additional inspections on the steam generator channel heads of certain reactors, within three months.

On 11^th January 2017, EDF asked that the inspection deadline for Tricastin NPP reactor 2 be postponed by two weeks. This request was explained by the risks posed to the electricity grid as a result of the wave of cold weather expected next week. ASN considered this postponement to be acceptable from the safety viewpoint and set the the date of 3rd February 2017 as the inspection deadline for this reactor.

EDF also asked that the inspection deadline set for Civaux NPP reactor 1 be postponed to the end of March 2017. With the assistance of IRSN, ASN is currently examining the substantiating data provided by EDF for the 1450 MWe reactors (Civaux reactors 1 and 2). On this basis, ASN will analyse the conditions for the  restart of reactor 2 - on which the inspections have been carried out - and will shortly issue a position statement on the request for postponement of these inspections on reactor 1.

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On 7th April 2015, ASN made public the discovery of an anomaly in the composition of the steel in certain zones of the vessel closure head and the vessel bottom head of the Flamanville EPR reactor. The detection of this anomaly led ASN to ask Areva NP and EDF to learn all possible lessons from this event. Three processes are currently under way:

• on other components of the EDF reactors, the search for technical anomalies similar to that detected on the Flamanville EPR vessel. This search enabled EDF to identify similar anomalies on the channel heads of certain steam generators;
• manufacturing quality reviews on parts in the Areva NP manufacturing plants, which enabled Areva NP to detect irregularities in the manufacturing files from Creusot Forge;
• initiation of a review of BNI licensee monitoring of their contractors and subcontractors, of ASN oversight and of the alert mechanisms.