Situation of the steam generators in which the steel contains a high carbon concentration: ASN considers that restart of the reactors concerned can be envisaged. Specific checks on each reactor remain necessary.

With the support of IRSN, ASN examined the information transmitted by EDF to demonstrate the serviceability of the channel heads on the steam generators¹ manufactured by JCFC² and equipping ten 900 MWe reactors and two 1450 MWe reactors.

ASN considers that provided that its requests are taken into account, the generic demonstrations provided by EDF are acceptable for the 900 MWe reactors and can be used on each of the reactors concerned with a view to ASN authorising their restart. EDF informed ASN that it will shortly be sending its additional data regarding the 1450 MWe reactors.

At ASN’s request, EDF initiated a programme of analyses in 2015 to identify the equipment on its reactors in service which could be affected by a carbon concentration anomaly in the steel used. These analyses concluded that the channel heads in certain steam generators were concerned by this anomaly. This could lead to mechanical properties of the steel that are lower than expected, thus compromising the safety of the reactors, which is based on the preclusion of failure of these components.

In letters on 7^th October and 15^th November 2016, EDF sent ASN a generic file aimed at demonstrating the serviceability of the channel heads on the steam generators manufactured by JCFC and equipping the 900 MWe reactors. They were examined by ASN and IRSN, who verified that the hypotheses and method used were acceptable. The hypotheses of the EDF file will however need to be confirmed by a test programme on representative scale-one replicas.

Following this examination, ASN sent EDF requests concerning the additional inspections required, the compensatory operational measures to be implemented or reinforced and the additional tests or studies to be performed in the medium term. ASN approval is also required for each reactor restart on the basis of a specific file.

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List of 900 MWe reactors equipped with steam generator channel heads manufactured by JCFC:

• Bugey NPP, reactor 4
• Dampierre NPP, reactor 3
• Fessenheim NPP, reactor 1
• Gravelines NPP, reactors 2 and 4
• Saint-Laurent-des-Eaux NPP, reactor B1
• Tricastin NPP, reactors 1, 2, 3 and 4

List of 1450 MWe reactors equipped with steam generator channel heads manufactured by JCFC:

• Civaux NPP, reactors 1 and 2

On 7^th 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, which are the subject of this press release;
• 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.