Anomaly in the carbon concentration of the steel: after inspection, ASN has authorised restarting of the reactors concerned

Published on 15/03/2017 at 10:00

Information notice

ASN has authorised restarting of the twelve reactors1 concerned by the anomaly in the carbon concentration of the steel of the channel heads of the steam generators manufactured by JCFC2.

On 18th October 2016 ASN had instructed EDF to perform additional inspections of the steam generator channel heads of certain reactors within three months. In view of the results of these inspections and the proof EDF provided regarding the serviceability of these steam generators, ASN authorised restarting of the last reactor concerned - reactor 1 of the Civaux nuclear power plant (NPP) - on 24th February 2017.

Steam generator channel head

ASN has published a chronological record of its exchanges with EDF concerning this anomaly. It has also made the correspondence it sent to EDF available to the public.

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. Detection of this anomaly led ASN to ask Areva NP and EDF to draw all the lessons to be learned from this event. Three processes are currently in progress:

  • the search on other EDF reactor components for technical anomalies similar to those detected on the Flamanville EPR reactor vessel. As a result of this search, EDF has identified similar anomalies on the channel heads of a number of steam generators;
  • reviews of the quality of fabrication of the parts in the Areva NP manufacturing plants which have enabled Areva NP to detect irregularities in the Creusot Forge manufacturing files;
  • the initiation of reflection on the way in which basic nuclear installation licensees monitor their service providers and subcontractors, on ASN oversight and on the alert mechanisms.


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1. Bugey NPP, reactor 4; Civaux NPP, reactors 1 and 2; 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.

2. Japan Casting and Forging Corporation

Date of last update : 03/09/2021