The French nuclear safety authority (Autorité de Sûreté Nucléaire – ASN) has said that five nuclear power units – Civaux NPP unit 1, Fessenheim NPP unit 1, Gravelines NPP unit 4, and Tricastin NPP units 2 and 4 – should be taken offline for additional inspections on their steam generators (SGs) within the next three months. The steel in some parts of the SGs is thought to contain high levels of carbon, following a review of Areva's Le Creusot facility, where they were manufactured.

The upper and bottom heads of the reactor pressure vessel for the European Pressurised Water Reactor (EPR) under construction at unit 3 of the Flamanville NPP were manufactured Le Creusot in September 2006 and January 2007 and were subsequently found to contain a high carbon content. This prompted Areva to review the company's quality management process in 2015 for some 400 heavy steel components made at the Creusot Forge plant since 1965.

ASN then requested Areva and EDF to identify any other components in operating nuclear power reactors that could be similarly affected. EDF was also asked to justify the mechanical resistance of the SG bottom heads that had been manufactured either at Le Creusot or by Japan Casting and Forging Corporation (JCFC).

In June, the ASN said it had identified 18 EDF reactors (both 900MWe and 1,450MWe), in which the SGs could contain high carbon concentrations.

It noted that 12 of these, equipped with channel heads manufactured by JCFC, were "liable to contain a particularly high carbon concentration". The 900MWe pressurised water reactors (PWRs) each have three steam generators, and the 1,450MWe PWRs each have four.

ASN said EDF had since provided data aimed at demonstrating the operating safety of those 12 reactors but called for additional inspections to verify whether each of the channel heads concerned conformed with the data submitted by EDF. Of the 18 reactors at risk, ASN said six have already been granted approval to restart and are operating normally: Blayais NPP unit 1, Chinon NPP units 1 and 2, Dampierre NPP units  2 and 4, and Saint-Laurent NPP B1.

Seven others are on planned outage and have been or are being inspected: Civaux NPP unit 2, Dampierre NPP unit 3, Gravelines NPP unit 2, Tricastin NPP unit 1, Tricastin NPP unit 3, Saint-Laurent B2 and Bugey NPP unit 4.

However, ASN said inspections at the other five units – Civaux 1, Fessenheim 1, Gravelines 4, and Tricastin 2 and 4 – must be carried out within the next three months "without waiting for the scheduled refuelling outage of these reactors". As the inspections can only be conducted when the reactors are offline, the units will have to be shut down. Tricastin 4 will be taken offline from 22 October to 19 December; Fessenheim 1 from 10 December to 3 January 2017; Gravelines 4 from 17 December to 10 January; Civaux 1 from 23 December to 15 January; and Tricastin 2 from 23 December to 15 January.  

ASN CEO Olivier Gupta told Le Monde newspaper that “the safety margins are very large and the carbon content does not undermine integrity or security, even in the case of an accident”. France has 58 nuclear reactors with total capacity of 63.2GWe which provide some 70% of its total electricity. In April, President Francois Hollande promised to formally initiate the shutdown of the oldest nuclear reactors on the grounds of environmental and safety concerns, including the Fessenheim NPP near the German and Swiss borders, which has been operating since 1978.