ASN Report 2018

NOTABLE EVENTS 2018 For these pipes, EDF had adopted a «break preclusion» approach, which implies tightened design, manufacturing and in-service monitoring requirements such as to consider that a break of these pipes is extremely improbable. This choice means that the licensee does not study the consequences of a break on these pipes in the facility’s nuclear safety case. In order to achieve the expected high standard of manufacturing quality, the licensee (EDF) and the manufacturer (Framatome) defined tightened requirements, more specifically with respect to the mechanical properties. However, these tightened requirements were not specified to the subcontractor responsible for producing these welds. The inspections carried out during production showed that, for some of these welds, not all of these requirements had been met. In addition, in March 2018, EDF identified a number of flaws during the pre-service inspection of these pipes, as required by the regulations prior to commissioning. These flaws should have been detected by the manufacturer on completion of manufacturing. This finding led EDF to implement a verification programme for all the welds on the main secondary systems, which include the VVP pipes. These new checks revealed flaws requiring repair. ASN verified the performance of these new inspections by EDF. All of these deviations, as well as the ASN findings during its inspections, highlighted a lack of expertise in the welding operations carried out on the VVP pipes and a breakdown in EDF monitoring of its contractors. In July 2018, EDF undertook to restore the required mechanical properties of the welds concerned by the deviations identified, except for the eight welds located in the annulus between the two containments of the reactor building, where access is harder. One of these eight welds also comprises a manufacturing flaw that EDF proposed maintaining as-is. In December 2018, EDF sent ASN a file aiming to demonstrate that the quality of these eight welds is sufficient, enabling their breakage to be precluded with a high level of confidence. This demonstration is more particularly based on an in-depth characterisation of the welds material. ASN’s examination of the EDF file, with the support of IRSN, will continue in 2019. ASN will consult its Advisory Committee for Nuclear Pressure Equipment (GP ESPN) on 9 April 2019 concerning the approach proposed by EDF. In addition, the identification of shortcomings in EDF’s monitoring of its contractors led ASN to ask EDF to conduct a review of the quality of the Flamanville 3 EPR reactor equipment, extended to include a broader scope of equipment and subcontractors, while adapting the depth of the review to the specific implications concerned. Flamanville EPR reactor   Main secondary system pipe welds In brief The welds on the main steam lines in the Flamanville EPR reactor are affected by design and construction deviations. In its letter of 2 October 2018, ASN considered that priority should be given to restoring the conformity of the welds and asked EDF to send it a file presenting its deviations processing approach. This file was examined by ASN, with the technical support of IRSN and their conclusions are presented to the GP ESPNmeeting in April 2019. 1  Steam generators  2  Annulus  3  Feedwater Flow Control System  4  Penetrations  5  Double containment  6  Steam System (VVP) 1 2 1 3 3 4 4 5 5 6 6 A t the beginning of 2017, EDF informed ASN of deviations that had occurred during welding of the main steam lines (VVP system) for the Flamanville EPR reactor. ASN report on the state of nuclear safety and radiation protection in France in 2018  15