NOTABLE EVENTS 2023 In this opinion, which does not pre-empt the position that ASN will adopt on the occasion of their fifth periodic safety review, regarding the conditions for continued operation of the reactors beyond 50 years, ASN identifies two subjects requiring priority analysis by EDF: • the mechanical strength of certain portions of the primary system main lines of several reactors, called “E elbows” (see opposite); • for the reactors of the Cruas-Meysse Nuclear Power Plant (NPP), taking account of the lessons learned from the earthquake that occurred in Le Teil on 11 November 2019 (see box below). In addition to these two technical subjects, other factors such as considering the expected effects of climate change, or the functioning of the “fuel cycle” facilities in satisfactory conditions of safety, must also be given particular attention with a view to possible operation up to 60 years. Finally, the extensive standardisation of the French NPP fleet, which is a particularity of the French electrical grid, implies the risk of a serious generic defect leading to simultaneous suspension of operation by several reactors, as was recently the case when stress corrosion cracks were discovered on the auxiliary lines of the primary system of several reactors. ASN considers that the possible occurrence of this type of event must be taken into account when checking compliance with security of electricity supply criteria. Position of E elbows on the reactor primary system MECHANICAL STRENGTH OF THE E ELBOWS The E elbows are a part of the main primary systems of the reactors. They are shown in yellow on the figure below. The E elbows for the older reactors (900 and 1,300 Megawatts electric – MWe) are manufactured from cast stainless steel. They are considered by EDF to be very hard to replace, because often located in a zone subjected to levels of irradiation making human intervention difficult. There are particular problems with the steel used in the elbows. On the one hand, the casting process for these elbows is liable to generate manufacturing flaws. On the other, it is subject to a thermal ageing phenomenon. The mechanical strength of the cast elbows on the primary system must thus be demonstrated, taking account of the presence of potential flaws and the reduced tensile strength as a result of ageing. For most of these elbows, EDF demonstrated that their lifetime is greater than 60 years and considers that operation up to 80 years is possible. However, the analyses on the E elbows of five reactors at the time of drafting of the ASN opinion, could not demonstrate continued operation up to 60 years. EDF presented possible avenues to supplement these analyses. ASN considers that the various avenues studied by EDF to operate the elbows up to 60 years are credible, but that they still require work in order to lead to acceptable demonstrations and be implemented. Steam Generator Primary lines E elbow Reactor vessel Reactor coolant pump Lessons learned from the earthquake at Le Teil (Ardèche département) on 11 November 2019 The fault that caused this earthquake led to a surface fracture over several kilometres, with soil uplift and shift of several centimetres. This phenomenon is extremely rare in mainland France. Work is in progress to characterise the scope of the network of faults. If the existence of a fault capable of leading to a surface fracture were to be confirmed under the Cruas-Meysse site, it would then be complicated to produce the safety case for this NPP. It could require significant work, or even compromise the continued operation of its reactors. ABSTRACTS – ASN Report on the state of nuclear safety and radiation protection in France in 2023 17
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