2.2 Nuclear Pressure Equipment 2.2.1 Design and manufacturing of Nuclear Pressure Equipment The manufacturer of the Nuclear Pressure Equipment (NPE) is responsible for the conformity of this equipment with the applicable safety requirements in order to guarantee that there will be no failures during its operation. These requirements are defined by a European Pressure Equipment (PE) Directive and are supplemented by specific NPE requirements, which take account of their importance for the safety of the installation. The manufacturer defines and applies the rules that enable it to prove compliance with these requirements. As of 2015, the industrial firms, EDF and Framatome in particular, took fundamental measures to change their rules and bring them into line with the regulatory requirements. Most of these actions were carried out within the framework of the “NPE programme” of the French Association for Nuclear Steam Supply System Design (NSSS), Construction and Monitoring Rules (AFCEN), which involves the majority of the profession. The work done, led to the AFCEN issuing methodology guides and several revisions of the RCC-M code (design and construction rules for mechanical equipment of PWR nuclear islands), on which ASN issues a position statement. The work to update the RCC-M will continue beyond 2022. It shall enable this code and the associated guides to be kept up to date according to progress in techniques and practices, and to OEF. ASN asked that AFCEN’s 2019-2022 programme address the methodology for managing deviations and the OEF acquired with regard to welding. A methodology guide was thus drafted, which in particular promotes the principle of the priority given to restoring conformity or repair, rather than keeping as-is. This principle, supported by ASN, was regularly recalled during the recent events, in particular with regard to the main steam line welds on the Flamanville EPR reactor. This guide also highlights good practices in terms of reporting of deviations and taking account of OEF with a view to ensuring continuous improvement. With regard to welding, the discussions in 2022 concerned the work still to be done and tangible assimilation of OEF for the EPR2 project. 2.2.2 Assessment of the design and manufacturing of Nuclear Pressure Equipment ASN assesses the regulatory compliance of the NPEs most important for safety, referred to as “level N1”, corresponding to the reactor pressure vessel, the SGs, the pressuriser, the reactor coolant pumps, the piping, notably that of the Main Primary (MPS) and Secondary (MSS) Systems, as well as the safety valves. This conformity assessment concerns the equipment intended for the new nuclear facilities (more than 200 equipment items are concerned on the Flamanville EPR reactor) and the spare equipment intended for nuclear facilities already in service (notably the replacement SGs). ASN can be assisted in this task by organisations that it approves. These latter can be mandated by ASN with performance of some of the inspections on the “level N1” equipment and are tasked with assessing the regulatory compliance of the NPE less important for safety, said to be “level N2 or N3”. The oversight by ASN and the approved organisations is carried out at the different stages of the design 1. The purpose of the post-weld heat treatment is to release the residual welding stresses and obtain the appropriate mechanical characteristics. The technical baseline requirements for fabrication sets the required temperature range for this operation according to the materials used. and manufacture of the NPEs. It takes the form of an examination of the technical documentation of each equipment item and inspections in the workshops of the manufacturers, as well as at their suppliers and subcontractors. Four organisations or bodies are currently approved by ASN to assess NPE compliance: Apave Exploitation France, Bureau Veritas Exploitation, Vinçotte International and the inspection body of the EDF users. In 2022, with regard to NPE design and manufacture, the approved organisations carried out about 3,700 inspections on the NPE intended for the Flamanville EPR reactor and about 3,500 inspections on the replacement NPE intended for the NPP reactors in operation. These inspections are performed under ASN supervision. With the support of the approved organisations and the Institute for Radiation Protection and Nuclear Safety (IRSN), ASN examined all the steps taken by the manufacturers and by EDF to address the problems associated with post-weld heat treatment(1). ASN concluded that these measures, which could in certain cases require strengthened in-service monitoring provisions, ensure that the safety of the equipment concerned by these problems is maintained. In particular, during the investigations carried out by Framatome following the discovery in 2019 of a deviation concerning the use of post-weld heat treatment, a new problem linked to high residual stresses generated during the cooling of these postweld heat treatments was brought to light. This problem was addressed by Framatome and by the other SG manufacturers (Westinghouse and Mitsubishi Heavy Industry) by optimising the use of their processes to reduce the residual stress levels liable to be generated during cooling. Framatome continued its quality improvement actions at its three plants. EDF in particular improved the skills management and deviations prevention and handling processes, by deploying monitoring of the most sensitive industrial processes, such as the welding and heat treatment processes, along with supplier approval, evaluation and surveillance. Through its inspections, ASN evaluates the results of these actions, which apply to the manufacture of spare equipment for the NPPs and to the future manufacture of equipment for the EPR2 reactors. It thus underlines the quality and pertinence of the actions taken, which should lead to improved quality of manufacturing. For several years, ASN has in particular maintained its involvement in monitoring the steps defined to ensure that a long-term, robust and efficient organisation tailored to the safety issues is maintained within the Framatome Le Creusot plant. The manufacturer Westinghouse continued to apply its improvement plan in its SG manufacturing plant in Italy, with regard to the internal quality and monitoring system. The pre-conditions for lifting the reinforced surveillance currently in place were defined and ASN, with the involvement of the organisation it mandated, is examining the progress being made in correcting the significant manufacturing deviations. ASN finds that the approved organisations, the manufacturers and the licensees are developing an organisation and the corresponding resources within their own structures, in order to prevent and detect the risk of fraud. Although progress has been observed, improvements are still needed in the implementation of the technical procedures. ASN Report on the state of nuclear safety and radiation protection in France in 2022 291 • 10 • The EDF Nuclear Power Plants 10 01 07 08 13 AP 04 06 12 14 03 09 05 11 02
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