In addition, the detection of a rising neutron flux phenomenon at the bottom and top of the fissile column of MOX fuel assemblies led ASN in 2018 to ask the licensee to adopt compensatory measures in 2018, pending the deployment of changes to the design of these assemblies. These particular operating measures have been in place since 2020, pending complete replacement of the MOX fuel assemblies present in the reactors by modified assemblies. The MOX assemblies loaded into the core since 2021 are equipped with a new shim designed to attenuate the rising flux phenomenon at the bottom of the fissile column. EDF will propose an optimised design in 2022, which will be deployed in full in 2025. EDF is also working on a modification for the top of the fissile column of rods. In 2021, the production difficulties encountered at the Melox plant led EDF to use numerous specific refuelling loads in its reactors. In 2021, ASN notably authorised three or four consecutive reloads with no new MOX type fuel assemblies. 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 also take account of their importance for the safety of the installation. The manufacturer defines and applies the rules enabling it to demonstrate 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 French Association for Nuclear Steam Supply System Design (NSSS), Construction and Monitoring Rules (AFCEN), which involves the majority of the profession. This approach was repeated for the years 2019 to 2022, so that the profession continues to make progress on certain topics and in order to learn the lessons from the initial applications of the guidelines and methods created and the deviations observed during manufacturing. The Framatome Le Creusot plant gradually resumed operations in 2021, with the manufacture of several shells intended for the SG replacement programme. During the investigations carried out by Framatome following the discovery in 2019 of a deviation concerning the use of postweld heat treatment, the manufacturer found a new problem in 2021 linked to high residual stresses generated during the cooling of this stress-relieving heat treatments (see box above). 2.2.2 Assessment of the design and manufacturing of Nuclear Pressure Equipment ASN assesses the regulatory compliance of the NPEs most im– portant 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 NPEs 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 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 inspection organisations or bodies are currently approved by ASN to assess NPEs compliance: Apave SA, Bureau Veritas Exploitation, Vinçotte International and the inspection body of the EDF users. In 2021, with regard to NPEs design and manufacture, the approved organisations carried out about 3,100 inspections on the NPEs intended for the Flamanville EPR and about 4,700 inspections on the replacement NPE intended for the NPP reactors in operation. These inspections are performed under ASN supervision. ASN notes the steps taken by industry to deal with the problems identified in its findings, as well as the appropriate nature of AFCEN’s publications. ASN asked that AFCEN’s 20192022 programme address the management of deviations and OEF acquired with regard to welding. With the involvement of the approved organisations and IRSN, ASN examined the programme of work implemented by Framatome to characterise the impact of the residual stresses generated during stress-relieving heat treatment. Provisions regarding the in-service monitoring of the equipment could be needed to ensure that the level of equipment safety is maintained. ASN also asked the other manufacturers to evaluate this impact and is examining the steps they are taking. Framatome continued its quality improvement actions at its three plants. This entails an approach to closely monitor the most sensitive industrial processes affected by significant deviations. Through its inspections, ASN assesses the results of these actions. It thus underlines the quality and pertinence of the steps taken, which should lead to improved production quality. ASN 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 Creusot plant. The manufacturer Westinghouse continued to apply its im– provement plan in its SG manufacturing plant in Italy, with regard to the internal monitoring quality system. The conditions for lifting of reinforced monitoring were defined but were not met in 2021. 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. Even though progress has been observed, the technical measures implemented still need to be improved, as in 2020. The processing of the irregularities reported at the end of 2018 by the supplier of special alloys and steels, Aubert & Duval, is also continuing. The investigations carried out have not yet identified any consequences for the safety of the facilities. 2.2.3 Pressure Equipment operation The reactor Main Primary and Secondary Systems (MPS and MSS), which contribute to the containment of the radioactive substances, to cooling and to controlling reactivity, operate at high temperature and high pressure. The monitoring of the operation of these systems is regulated by the Order of 10 November 1999 relative to the monitoring ASN Report on the state of nuclear safety and radiation protection in France in 2021 285 10 – THE EDF NUCLEAR POWER PLANTS 08 07 13 04 10 06 12 14 03 09 05 11 02 AP 01
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