ASN Report 2020

In accordance with the provisions of Article L. 593-19 of the Environment Code, following this periodic safety review, the licensee sends ASN a periodic safety review concluding report. In this report, the licensee gives its position on the regulatory compliance of its facility as well as on the modifications made to remedy the deviations observed or improve the safety of the facility and, as necessary, proposes implementing additional improvements. The periodic safety review report comprises the parts specified by the Environment Code. ASN analysis The guidelines of the generic programmes proposed by EDF for verification of the status of the facility and reassessment of safety are the subject of an ASN position statement issued following consultation of the GPR and possibly of the GPESPN. On this basis, EDF carries out safety reassessment studies and defines the modifications to be made. Following consultation of the Advisory Committees at the end of the periodic safety review generic phase, ASN issues a position statement on the results of the reassessment studies and on the modifications to allow the safety improvements envisaged by EDF. ASN then informs the Minister responsible for nuclear safety of its analysis of the review concluding report for each nuclear power reactor, mentioned in Article L. 593-19 of the Environment Code, and may issue new binding requirements regarding its continued operation. The Energy Transition for Green Growth Act 2015-992 of 17 August 2015 supplemented the framework applicable to the periodic safety reviews on nuclear power reactors. It more specifically requires ASN authorisation, following a public inquiry, of the provisions proposed by the licensee during the periodic safety reviews beyond the 35th year of operation of a nuclear power reactor. Five years after submitting the periodic safety review report, the licensee also submits an interim report on the condition of the equipment, in the light of which ASN may supplement its binding requirements. The main challenges in managing ageing As with all industrial facilities, NPPs are subject to ageing. ASN ensures that, in line with its general operating and maintenance strategy, EDF takes account of ageing-related phenomena in order to maintain a satisfactory level of safety in the installations for their operating lifetime. To understand the ageing of an NPP, over and above simply the time that has passed since it was commissioned, a certain number of factors must be considered, more specifically the existence of physical phenomena which can degrade the characteristics of the equipment according to its usage or its conditions of use. Deterioration of replaceable items Equipment ageing is the result of phenomena such as the hardening of certain steels under the effect of irradiation or temperature, the swelling of certain concretes, hardening of polymers, corrosion of metals, etc. This deterioration is generally incorporated as of the design and manufacture of the facilities and then in a programme of monitoring and preventive maintenance, as well as of repair or replacement if necessary. The lifetime of non-replaceable items Non-replaceable items, such as the reactor pressure vessel (see point 2.2) and the containment (see point 2.3), are subject to close monitoring in order to check that they age as anticipated and that their mechanical characteristics remain within the limits allowing satisfactory behaviour. Obsolescence of equipment and its components Before it is installed in the NPPs, some equipment undergoes a qualification process designed to ensure that it is able to perform its functions in the stress and atmosphere conditions corresponding to the accident situations in which it would be required. The availability of spares for this equipment is heavily dependent on any changes in the industrial network of suppliers. The end of manufacturing of certain components or the closure of the manufacturing company can lead to supply difficulties. Prior to their installation, EDF must check that new spares that are different from the original parts do not compromise the qualification of the equipment on which they are to be installed. Given the time required for this procedure, EDF must anticipate well in advance. The nuclear power reactors ageing management process The approach adopted by EDF to manage the ageing of its facilities is built around three key points: ∙ Anticipate ageing as of the design process: at design and during manufacture of the components, the choice of materials and the installation arrangements must be appropriate to the planned operating conditions and take account of the known or presumed degradation kinetics. ∙ Monitor the actual condition of the facility: during operation, degradation phenomena other than those considered in the design can be discovered. The periodic test and preventive maintenance programmes, the additional investigation programmes as well as examination of operating experience feedback (see points 2.4.3, 2.4.4, 2.4.7, 2.4.8 and 2.6.1) must enable these phenomena to be detected sufficiently well in advance. ∙ Repair, renovate or replace the equipment: given the operating constraints that such routine or exceptional maintenance operations are liable to generate, especially when they can only be performed during nuclear power reactor outages, EDF must seek to anticipate them, in particular to take account of the time taken to procure new components, the time taken to prepare for and carry out the work, the risk of obsolescence of components and the loss of technical skills on the part of the workforce. At the request of ASN, EDF established a methodology for managing the ageing of its nuclear power reactors beyond 30 years of operation, the aim of which is to demonstrate their ability to continue to function until their fourth periodic safety review in satisfactory conditions of safety, on the one hand in the light of the understanding of and ability to manage the mechanisms and kinetics of the damage modes linked to ageing and, on the other, according to the condition of the facilities observed during their third periodic safety review. This methodology comprises a first generic phase which aims to determine how ageing is taken into account for a set of similar reactors. Subsequently, on the occasion of the third periodic safety review of each nuclear power reactor, a summary file specific to the reactor is drawn up in order to demonstrate management of the ageing of the equipment and the reactor’s ability to continue to function for the ten-year period following its third ten-yearly inspection. To ensure continued operation of the nuclear power reactors beyond their fourth ten-yearly inspection, EDF reuses this type of approach, which is applied not only to all the systems, structures and components important for managing radiological risks, but also conventional risks. 312 ASN Report on the state of nuclear safety and radiation protection in France in 2020 10 – THE EDF NUCLEAR POWER PLANTS