ASN Report 2017

366 ASN report on the state of nuclear safety and radiation protection in France in 2017 Chapter 12  - EDF Nuclear Power Plants modifications made to remedy deviations observed or to improve the safety of the facility. The review report contains elements stipulated in Article 24 of Decree of 2nd November 2007. The ASN analysis The guidelines of the generic programmes proposed by EDF to verify the status of the facility and reassess safety are the subject of an ASN position statement issued following consultation of the GPR and possibly of the Advisory Committee for Nuclear Pressure Equipment (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 envisaged by EDF that aim to improve safety. ASN informs the Minister responsible for Nuclear Safety of its analysis of the review conclusions report for each nuclear power reactor, mentioned in Article L. 593-19 of the Environment Code and can issue new binding requirements regarding its continued operation. The Energy Transition for Green Growth Act 2015-992 of 17th 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 thirty-fifth 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 these equipment items, in the light of which ASN may supplement its requirements. The main challenges in managing ageing Like all industrial facilities, nuclear power plants 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 and manage the ageing of an NPP, apart from simply the time elapsed since its start-up, a certain number of factors must be taken into account, in particular the existence of physical phenomena that can degrade the characteristics of the equipment, depending on its function or 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, the hardening of polymers, corrosion of metals and so on. These degradations are generally considered at the design and manufacturing stages and then in a monitoring and preventive maintenance programme, or even a repair or replacement programme as necessary. The lifetime of non-replaceable items Non-replaceable items such as the reactor vessel (see point 2.2) and the containment (see point 2.3) are closely monitored in order to ensure that they are ageing as anticipated and that their mechanical properties remain within limits allowing their satisfactory behaviour. Equipment or component obsolescence 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 changes in the industrial network of suppliers, with the cessation of manufacture of certain components or the closure of the manufacturing company, potentially leading to supply difficulties. Prior to installing these parts, EDF must check that the 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 length of this procedure, the licensee must anticipate these needs well in advance. The nuclear power reactors ageing management process The approach adopted by EDF to manage the ageing of its facilities is based on three key points: ཛྷ ཛྷ Anticipate ageing in the design: in the design and during manufacture of components, the choice of materials and the installation arrangements must be tailored to the intended operating conditions and take into account the kinetics of known or presumed deterioration processes. ཛྷ ཛྷ Monitor the actual condition of the facility: during operation, degradation phenomena other than those considered in the design can be discovered. The periodic monitoring 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) are all designed to detect these phenomena sufficiently early. ཛྷ ཛྷ Repair, renovate or replace equipment: given the operating constraints liable to be generated by such routine or exceptional maintenance operations, especially when they can only be performed during NPP reactor outages, EDF must seek to anticipate them, to take account of the time needed to procure new components, the time required to prepare for and carry out the work, the risk of obsolescence of certain 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 after 30 years of operation, the aim of which is to demonstrate their ability to continue to function until their fourth ten- yearly outage inspection 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 during their Third Ten-yearly Outage inspections (VD3).