ASN Report 2018

2.10  ̶  NPP operating life extension 2.10.1  –  The age of NPPs The NPPs currently in service in France were built over a relatively short period of time: 45 nuclear power reactors representing nearly 50,000 MWe, or three-quarters of the power output by all French nuclear power reactors, were commissioned between 1980 and 1990, and seven reactors, representing 10,000 MWe, between 1991 and 2000. In December 2018, the average ages of the reactors, calculated from the date of initial reactor criticality, were as follows: ∙ ∙ 37 years for the thirty-four 900 MWe reactors; ∙ ∙ 31 years for the twenty 1,300 MWe reactors; ∙ ∙ 21 years for the four 1,450 MWe reactors. 2.10.2  –  The periodic safety review • The principle of the periodic safety review The periodic safety reviews of nuclear power reactors comprise the following two parts: ∙ ∙ A check on the condition and conformity of the facility: this step aims to evaluate the situation of the facility with respect to the rules applicable to it. It is based on a range of inspections and tests in addition to those performed in real- time. These verifications can comprise checks on the initial design studies as well as field inspections of the equipment, or even ten-yearly tests such as the containment tests. Any deviations detected during these investigations are then restored to conformity within a time-frame commensurate with their potential consequences. Ageing control is also incorporated into this part of the review. ∙ ∙ The safety reassessment: this step aims to improve the level of safety in the light of the experience acquired during operation, changing knowledge, the requirements applicable to the more recent facilities and international best practices. Following these reassessments, EDF identifies the modifications it intends to make to its facilities in order to reinforce their safety. • The review process for the EDF nuclear power reactors In order to benefit from the standardisation of the NPP reactors operated by EDF, these two parts of the review are first the subject of a generic design programme for a given plant series (900 MWe, 1,300 MWe or 1,450 MWe reactors). The results of this programme are then implemented on each of the nuclear power reactors on the occasion of its periodic safety review. EDF more particularly carries out a large part of the checks and modifications related to the periodic safety reviews during the ten-yearly outage inspections of its reactors. In accordance with the provisions of Article L. 593-19 of the Environment Code, following this review, the licensee sends ASN a periodic safety review conclusions 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 in the Decree of 2 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 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 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 controlling 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 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, 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 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. ASN report on the state of nuclear safety and radiation protection in France in 2018  307 10 – EDF NUCLEAR POWER PLANTS 10