ASN Report 2020

2.4.3 Monitoring maintenance of the facilities Preventive maintenance is an essential line of defence in main­ taining the conformity of a facility with its baseline safety require­ ments. This is an important topic, checked by ASN during its inspections in the NPPs. In order to improve the reliability of the equipment important for safety but also industrial performance, EDF is optimising its maintenance activities, drawing on practices used in conventional industry and by the licensees of NPPs in other countries. Since 2010, EDF has thus initiated the deployment of a new maintenance methodology, called AP-913, developed by the American nuclear licensees. The main interest of this method is to make the equipment more reliable through in-service monitoring, allowing improvements to preventive maintenance. Deployment of this maintenance methodology is based on implementation of the following six processes: ∙ identification of critical equipment and definition of the associated maintenance and monitoring programmes; ∙ definition of equipment monitoring and maintenance requirements; ∙ equipment and systems performance analysis; ∙ definition and oversight of corrective measures; ∙ continuous improvement of baseline requirements and oversight of reliability; ∙ equipment lifecycle management. After an AP-913 deployment review in 2016, EDF developed its practices in order to guarantee the quality of maintenance work, refocus performance monitoring on the most important equipment and systems and optimise the volume of maintenance operations. 2.4.4 Assessment of maintenance The organisation in most NPPs for successfully carrying out large- scale maintenance was satisfactory in 2020, including in a context made complicated by the Covid‑19 pandemic. However, ASN regularly identifies points for improvement concerning reactor maintenance, such as taking account of the various hazards, the preparation of activities or the traceability of the work done. The procurement of non-conforming spare parts once again this year led to faults in the management of the activities. Incorrectly applied national EDF documents or incorrect operational documents are also the cause of inappropriate maintenance operations or maintenance quality defects. Poor performance of the work is sometimes detected belatedly, in other words only during the operations to requalify the equipment after the maintenance work. Finally, ASN observed that the requalification tests are not always able to detect equipment defects following maintenance or modification work. In 2020, ASN confirms the improvement in the technical oversight of contractor operations and monitoring, particularly through the use of computerised tools recently deployed in the NPPs. However, the root cause of several significant events is still maintenance non-quality undetected by monitoring or by first level analyses. In 2019, ASN asked EDF for a review of its maintenance policy and the adaptations made. In 2021, ASN will examine the replies provided by EDF in 2020, in particular with regard to the observations that it regularly issues. In the context of the continued operation of the reactors, the “major overhaul” programme and all the modifications made as a result of the lessons learned from the accident at the Fukushima Daiichi NPP, ASN considers that it is important for EDF to continue with its efforts to remedy the difficulties encountered and improve the quality of its maintenance activities. 2.4.5 Preventing the effects of internal and external hazards Fire risks In the same way as the other BNIs, NPPs are covered by ASN resolution 2014-DC-0417 of 28 January 2014, relating to the rules applicable to BNIs for controlling fire risks. The way the fire risk is taken into account in the NPPs is based on the principle of defence in depth built around three levels, that is the design of the facilities, fire prevention and firefighting. Design rules must prevent a fire from spreading and mitigate its consequences; they are based primarily on “fire sectorisation”. This involves dividing the facility into sectors and containment areas designed to keep the fire within a given perimeter bounded by items (doors, walls and fire dampers) offering a specified fire resistance duration. The main purpose is to prevent a fire spreading to two redundant equipment items performing a fundamental safety function. Prevention primarily consists in: ∙ ensuring that the nature and quantity of combustible material in the premises remains below the hypotheses adopted for fire sectorisation; ∙ identifying and analysing the fire risks in order to take steps such as to avoid them. More specifically, for all the work liable to generate a fire, a “fire permit” must be issued and protective measures taken. Finally, the detection of an outbreak of fire and fire-fighting should enable a fire to be brought under control and then extinguished within a time compatible with the fire resistance duration of the sectorisation elements. ASN checks that the fire risk is taken into account in the NPPs, notably through an analysis of the licensee’s baseline safety standards, monitoring of significant events reported by the licensee and inspections performed on the sites. The important risks associated with fire have been the subject of numerous ASN requests since 2003 and ASN thus reminded EDF in 2016 that, for the purposes of the fourth periodic safety review of the 900 MWe reactors, it expected a well-structured and robust safety case based on a Defence in Depth approach. ASN is examining the justification methods produced by EDF. These were submitted to the GPR for analysis in 2019. This examination showed that the changes proposed by EDF represented considerable improvements to the safety case (for The Independent Safety Organisation At EDF, the Independent Safety Organisation (FIS) verifies the actions and decisions taken by the departments in charge of operating the installations, from the viewpoint of safety. On each Nuclear Power Plant, the FIS comprises safety engineers and auditors, who conduct a daily check on the safety of the reactors. The working of each FIS is checked and evaluated at a national level by the FIS of EDF’s Nuclear Production Division. Finally, the EDF internal inspectorate, in particular the general inspector reporting to the Chairman of the EDF group, assisted by a team of inspectors, represents the highest level of independent verification of nuclear safety within the EDF group. ASN Report on the state of nuclear safety and radiation protection in France in 2020 297 10 – THE EDF NUCLEAR POWER PLANTS 10