ASN Report 2017

353 ASN report on the state of nuclear safety and radiation protection in France in 2017 Chapter 12  - EDF Nuclear Power Plants reviews to be based on a known and robust actual status of the facilities. In 2016 and in 2017, ASN identified the management of deviations affecting NPPs as one of its priority inspection topics. The results of the inspections carried out in 2017 again highlight the difficulties encountered by the NPPs with identification, characterisation and handling of deviations. The inspections carried out or requested by ASN in 2017 during the scheduled reactor outages and during reactor production periods, revealed a number of deviations which called into question the actual availability of certain systems important for the safety of the installations, such as the electrical systems or the heatsink. Some of the defects identified are linked to equipment design. This is for example the case of the significant event, rated level 2 on the INES scale, concerning the inability to demonstrate the capacity of the civil engineering anchors of the auxiliary systems of the diesel generator sets on the Fessenheim and Bugey 1,300 MWe reactors to withstand an earthquake. Other defects are linked to the poor condition or to non-compliance with the equipment drawings: for example, insufficient seismic resistance owing to corrosion which developed because of a lack of appropriate preventive maintenance of certain pipes, which could lead to the total loss of the heatsink for certain 900 MWe reactors, or non-conformity in the supports of piping on the essential service water system of some reactors in the Gravelines NPP. ASN considers that these numerous deviations, some of which were rated level 2 on the INES scale in 2017, are indicative of a deterioration in the real condition of the facilities and that EDF must significantly improve its management of the conformity of its facilities. ASN required the repair of the most significant deviations without delay and carried out inspections to check the satisfactory completion of these repairs. ASN will be particularly attentive as to how the situation develops in 2018 and will in this respect continue its inspections of the condition of equipment and systems. Control of the conformity of the facilities in operation will be a major focal point for ASN oversight in 2018 and it will notably be examined with a view to preparing for the fourth periodic safety review of the 900 MWe reactors, for which the first of wich is scheduled as of 2019. Analysis of significant events statistics In accordance with the rules concerning the notification of significant events (see point 3.3 of chapter 4), EDF in 2017 notified ASN of 688 significant safety events, 130 radiation protection events and 98 environmental protection events. Graph 1 shows how the number of significant events notified by EDF and classified on the INES scale has evolved since 2008. Graph 2 shows the trend since 2008 in the number of significant events according to the notification field: Significant Safety Events (ESS), Significant Radiation Protection Events (ESR) and Significant Environmental Events (ESE). Several events which are similar or the result of common causes affect several NPPs. They are grouped under the term Generic Significant Events (ESG). Seventeen were notified in 2017 in the field of safety, one in the field of radiation protection and one in the environmental field. The number of significant events increased by about 17% in 2017 by comparison with the previous year. The details of the significant events for each site are presented in chapter 8. FOCUS Significant safety even rated level 2 on the INES scale concerning a risk of total or partial loss of the heatsink for 29 reactors On 16th October 2017, ASN rated as level 2 on the INES scale a significant safety event concerning a risk of total or partial loss of the heatsink for 29 reactors. Following an ASN request, EDF carried out checks on the piping of the fire-fighting water production system (also called the JPP system) in the Belleville-sur-Loire NPP in the spring of 2017. On two sections of the JPP system, these checks revealed that the piping was degraded, with a thickness unable to meet the minimum requirements such as to guarantee earthquake resistance. This degradation is the result of corrosion which developed given the lack of appropriate preventive maintenance. The EDF analyses led it to extend its investigations to the piping of the raw water filtration system (called the SFI system or CFI system depending on the configuration of the nuclear site) and to all the reactors in service. The piping concerned (JPP and SFI or CFI) is located in the pumping station of the essential service water system (SEC system), which functions permanently and which, using the heatsink available near the installation (sea or watercourse), contributes to cooling of the safety systems. In the event of an earthquake, rupture of the JPP, SFI or CFI piping could lead to flooding of the SEC system pumps and thus loss of this cooling capacity essential to the NPP. EDF implemented solutions to repair the defective piping sections and compensatory measures to rapidly secure the two redundant channels of the SEC system and aims to complete the final repairs by the end of 2018. ASN checked that EDF was taking all necessary steps to deal with this event as rapidly as possible. It will ensure that EDF learns all relevant lessons from this event, notably with regard to improving preventive maintenance provisions.