ASN Report 2020

Regulatory reference files The licensee is required to keep and update the regulatory reference files required by the above-mentioned Order of 10 November 1999 with regard to MPS and MSS monitoring. These files consist of design, manufacture, overpressure protection files, materials files, in-service observations and, as applicable, deviations processing files. The licensee is required to update these files as often as necessary and at periodic requalification of the main primary and secondary systems. Owing to the standardised nature of the French NPP reactors, EDF can perform a generic update of these files. For the fourth periodic safety reviews of the 900 MWe reactors, EDF carried out this update, which is particular in that the design hypotheses were initially produced for 40 years of operation. ASN thus examined the hypotheses and methods used by EDF for updating the equipment files. The entire analysis was the subject of an opinion from the GPESPN on 8 October 2019. ASN also examined all the monitoring programmes scheduled for the MPS and MSS equipment. Following this examination, ASN considered that the overall approach adopted by EDF is satisfactory, while nonetheless asking it to reinforce certain examinations. Operation of Pressure Equipment ASN considers that the situation of the second containment barrier is a point requiring continued vigilance in 2020, the year having been marked by the detection of significant levels of fouling in the SGs on some reactors, liable to impair their operating safety. This finding revealed the inability of maintenance to guarantee a satisfactory level of cleanness. The monitoring strategy for the secondary part of the SGs deployed by EDF was revised in mid-2020 to better prevent these situations. In addition to its assessment of this situation, ASN notes that replacement of the SGs for Gravelines NPP reactor 6 had to be postponed again because of deviations affecting the manufacture of this equipment. The in-service monitoring of the other MPS equipment, pursuant to the Order of 10 November 1999, is carried out appropriately. In 2017, the detection of a crack in a reactor vessel bottom head penetration on the Cattenom NPP reactor 3, the cracking of two plugs installed on the SG of the Paluel NPP reactor 1 in 2016, the perforation of five SG tubes on reactors 2 of the Belleville-sur- Loire and Flamanville NPPs in 2019, the perforation of an SG tube on the Belleville NPP reactor 1 and detection of a boiler effect in an SG of the Nogent-sur-Seine NPP reactor 1 in 2020, illustrate the risk of further deterioration associated with the ageing of the installations. In response to the situations encountered in 2020, EDF reinforced its maintenance and inspection provisions, by increasing the level of stringency and developing new repair processes. 2.3  The containments 2.3.1 Monitoring the containments The containments are monitored and tested to check their compliance with the safety requirements. More specifically, their mechanical behaviour must guarantee good tightness of the reactor building if the pressure inside it were to exceed atmospheric pressure, which can happen in certain types of accidents. This is why, at the end of construction and then during the ten-yearly inspections, these tests include an inner containment pressure rise with leak rate measurement. These tests are required by the Order of 7 February 2012, setting the general rules concerning Basic Nuclear Installations (BNIs). 2.3.2 Assessment of the condition of the containments Overall management of the containment function ASN observes occasional but recurring unavailability of certain equipment participating in the containment function, such as the points of access to the interior of the containment (airlocks and equipment hatch), the circuit depressurising the annulus between the double-wall containments or the control room ventilation system. These unavailabilities will require an analysis and discussions with EDF in 2021 in order to identify any improvements needed. Since 2016, EDF has also been carrying out an action plan with the main aim of guaranteeing that the flowrates in the ventilation systems meet the safety requirements both for the containment and for thermal conditioning of the installations, in the light of the changes made to the reactors since they were built. In order to achieve this goal, the action plan is being deployed, reactor by reactor, on all the ventilation systems concerned, and includes an inventory of the condition of the equipment and ducts. Whenever necessary, EDF is carrying out repairs and improvements and making the necessary adjustments to the ventilation flowrates. In order to check correct implementation of this plan and attainment of the corresponding safety objectives, ASN will be conducting a campaign of dedicated inspections in 2021. Single wall containments with an internal metal sealing liner The ten-yearly tests on the 900 MWe reactor containments carried out since 2009 for their third ten-yearly inspections did not generally bring to light any particular problems liable to compromise their operation. The containment of Bugey NPP reactor 5 did however need to be repaired, following damage to the tightness of its metal liner at the lower part of the reactor building, observed in 2015. EDF implemented specific monitoring. The tightness of this containment will receive particularly close attention during the fourth periodic safety review of this reactor in 2022. The results of the tests on the containments of the 900 MWe reactors, carried out for the first time during their fourth ten- yearly outage on Tricastin NPP reactor 1 and Bugey NPP reactor 2, were satisfactory. Monitoring of the containments was examined by ASN as part of the generic phase of the fourth periodic safety review of the 900 MWe reactors. ASN considers that monitoring must also cover the cleanness of the containment domes and that EDF must provide appropriate means of investigation for the pre-stressing tendon anchor zones on these domes. Double-wall containments The tests on the double-wall containments performed during the first ten-yearly outages of the 1,300MWe reactors detected a rise in the leak rate from the inner wall of some of them, under the combined effect of concrete deformation and a loss of pre- stressing of certain tendons that was greater than anticipated at the design stage. EDF then initiated major work consisting in locally applying a resin sealing coating to the interior and exterior surfaces of the inner wall of the containments of the most severely affected 1,300MWe reactors, as well as to the 1,450MWe reactors. This work continued in 2020. The tests performed since completion of this work have all complied with the leak rate criteria. ASN remains vigilant with regard to changes in the leaktightness of these containments and to maintaining the long-term effectiveness of the coatings. 294 ASN Report on the state of nuclear safety and radiation protection in France in 2020 10 – THE EDF NUCLEAR POWER PLANTS