LES ACTIVITÉS NUCLÉAIRES : RAYONNEMENTS IONISANTS ET RISQUES POUR LA SANTÉ ET L’ENVIRONNEMENT Certain cast branch connections on the primary legs (RIS system nozzles on the cold leg) are also sensitive to thermal ageing phenomena and their potential for being maintained in service was analysed, the methodology for which was assessed by IRSN for the 900 and 1,300 MWe reactors. The low toughness of certain spigots on reactors 1 and 2 at Paluel NPP and on reactor 1 at SaintAlban NPP, linked to their ageing, has led EDF to schedule their replacement. The Steam Generators For ASNR, the SGs remain a point meriting particular attention in 2025. The significant fouling and clogging levels detected in certain SGs, liable to alter their operating safety, led to the scheduling of preventive cleaning. Maintenance for achieving satisfactory cleanness has been insufficient in the past and ASNR now considers this to be a point warranting particular vigilance. EDF’s maintenance strategy with regard to clogging and fouling of the secondary part of the SGs is currently evolving. ASNR is also paying particularly close attention to monitoring the deterioration of the SG feedwater rings on the 1,300 and 1,450 MWe reactors. Main Primary System auxiliary lines Numerous stress corrosion or thermal fatigue cracks have been discovered since 2021, in particular on the SIS and RRA lines of the 1,450 MWe and 1,300 MWe type P’4 reactors, in the immediate vicinity of certain welds. This led to numerous checks and repairs being carried out. The investigations will continue in 2026, notably on other systems. In addition, ASNR will issue a position statement in 2026 on the strategy that EDF is implementing for the long-term monitoring of RIS and RRA piping, in order to take account of these risks of cracking (see Highlight No. 1). 2.3 The containments 2.3.1 – The containments The containments, which constitute the third containment barrier, undergo inspection and testing 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 increase, which can happen in certain types of accidents. This is why, at the end of construction and then during the ten-yearly outages, these tests include an inner containment pressure rise with leak rate measurement. These tests are required by the creation authorisation decrees of each reactor and by the Order of 7 February 2012, setting the general rules concerning Basic Nuclear Installations (BNIs). Other equipment takes part in the containment function, such as the systems for allowing access to the interior of the containment (airlocks and equipment hatch), the circuit depressurising the annulus between the double-wall containments, and the control room ventilation system. 2.3.2 – Assessment of the containments Overall management of the containment function EDF’s management of the containment function is on the whole satisfactory. Since 2010, EDF has been carrying out an action plan with the 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. The action plan is being deployed, reactor by reactor, on all the ventilation systems concerned, and includes an inventory of the equipment and ventilation ducts. As necessary, EDF carries out repairs and improvements and adjusts the ventilation flow rates. ASNR notes that ventilation rate adjustments are generally carried out according to schedule, and that EDF adequately justifies any deviations, while providing effective support to sites encountering difficulties. Single-wall containments with an internal metal sealing liner The ten-yearly tests on the 900 MWe reactor containments carried out since 2019 as part of their fourth ten-yearly outages did not bring to light any problems liable to compromise their operation. In 2025, EDF carried out containment tests on three reactors, with satisfactory results. Double-wall containments The tests on the double-wall containments performed during the first ten-yearly outages of the 1,300 MWe 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 tension in certain pre-stressing 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 1,300 MWe reactors, as well as to the 1,450 MWe reactors. For all the reactors on which it was carried out, this work enabled the leak rate criteria to be met during the containment pressure tests. HIGHLIGHT No. 1 Auxiliary lines stress corrosion: review of actions taken Following the discovery of stress corrosion cracks at the end of 2021 on auxiliary lines of the primary system of some of its reactors, EDF set up a programme to inspect more than 1,200 welds in the Safety Injection Systems (RIS) and Residual Heat Removal Systems (RRA). In 2025, EDF continued with the deployment of significant inspection and analysis resources to identify the causes of this degradation. The inspections carried out since the end of 2021 have so far revealed the presence of over 80 cracks more than 2 mm deep on these pipes, which confirms the serious nature of this phenomenon which was not hitherto considered liable to affect these lines. In addition, the checks carried out led to the discovery of around ten cracks caused by thermal fatigue, which is a known mode of degradation likely to affect these pipes. However, some of these cracks were discovered in welds that had not been subject to any particular monitoring. The inspection campaign launched at the end of 2021 is almost complete. By the end of 2026, EDF will have inspected around 55% of the welds on the RIS and RRA lines likely to be affected by this phenomenon. Nevertheless, checks must continue on the pipes of other systems important to safety, in order to confirm that they are not susceptible to stress corrosion cracking. The discovery in 2025 of new stress corrosion and fatigue faults in lines that were replaced in 2022 reinforces the need to continue investigations to understand these phenomena. In particular, several reactors will be instrumented to study the thermalhydraulic behaviour of auxiliary circuits, which is a key factor in the occurrence of stress corrosion and fatigue. To limit the risk of stress corrosion reoccurrence, EDF has initiated the deployment of pipe compression operations. Finally, this phenomenon calls for the implementation of a longterm monitoring strategy for all the piping in the RIS and RRA systems, taking into account the OEF collected since 2021. ASNR is currently examining the strategy proposed by EDF, for which it plans to issue a position statement in autumn 2026. ASNR Report on the state of nuclear safety and radiation protection in France in 2025 289 01 05 02 06 03 07 04 08 09 10 11 13 12 A / Z
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