LES ACTIVITÉS NUCLÉAIRES : RAYONNEMENTS IONISANTS ET RISQUES POUR LA SANTÉ ET L’ENVIRONNEMENT specific in-service monitoring programme, defined and periodically revised by EDF and examined by ASNR. Following the inspections, those tubes which are too badly damaged are plugged, to remove them from service. Over time, the SGs tend to become clogged with corrosion products from the secondary system exchangers. The layer of deposits of corrosion products (fouling) that forms on the tubes reduces the heat exchange capacity. On the tube support plates, the deposits (clogging) prevent the free circulation of the water-steam mixture, which creates a risk of damage to the tubes and the internal structures and which can degrade the overall operation of the SG. Several solutions can be implemented to limit metallic deposits in the secondary circuit: cleaning with hydraulic jets, preventive chemical cleaning, replacement of certain materials used to manufacture the condenser tube bundles (brass replaced by more corrosionresistant stainless steel or titanium alloy), modification of chemical products used for conditioning systems and pH increase. Some of these operations must be authorised by ASNR beforehand, because they imply discharges of some of the dangerous substances. Since the 1990s, EDF has been running a programme to replace the SGs with the most severely degraded tube bundles. The SG replacement campaign concerning 26 reactors with a non- heat-treated Inconel 600 tube bundle has now been completed. It is continuing with replacement of SGs on the reactors in which the tube bundle is made of heat-treated Inconel 600 (21 reactors are still concerned). 2.2.4 – Assessment of operation of Nuclear Pressure Equipment Monitoring the operation of reactor main primary and secondary systems ASNR considers that EDF’s surveillance of the operation of the MPS and MSS remains a point warranting particular attention. In 2025, EDF more particularly continued its inspections defined after detection of a stress corrosion phenomenon on the auxiliary piping of the primary systems (see Highlight No. 1). In addition, in 2025, a vibration fatigue leak was detected on a smalldiameter pipe connected to the primary system of reactor 1 at the Flamanville NPP. This pipework, which is not monitored in service, has been inspected and repaired. Vibration fatigue is a known phenomenon and is monitored specifically by EDF for certain types of piping, which was not the case for the pipe in question. ASNR is monitoring the investigations carried out by EDF to determine the causes and any changes to its monitoring programme in this area. Additional controls will be implemented by EDF from 2026. In general, through the programmes of additional investigations on these systems, on the occasion of each periodic safety review, EDF must schedule appropriate checks to take account of the risk of any degradation phenomena not initially expected, in addition to the routine monitoring programmes. The detection since 2021 of stress corrosion cracks in areas where they were not previously a concern confirms the value of such investigation programmes, the content of which is regularly analysed by ASNR. In 2025, EDF also discovered indications during radiographic inspections of welds in the SG water supply system for reactor 1 of the Nogent-sur-Seine NPP. These indications required further investigation to determine their nature and conclude that they were not harmful. The analysis showed that these indications were visible on the films of several successive previous inspections without the necessary actions having been triggered. In this context, EDF sent ASNR a significant event report in July 2025, which was revised in December 2025. ASNR has analysed the action plan that EDF drew up following the discovery of these indications. In particular, it provides for raising the awareness of operators responsible for carrying out inspections in these areas and reinforcing EDF’s oversight of the performance of non-destructive examinations. The implementation of the in-service surveillance programmes on the MPS and MSS, along with their adaptation to take account of changing OEF and knowledge of degradation modes, are thus the subject of particular attention by ASNR. In this respect, ASNR is attentive to ensuring that EDF uses appropriate non-destructive inspection means for which performance has been qualified. EDF must also reactively deploy checks to ensure that there are no particular risks, for example if a new degradation mode is discovered or suspected. The reactor pressure vessels During the periodic safety reviews, ASNR examines the demonstration of the in-service strength of the reactor pressure vessels every ten years. The generic approach implemented by EDF is to use a worst-case approach to verify that all the vessels of a type of reactor offer sufficient resistance to fast fracture, taking account of the loads to which they are subjected in operation (whether during routine, incident or accident operating situations) and their embrittlement under irradiation. During this examination, account is taken of the mechanical properties of each vessel and the presence of a hypothetical flaw positioned in the worst possible place. EDF also specifically checks the mechanical strength of vessels with particular defects. Following its review, ASNR reached a favourable conclusion in 2025 regarding the ability of the 1,300 MWe reactor vessels to continue to function until their fifth ten-yearly outage. However, further information is awaited on the Irradiation Monitoring Programme (PSI) for the reactor vessel of reactor 1 at Penly NPP, which shows that the vessel steel is more brittle than estimated by the generic irradiation embrittlement formula. These additions will be specifically examined by ASNR ahead of the fourth ten-yearly inspection of this reactor, scheduled for 2031. During the ten-yearly outage inspection of each reactor, EDF also carries out checks to ensure that the existing flaws have not developed further, or that prejudicial flaws have not appeared in the steel of the vessels. It also carries out a hydraulic pressure test of the primary system. ASNR issues reports following the checks carried out during each ten-yearly outage inspection of the primary system, and in particular with regard to the pressure vessels. In 2025, the results of the checks carried out were satisfactory. Cast products The methodological principles followed by EDF in its mechanical analyses to justify maintaining these moulded components in service were thus validated by ASNR. This examination concluded that all the elbow assemblies in the primary systems of the 900 MWe reactors can be kept in service at least until the fifth ten-yearly outage. ASNR is conducting an investigation into certain E-bends (bends located close to the reactor vessel) in the reactors at the Paluel NPP, the continued operation of which beyond the forthcoming ten-yearly outage programmes will require special justification. To justify maintaining cast elbow assemblies in service beyond the fifth ten-yearly outage, EDF is continuing its studies in several areas. In particular, EDF plans to ask ASNR to allow it to use more advanced calculation methods to take better account of the nature of the faults likely to be present. EDF is also developing a new means of nondestructive examination of the inner wall of the E elbow assemblies, as well as a technique for repair of defects on the inner wall, which EDF could use if it is not able to provide justification for maintaining them in service. ASNR considers this work to be necessary, as it should allow EDF to define a treatment strategy sufficiently well in advance of the ten-yearly outages. 288 ASNR Report on the state of nuclear safety and radiation protection in France in 2025
RkJQdWJsaXNoZXIy NjQ0NzU=