EPR reactor – Flamanville 3 1. Islanding is an operation that takes place when the electricity network fails. It consists of isolating the reactor from the external electricity grid, while maintaining power. The reactor then produces, via its alternator, only the electrical energy it needs to operate in a safe state. The Flamanville EPR reactor was commissioned on 8 May 2024. The first nuclear chain reaction took place on 3 September 2024 and the reactor was coupled to the French electricity grid for the first time on 21 December 2024. Start-up operations have continued into 2025, with two stages subject to authorisation by ASNR: the increase in power to over 25% in April 2025 and the increase in power to over 80% in December 2025. The reactor then reached full power on 14 December 2025. The notable events of 2025 for the Flamanville EPR are detailed in section 4 of chapter 8 of the full ASNR Report. In 2025, ASNR’s oversight is focused on the continuation of start-up tests, the operation of the reactor up to full power and on taking account of operating experience feedback. ASNR considers that the start-up tests were well conducted by the licensee. Although operating activities have been brought under control, an improvement of the robustness of the organisations is expected in certain areas, in particular with a view to the first reactor outage for maintenance and refuelling (see highlight 14 in chapter 8 of the full ASNR Report). With regard to start-up tests, ASNR has carried out an investigation of the results of tests on the reactor core at different power levels, as well as the results of tests on certain major reactor transients, such as reactor shutdown at power, turbine tripping, islanding(1) of the reactor and loss of all external power supplies. For this last test, ASNR carried out a dedicated inspection to verify the appropriate behaviour of the installation during this transient. ASNR considers that these tests were carried out satisfactorily and that the results do not call into question the safety of the installation. To this end, in 2025, it has successively authorised the switch to a power level higher than 25% and 80% of the reactor. With regard to the operation of the reactor, ASNR has continued the inspections initiated in 2024 through a programme of thematic inspections, as it does for the other reactors in the fleet in operation. These inspections covered a wide range of topics, including a designcritical inspection covering both incident and accident management and crisis organisation (see highlight 8 in chapter 8 of the full ASNR Report). These inspections revealed a satisfactory situation in most of the areas inspected. Nevertheless, significant improvements are expected, particularly in the implementation of emergency management premises, the handling of deviations, the management of incidents and the prevention of contamination. In these areas, the inspections revealed organisational shortcomings, both in the formalisation of organisations, in the licensee’s baseline requirements and in the actual implementation of the expected organisation. ASNR considers it essential for EDF to make progress on these issues in the run-up to the first reactor outage for maintenance and refuelling, scheduled for 2026. In addition, ASNR carried out reactive inspections in connection with the licensee’s handling of hazards (unplanned clogging of heat exchangers and leaks found on primary circuit valves), which showed that activities were well under control. ASNR also monitored the way in which Operational Experience Feedback (OEF) from the first few months of reactor operation was taken into account, in particular through inspections in the areas of operation, implementation of parameters in the instrumentation and control system and taking into account OEF from EPR reactors installed abroad. ASNR considers that EDF is making adequate use of OEF from the first months of reactor operation and is maintaining an important link with its counterparts abroad to benefit from international feedback. In 2025, the site reported a decrease in the number of significant safety events compared to 2024, but still a significant number (a large proportion of which were classified as level 1 on the INES scale), compared with the plant in operation. These events are mainly linked to non-compliance with operating specifications by the teams in charge of running the reactor, in particular due to a lack of control over the installation’s configuration. In addition, a number of events were linked to problems with the operational implementation of the periodic test rules used to test equipment, and to incomplete risk analyses when work was carried out on the instrumentation and control system. Finally, it should be noted that few events were caused by material failures, with the exception of the leaks found on the primary circuit valves, which were rectified, and an unplanned clogging of the heat exchangers, for which the storage conditions were not suitable. Normandie THE INSTALLATIONS AND ACTIVITIES TO REGULATE COMPRISE: ▸ basic nuclear installations: • the NPPs of Flamanville (2 reactors of 1,300 MWe), Paluel (4 reactors of 1,300 MWe), Penly (2 reactors of 1,300 MWe) and Flamanville 3 (1 reactor of 1,600 MWe) operated by EDF, • the construction site of two EPR 2-type reactors at Penly, • the Orano spent nuclear fuel reprocessing plant at La Hague, • the Manche repository (CSM) of the French National Radioactive Waste Management Agency (Andra), • the National Large Heavy Ion Accelerator (Ganil) in Caen; ▸ small-scale nuclear activities in the medical sector: • 8 external beam radiotherapy departments (28 devices), • 1 proton therapy department, • 1 brachytherapy department, • 13 nuclear medicine departments, • 50 centres practising fluoroscopy-guided interventional procedures, • 70 computed tomography scanners, • some 2,100 medical and dental radiology devices; ▸ small-scale nuclear activities in the industrial, veterinary and research sectors: • about 450 industrial and research centres, including 27 companies with an industrial radiography activity, • 5 particle accelerators, including 2 cyclotrons, plus a third cyclotron for hadron therapy currently being installed, • 21 laboratories situated mainly in the universities of the region, • 5 companies using gamma ray densitometers, • about 260 veterinary surgeries or clinics practising diagnostic radiology, 1 equine research centre and 1 equine hospital centre; ▸ activities associated with the transport of radioactive substances; ▸ ASNR-approved laboratories and organisations: • 9 head offices of laboratories approved for taking environmental radioactivity measurements, • 2 organisations approved for radiation protection checks, • 4 organisations approved to measure radon in public buildings. Chap.7 Chap 6 Chap.5 ABSTRACTS – ASNR Report on the state of nuclear safety and radiation protection in France in 2025 73
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