EDF then carried out gradual power increases. The reactor was coupled to the electricity grid for the first time on 21 December 2024. When the reactor is started for the first time, EDF has to perform a large number of specific tests to check the correct operation of the systems which could not be tested before fuel was loaded. The purpose of these tests is to check that: • The core, its instrumentation and its protection systems behave as expected at the various power levels. • The nuclear steam supply system and turbine controls are correctly adjusted. • The secondary system, the turbine and the generator work correctly. These tests can only be carried out once enough steam is being produced. • Certain situations, such as reactor trip or turbine shutdown for example, are correctly managed. These tests are particularly closely monitored by ASN, which is kept informed in detail about their performance, the results and any incidents encountered. It also carries out inspections, most of which are unannounced. At the end of 2024, the tests already performed on the reactor’s safety-important systems had taken place satisfactorily. The various events which occurred since reactor commissioning Since the reactor was commissioned, EDF has notified a number of significant safety events that was higher than expected, even for the start-up of a new reactor. These events are primarily related to the learning curve followed by the teams when carrying out initial operation of the reactor and the transition between management of a construction site and actual operation of an installation. The causes of the vast majority of the events are organisational and human, with few being linked to equipment failures. Most of the human errors are rapidly detected and lead to the installation being restored to conformity almost immediately. Faced with this finding, and even if these events had no consequences for the installations, people and the environment, EDF implemented a number of measures to reinforce the oversight and control of its activities. These measures notably consist in stabilising the activity schedules and more clearly identifying and managing the risks before starting an operation. EDF also reinforced the support provided by its national teams. ASN considers that these measures are pertinent and appropriate for the difficulties encountered during this particular phase in the life of the installation. The next steps ASN authorisation was required for the first reactor increase to a power of more than 25% its nominal power. Beyond this power level, the systems required for core protection are different and the Authority for Nuclear Safety and Radiation Protection (ASNR) will in particular check that they are able to perform their function. ASNR approval will again be required before the first increase to a power higher than 80% nominal power. Most of the start-up tests will then have been carried out. After the start-up testing phase, EDF will continue with reactor operation up until the first refuelling outage. During this outage, EDF will conduct specific checks, notably a complete requalification of the main primary system. The licensee will also have to incorporate modifications to the installation and in particular replace the reactor vessel closure head. ASNR will examine these modifications and will check the operations carried out during this outage, as it does for any nuclear reactor. It will pay particular attention to capitalising on the Operating Experience Feedback (OEF) acquired during this phase. Finally, six months after the end of this outage, EDF shall send ASNR an end of start-up file presenting the results of other start-up tests, the OEF from the first operating cycle and shall update the reactor’s safety analysis report and general operating rules. ♦ NOTABLE EVENTS 2024 ABSTRACTS – ASN Report on the state of nuclear safety and radiation protection in France in 2024 15
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