Consideration of natural hazards of extreme intensity Following the accident that struck the Fukushima Daiichi NPP on 11 March 2011, stress tests led ASN to prescribe the installation of a hardened safety core of material and organisational provisions to deal with situations arising from external natural hazards of extreme intensity, the severity of which exceeds that considered hitherto in the baseline safety requirements of each installation. The external natural hazards considered for the design of the hardened safety core are the following: earthquake, flooding (including extreme rainfall) and associated phenomena (extreme winds, lightning, hail) as well as tornados. 2.4.6 Assessment of the risk prevention measures relating to hazards ASN checks that risks linked to hazards in the NPPs are taken into account, notably based on the reassessment of the design of the installations during the periodic safety reviews, analysis of the licensee’s baseline safety requirements, examination of significant events and the inspections performed on the sites. The Fukushima Daiichi NPP accident led EDF to reinforce its organisation for the management of risks relating to hazards. More specifically, networks of coordinators were set up for all the NPPs to oversee the implementation of the actions defined to deal with these hazards. Annual reviews are also held to improve this organisation. In general, ASN considers that major efforts are still needed on most of the sites to improve how hazard risks are dealt with, in particular with regard to: ∙ the maintenance of equipment (sluice gates, fire doors, sensors, floor drains, etc.); ∙ risk assessments during maintenance operations and in the event an equipment malfunction is detected; ∙ compliance with the corrective action deadlines identified by the annual reviews; ∙ training of the coordinators and awareness-raising among the EDF and contractor personnel. Fire risks ASN finds no significant change with regard to control of fire risks within the NPPs. Even if progress is noted on some sites, most of them remain stable, with an overall level of performance below what is expected. The number of fire outbreaks in 2023 is similar to that in 2022. Four outbreaks of fire that occurred in 2023, including one in a controlled area, led to activation of the PUI on the site concerned. ASN has observed certain improvements in the management of the fire risk in the NPPs, notably in management of detection and in personnel training. However, ASN also noted the need to improve certain areas, such as monitoring sectorisation equipment and handling of anomalies concerning it, or the temporary storage of combustible materials during worksites and maintenance operations. EDF also continued with its measures to improve management of the fire risks in the premises identified as being particularly sensitive to this hazard in the light of the potential consequences for safety. Finally, ASN notes that EDF is working on deploying a new firefighting organisation on its site, so that it can more effectively tackle fires and prevent them from spreading. Changes are thus planned with regard to personnel individual protection equipment, training and organisation with the Departmental Fire and Emergency Services (SDIS), which as of 2024 will be deployed on the NPPs. On several sites, this will result in an improved intervention capacity in conjunction with the SDIS. Explosion risks ASN checks the prevention and monitoring measures taken by EDF with regard to the risk of explosion. As part of its labour inspectorate duties, ASN also ensures compliance with the “EXplosive ATmospheres” (ATEX) regulations to ensure worker protection. ASN considers that the level of explosion-related risk management is not yet up to the required standard for all sites. EDF’s maintenance and inspection doctrine is not always applied satisfactorily, notably with regard to the risks related to the presence of hydrogen in the installations. ASN however notes the efforts made by EDF to reduce the deviations found, notably through the implementation of reinforced monitoring and deployment of specific action plans. ASN considers that EDF must continue to pay particular attention to this subject and ensure that it is dealt with using all necessary rigour on all the sites. Internal flooding risks In 2019, ASN asked EDF to supplement its approach in order to better control the internal flooding risk, notably to ensure correct operation of the floor drains, reinforce its maintenance of the lines liable to lead to internal flooding and ensure improved management of their ageing. In response to these requests, EDF implemented improvement measures. In addition, EDF is continuing its field visits to identify the piping which could cause internal flooding in the electrical buildings, which are particularly vulnerable to this risk, in order to assess the need to reinforce its maintenance. In accordance with ASN’s requests, EDF will extend these surveys to the other buildings. ASN sees as positive the fact that EDF has initiated the refurbishment of the circuits of certain cooling systems that are particularly susceptible to corrosion. Finally, for the fourth periodic safety review of the 900 MWe and 1,300 MWe reactors, EDF has updated its safety case regarding internal flooding risks, notably by considering several possible water flow routes, and has defined additional provisions to mitigate the risks. Seismic risks The inspection programmes implemented by EDF lead it to regularly report significant safety events owing to the lack of seismic resistance of certain equipment. These events are the result of targeted inspections gradually being deployed by EDF. These non-compliances can have serious consequences in the event of an earthquake and they are thus systematically analysed. On 11 November 2019, an earthquake occurred in the municipality of Le Teil. EDF implemented the operating procedure required in the event of an earthquake on the Cruas-Meysse NPP. This was because the seismic motion detected on this site reached the level requiring shutdown of the reactors so that checks could be carried out. An inspection programme was then defined and carried out before the reactors were restarted. In November 2019, ASN asked EDF to determine whether this earthquake should lead to a revision of the seismic levels to be adopted for protection of the Tricastin and Cruas-Meysse NPP sites. After field investigations, EDF defined a new design response spectrum for the CruasMeysse site. This spectrum will be used to initiate the seismic re-evaluation studies associated with the fourth periodic safety review of this site. ASN also asked EDF to continue with its investigations in order to obtain an improved characterisation of the existing faults round the Tricastin and Cruas-Meysse NPPs. 304 ASN Report on the state of nuclear safety and radiation protection in France in 2023 • 10 • The EDF Nuclear Power Plants
RkJQdWJsaXNoZXIy NjQ0NzU=