LES ACTIVITÉS NUCLÉAIRES : RAYONNEMENTS IONISANTS ET RISQUES POUR LA SANTÉ ET L’ENVIRONNEMENT 2.4.5 – Protection against internal and external hazards The NPPs must be able to withstand a variety of hazards, originating either inside or outside the installations. The main hazards constituting a risk for safety are detailed below. Fire risks A fire can lead to failure of the equipment needed to control the fundamental safety functions. Steps must thus be taken to protect the sensitive parts of the facility against fire. In the same way as the other BNIs, NPPs are covered by ASN resolution 2014-DC-0417 of 28 January 2014, relating to the rules applicable to BNIs for controlling fire risks. The way the fire risk is taken into account in the NPPs is based on the “Defence in Depth” principle built around three levels, that is the design of the facilities, fire prevention, fire detection and firefighting. Design rules aim to prevent a fire from spreading and mitigate its consequences; they are based primarily on “fire sectorisation”. This involves dividing the facility into sectors and containment areas designed to keep the fire within a given perimeter bounded by physical items (doors, walls and fire dampers) offering a specified fire resistance duration. The main purpose is to prevent a fire from spreading to two redundant equipment items performing a fundamental safety function. Explosion risks An explosion can damage the items essential for maintaining safety or lead to rupture of the containment and the dispersal of radioactive materials into the facility, or even into the environment. Steps must thus be taken by the licensee to protect the sensitive parts of the installation. Internal flooding risks An internal flood, that is originating inside the facility, can lead to failure of the equipment needed to control the fundamental safety functions. Flooding may in particular be caused by an earthquake. Steps are therefore taken to prevent internal flooding (maintenance of piping carrying water, etc.), or mitigate its consequences (presence of floor drains and water extraction pumps, installation of sills or leaktight doors to prevent the flood from spreading, etc.). Seismic risks Although seismic activity in France is moderate, EDF’s inclusion of this risk in the safety case for its nuclear power reactors is the subject of constant attention on the part of ASNR, given the potential consequences for the safety of the facilities. Seismic protection measures are designed into the facilities. They are periodically re-examined in the light of changing knowledge, on the occasion of the periodic safety reviews. Basic Safety Rule (RFS) 2001-01 of 31 May 2001 defines the methodology used to determine the seismic risk for surface BNIs. This RFS is supplemented by ASN Guide No. 2/01 of May 2006 which defines acceptable calculation methods for a study of the seismic behaviour of nuclear buildings and particular structures such as embankments, tunnels and underground pipes, supports or tanks. The design of the buildings and the equipment important for safety in the NPPs must thus enable them to withstand earthquakes of an intensity greater than the strongest earthquakes that have occurred in the region. EDF’s NPPs must thus be able to withstand seismic levels incorporating the local geological features specific to each one. As part of the periodic safety reviews, the seismic reassessment consists in verifying the adequacy of the seismic design of the facility, taking account of changing knowledge about seismic activity in the region of the site or the methods for assessing the seismic behaviour of structures and equipment. The lessons learned from international experience feedback are also analysed and integrated into this framework. The seismic reassessments regularly lead EDF to reinforce the strength of its installations. Heatwave and drought risks During the heat waves in 2003 and 2006, some of the watercourses used to cool NPPs experienced a reduction in their flow rate and significant warming. Significant temperature rises were also observed in certain NPP premises housing heat-sensitive equipment. EDF took account of this OEF and reassessed the operation of its facilities in air and water temperature conditions more extreme than those initially included in the design. In parallel with development of these “extreme heat” baseline safety requirements, EDF modified its installations (such as the increase in the capacity of certain heat exchangers) and implemented operating practices optimising the cooling capacity of the equipment and improving the resistance of equipment susceptible to high temperatures. During the reactors’ periodic safety reviews, EDF takes account of climate change and is continuing to improve the capacity of its installations to deal with the effects of a heat wave. The capacity of certain cooling systems for equipment required for the nuclear safety case will in particular be improved. EDF has also initiated a climatic monitoring programme to anticipate climate changes which could compromise the temperature hypotheses adopted in its baseline requirements. As with the other hazards, ASNR asks EDF to learn the lessons from the various heatwave events, along with their effects on the installations. 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 selected for the design of the “hardened safety core” are: 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 ASNR 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 in 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, ASNR notes the efforts made by EDF on its sites to improve control of the risks associated with hazards, in particular with regard to the training of the coordinators and awareness-raising among the EDF and contractor personnel. Fire risks In 2025, ASNR noted a slight improvement in the control of firerelated risks within NPPs, particularly at plants that had been judged to be in difficulty in this area in previous years. However, the overall performance level is below that expected. In 2025, four fire outbreaks outside the nuclear zone led to activation of the PUI on the sites concerned, but had no impact on safety. ASNR Report on the state of nuclear safety and radiation protection in France in 2025 295 01 05 02 06 03 07 04 08 09 10 11 13 12 A / Z
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