Les cahiers de l’ASN #02 - Conditions for the continued operation of EDF’s 900MWe reactors

EDF has reassessed the severity of the hazards to consider in the light of developments in knowledge, and has substantiated that, in the event of a hazard, the reactor can be shut down and maintained lastingly in a safe state. For hazards of climatic origin, EDF has put in place a surveillance system in order to collect data on heat waves and the rise in sea levels and to reassess the severity of the corresponding hazards. This periodic safety review provides the opportunity to deploy the “hardened safety core” of safety measures prescribed by ASN in 2012 in the wake of the Fukushima NPP accident. What measures are planned by EDF? These measures will make it possible to withstand certain hazards (earthquake, flooding, etc.) of extreme intensity, going beyond the levels considered until now. Most of the studies relative to hazards depend on the sites and will be completed during the safety review phase specific to each reactor. This is the case, for example, with the studies to reassess the earthquake resistance of the facilities. The studies carried out so far have identified a number of necessary modifications , such as the removal of certain water entry routes in conditions of high-intensity rainfall, the installation of grids against projectiles caused by high winds, the installation of fail-safe devices for switching between the external electrical power sources in case of fire, and the addition of molecular hydrogen leak detection and neutralisation systems in the battery charging rooms, as hydrogen can cause an explosion. EDF has moreover checked that the particular ambient environment conditions that could be created in a hazard situation are acceptable in the premises in which actions must be carried out. It has undertaken to supplement its demonstration concerning the ability to route resources to these premises and to carry out, in good time, the requisite actions for all accidents, including those leading to core meltdown. THE ASN RESOLUTION ASN underlines the substantial work carried out by EDF to update all the hazard studies, whether the hazards originate inside or outside the facility. The methods adopted by EDF to define the hazard levels are acceptable. The modifications resulting from these studies represent a significant improvement in the control of the risks associated with hazards and will enable the objectives of the safety review to be achieved. This being said, ASN considers that EDF must, in addition to the initially planned measures, integrate the following in the 4 th periodic safety review of the 900MWe reactors: • a study of the ability of the facilities to cope with even higher temperature levels; • the identification of the most sensitive equipment items whose resistance in the event of fire or explosion is essential for reactor safety, and the defining of measures to reduce the risk of their failure. These points are set out as requirements in ASN resolution 2021-DC-0706 of 23 February 2021. Conditions for the continued operation of EDF’s 900MWe reactors • 13