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

THE ASN RESOLUTION ASN underlines the very substantial work carried out by EDF on the mitigation of the consequences of accidents with core meltdown and the ambitious nature of the associated modifications programme. This programme will bring major progress in safety and meet the targeted objectives of this safety review. Nevertheless, in the light of its examination, ASN considers that EDF must supplement the planned measures for managing an accident with core meltdown, more specifically by: • reinforcing certain concrete walls in the premises in which the corium would spread; • means for injecting an additional volume of borated water in the reactor building. These points are set out as requirements in ASN resolution 2021-DC-0706 of 23 February 2021. EDF has adopted the objective of preventing lasting environmental effects in the event of a core meltdown accident. EDF has thus planned to modify its facilities in order to: • be able to remove the heat produced by the core to the exterior of the containment , without it being necessary to depressurise the containment. This greatly reduces the releases of radioactivity into the atmosphere; • be able to cool the corium that has melted through the reactor vessel in the bottom of the reactor building and avoid melt-through of the lower concrete slab. This limits the pollution of the groundwater. What measures are planned by EDF? EDF plans setting up systems for managing such accidents more effectively. This will involve putting in place, during the 10-yearly outage, new systems (including new pumps, new pipes, new heat exchangers) forming part of the “hardened safety core”, modifications in the reactor pit and in certain neighbouring premises, along with the mobile means deployed by EDF’s Nuclear Rapid Intervention Force (FARN). Lastly, EDF plans taking measures to limit leaks of contaminated water outside the reactor building and the fuel building in the event of an accident leading to core meltdown, and to have means for reducing contamination of the water present in the reactor building following an accident that has resulted in core meltdown. In order to limit the extent and duration of contamination should contaminated water leak outside the building, EDF shall also examine – for each site – the means of limiting the dispersal of radioactive substances outside the site, through the soil and the groundwater. Conditions for the continued operation of EDF’s 900MWe reactors • 17