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

ACCIDENTS WITHOUT CORE MELTDOWN A n accident without core meltdown is an accident during which the nuclear fuel suffers little or no damage. It can nevertheless lead to releases of radioactivity into the environment. Controlling such accidents can prevent core meltdown. The reactor safety case addresses both accidents resulting from a single failure (e.g. a primary system break) and accidents resulting from multiple and cumulative failures (e.g. loss of the site’s internal and external electrical power supplies, known as “site blackout” –SBO). EDF has planned updating its safety case in the light of developments in knowledge. It has set itself the objective of moving towards levels of radioactive releases into the environment that do not necessitate population protection measures (sheltering, evacuation, taking iodine tablets). During the generic phase of the safety review, EDF re-examined all the studies associated with the different accident scenarios. What measures are planned by EDF? More specifically, EDF has assessed the effects of physical phenomena not previously considered in the safety case, such as deformation of the nuclear fuel assemblies. EDF has planned to modify its facilities to mitigate the consequences of certain accidents. In particular, modifications are planned to limit the quantity of radioactive water released into the environment in the event of an accident involving steam generator tube rupture. What is an accident without core meltdown? THE ASN RESOLUTION The modifications planned by EDF will improve the management of incident and accident situations without core meltdown and therefore also improve the preventions of accidents with core meltdown. They will lead to a reduction in the radiological consequences of the accidents studied in the safety case. This will significantly reduce the occurrence of situations requiring population protection measures. EDF must further pursue its efforts to mitigate the radiological consequences of steam generator tube rupture accidents, which lead to the most significant radiological consequences. The results of the studies and the modifications planned by EDF, supplemented by the measures requested by ASN, will enable the targeted objectives of this safety review to be met. 18 • Les cahiers de l’ASN • February 2021 ASN RESOLUTION AND REQUIREMENTS