Safety Method for the Preconceptual Phase of Sodium-Cooled Fast Reactors

The European sodium fast reactor-safety measures assessment and research tools (ESFR-SMART) project (Contract number: 754501) focuses on the development of innovative safety design options for future sodium-cooled fast reactors (SFRs). The goal of this paper is to show how the objective provision tree (OPT) method, which is part of the integrated safety analysis methodology (ISAM) developed by generation IV International forum (GIF), can help in defining safety guidelines for the definition and the study of ESFR-SMART innovative design options. The objective provision tree method provides a view of the implementation of main safety functions in accordance with defense-in-depth principle. The method has been adapted to ESFR-SMART needs and guidance for a consistent and homogeneous application has been developed. The method is developed for each safety function with a specific adaptation for the confinement function. Beyond the allocation of the main equipment ensuring the safety functions to the different levels of defense-in-depth, the adapted method proposes a systematic identification of the mechanisms likely to degrade them. Then, safety features to cope with these mechanisms are investigated as well as the potential common cause failures of main equipment belonging to different levels of defense-in-depth. This adapted method allows to study and then to improve the independence between the levels of defense-in-depth as required for future reactors in Europe by Western European Nuclear Regulators' Association (WENRA). The paper provides the outline of guidance for OPT method adaptation to ESFR-SMART project needs, examples of application, and main outcomes of the use of the method.