Application of integrated safety assessment methodology (ISAM) to Japanese sodium-cooled fast reactor (JSFR)

Kurisaka, Kenichi ; Shimakawa, Yoshio*

JAEA participates in activities of the Generation IV International Forum's Risk and Safety Working Group (GIF/RSWG). The GIF/RSWG has developed the Integrated Safety Assessment Methodology (ISAM), which consists of five distinct analytical tools; i.e., Qualitative Safety Features Review, Phenomena Identification and Ranking Table (PIRT), Objective Provision Tree (OPT), Deterministic and Phenomenological Analyses (DPA) and Probabilistic Safety Analysis (PSA). Among them, PIRT, OPT, DPA and PSA were applied preliminarily to the Japanese Sodium-cooled Fast Reactor (JSFR) system. The JSFR system includes major innovative safety features such as Self-Actuated Shutdown System (SASS), passive decay heat removal system. PIRT was applied to examination of the reactor safe shutdown by means of SASS during a loss-of-flow accident with a failure of conventional reactor shutdown system. OPTs were developed to assess the structure of safety architecture of the JSFR in an adequate manner based on the defence-in-depth philosophy. Some provisions explicitly shown in the OPT are characterized with the safety design requirements of decay heat removal function. Sufficiency to those requirements was confirmed by DPA. PSA was conducted with analytical models, which were based on those OPT and DPA results. The PSA served to quantification of the level of safety and to the system design improvement in the JSFR.