Global sensitivity analysis for core hot spot evaluation under natural circulation decay heat removal in sodium-cooled fast reactor

Doda, Norihiro  ; Kamide, Hideki ; Ohshima, Hiroyuki; Watanabe, Osamu*

In the design study for Japan Sodium Cooled Fast Reactor (JSFR), fully natural circulation system is adopted as the decay heat removal system. We have been developing a new evaluation method of core hot spot in transition from rated operation to natural circulation decay heat removal conditions. Since the method is currently based on conservative assumptions and data, there is room for further rationalization of the safety margin which can be achieved by conducting best estimate analyses with confidence and with quantified uncertainty of results. This paper describes a development of PIRT (Phenomena Identification and Ranking Table) and the global sensitivity analyses of the uncertainties in the event of loss of external power as the first step to improve the evaluation method.