E204 Development of Core Hot Spot Evaluation Method for Decay Heat Removal by Natural Circulation under Transient Conditions in Sodium-cooled Fast Reactor

Toward the commercialization of fast reactors, a design study of Japan Sodium Cooled Fast Reactor (JSFR) is being performed. In this design study, adoption of fully natural circulation system is being examined as the decay heat removal system from the viewpoints of economic competitiveness and passive safety. This paper describes a new evaluation method of core hot spot for decay heat removal by natural circulation under transient conditions that is necessary for confirming feasibility of the fully natural circulation system. The new method consists of three step analyses in order to include the effects of thermal hydraulic phenomena particular to natural circulation decay heat removal, inter-assembly heat transfer and flow redistribution in fuel assemblies and in the core by buoyancy force, and therefore enables more rational hot spot evaluation rather than conventional ones. The method was applied to an analysis of loss-of-extemal-power event and the result was compared with those by a conventional method and a detailed 3D simulation. It was confirmed that the proposed method can estimate the hot spot with a reasonable degree of conservativeness.