Development of Core Hot Spot Evaluation Method for Natural Circulation Decay Heat Removal in Sodium Cooled Fast Reactor

Abstract

Toward the commercialization of fast reactors, a design study of Japan Sodium-cooled Fast Reactor (JSFR) is being performed, in which fully natural circulation system is adopted as the decay heat removal system.A new evaluation method of core hot spot which can be applied to natural circulation decay heat removal has been developed.The new method consists of three-step thermal hydraulics analyses in order to consider the effects of physical phenomena particular to natural circulation, such as inter-fuel-assembly heat transfer and flow redistribution in the core due to buoyancy force.From the viewpoint of calculation cost reduction, we have also developed a simplified model substituting for the third step analysis (subchannel analysis).The new method was applied to the evaluations of a loss-of-external- power event and of a sodium leakage accident in a secondary loop of a large scale reactor.