Investigation of the interaction between heat transport systems during the natural circulation decay heat removal in FBR; Investigation of analysis methods using one-dimensional network analysis code

Kimura, Nobuyuki; Nishimura, Motohiko; Momoi, K.; Hayashi, Kenji; Kamide, Hideki 

To enhance reliability and safety of FBR, taking advantage of its inherent properties is of importance. From this point of view, natural circulation decay heat removal (NC/DHR) has been studied in which no active components such as pumps are used. DRACS (Direct Reactor Auxiliary Cooling System) is an option of NC/DHR systems. which causes cold coolant flow from DHX (Direct Heat Exchanger) penetrating into inter wrapper gaps: IWF (Inter-Wrapper Flow). Another option for NC/DHR is to use PRACS (Primary Reactor Auxiliary Cooling System) in which no remarkable IWF occurs. Thermal-hydraulic behavior in the core depends on interactions among auxiliary reactor cooling system, IHX (Intermediate Heat Exchanger), and the secondary loop during NC/DHR. Such interactions have been studied with the test rig called PLANDTL-DHX equipped with DRACS and PRACS. In this study, influence of operating condition of the auxiliary cooling systems and the secondary loop of IHX were examined on the core thermal-hydraulic bchaviors. In the present paper, one-dimensional network analyses using LEDHER code are reported. The analyses were performed on steady tests using two models: a model taking account of an inter-subassembly heat transfer only, and a model simulated both IWF and the inter-subassembly heat transfer. The calculation method was validated through comparisons with the experimental results. In the cases cooled by PRACS or IHX, two calculated models showcd good agreements with the experiments regarding the natural circulation flow rate, the temperature distribution in the core and the temperature at the inlet/outlet of the heat exchangers. However, in the case cooled by DRACS operated, the model without flow pass of IWF could not simulate the experiments with respect to the natural circulation flow rate (12% larger than experiment) and temperature profiles in the inter wrapper gaps. On the other hand, the model taking account of IWF simulated the experiments in good ...