Investigations of single-phase flow mixing characteristics in a wire-wrapped 37-pin bundle for a sodium-cooled fast reactor

Flow mixing characteristics inside a wire-wrapped 37-pin bundle were measured using a wire-mesh sensing system. The subchannel flow mixing within a sodium-cooled fast reactor (SFR) core subassembly is an important phenomenon to predict temperature distributions for the core thermal design and safety analysis. To identify the mixing characteristics experimentally, a dedicated test facility including the wire-mesh sensor system and tracing liquid injection system was developed. The conductivity fields at the end of a 37-pin bundle were visualized in several different flow conditions which are corresponding to 20-115% flow of the prototype reactor nominal flow based on the Reynolds number. A CFD preliminary analysis under pre-determined boundary conditions was also performed to verify the design parameters and range of various operating values of the current mixing test. The experimentally identified mixing characteristics were compared with the CFD results, which show reasonable agreements with each other. The current experimental work includes the uncertainty evaluation by performing the separated test for the elementary parameters.