Study on the Effect of Branching Outlet Pipe using CFD Method

For a downward flow type research reactor immersed in a pool, coolant passes through the upper guide structure, cools down fuel assemblies in the core, and return to primary cooling loop through outlet nozzle of lower plenum. If the pressure drop of reactor core is too small, flow rates of fuel assemblies in the core may be affected by the flow pattern in the outlet plenum, which depends on the location and number of outlet nozzles. A uniform distribution of coolant flow in the reactor core is required to ensure a thermal-hydraulic safety. If outlet nozzle number could affect the flow distribution in the reactor core, it should be evaluated and fed into the design of reactor structure. This is a numerical study to figure out the effect of branching outlet pipe. CFD analyses for two types of outlet plenum are conducted and the predicted results of flow distribution and fluctuation are compared with each other