In order to achieve increase of power outputs of an ABWR, it is extremely important to evaluate coolant flow in a lower plenum. Numerical simulation is helpful to predict the coolant flow, and thus verification experiments are needed. Hence, the present study is focusing on the construction of benchmark of CFD code. The objective of the study is to clarify relation between flow distribution to the core and the complicated flow structures in the lower plenum.

We constructed a 1/10 model of a lower plenum to conduct flow experiment for validation of CFD analysis. In the experiment, it turned out that coolant flow distribution becomes to be uniform at core support beam, and there are complicated flows like vortices around side entry orifices. Regarding differential pressure distribution, it was revealed that profile of the region including side entry orifices is very dominant. This pressure loss might be caused by contraction flow at the orifices. Such flow structures were also described by CFD analysis. As good performance of analysis, we investigated flow distribution to the core particularly by using CFD results. And relation between the flow distribution and the complicated flow structures were also discussed.

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