Numerical simulation of three dimensional flow in the lower plenum

The numerical simulation becomes a very useful tool to compute thermohydraulics flows through complex geometry. The numerical simulation of the turbulent flow in LUCIE model has been done using a Computational Fluid Dynamics(CFD) code TRIOU developed by CEA. 3D Navier Stokes equations are solved using VDF('Volumes differences finites' (finite difference volume)) and VEF('Volume elements finites' (finite element volume)) methods. The computations of steady and unsteady conditions can be allowed. The aim of these computations is to reach a better understanding of the thermal hydraulic phenomena in the lower plenum of a nuclear reactor vessel. The CFD prediction of flow behaviors in the lower plenum was verified by experiment. The results show certain difference between CFD and experiment. So the refined meshes and a parallel calculation are needed for such complicated geometry. Additional information on the mechanism causing vortex formation would be improved by performing other experiments. The turbulence modeling to simulate vortices should be further developed. This CFD analysis confirmed that the CFD method is quite useful and effective for the structure design of a reactor vessel. However it is necessary to investigate with more detail in order to have a good agreement not only when comparing the general flow behavior but also comparing numerical data. (authors)