Computational fluid dynamics analysis of AP1000™ reactor vessel upper plenum and top core slab

The PWR reactor vessel upper plenum contains many control rod guide tubes and support columns, arranged in a chess-board pattern above the upper core plate. Below the upper core plate is the top core region consisting of 157 fuel assemblies, which have components such as the top nozzles that need to be included in this CFD model. Significant computer resources are required to perform detailed fluid flow simulation of the whole upper plenum and top core regions. Conducting CFD computations for partial domains of the reactor vessel not only reduces necessary computer resources, but also enables more detailed study of physical and numerical aspects as well as evaluation of the mesh size required in computation for the whole upper plenum and top core regions. Previous studies [6, 10] focused on base elements for either a 1/4 guide tube alone or a representative unit cell containing two quarters of the control rod guide tubes and one quarter of the support column. This study extends the computational domain to include multiple representative unit cells to capture any potential integral and multidimensional effects. A vertical slab cut from the center of the vessel to the outlet nozzle with the same width as the representative unit cell was modeled and analyzed. The commercial CFD code STAR-CCM+ version 4.06 is used to generate the computational mesh, solve the Reynolds-Averaged Navier-Stokes equations for incompressible flow with the realizable k - ε turbulence model, and post-process the results. Predicted velocity profiles are presented for different regions of the model, including the fuel assembly, top nozzle, guide tube, upper plenum and outlet nozzle regions. Predicted pressure distributions in various regions are also presented to indicate the driving forces for lateral flows.