Validation of STAR-CCM+ for bouyancy driven mixing in a PWR reactor pressure vessel

Within the OECD/NEA PKL-II project, experiments have been carried out aimed at investigating the flow mixing in the downcomer and lower plenum of a pressurized water reactor (PWR) in the buoyancy driven mixing regimes. The experiments have been performed at the ROCOM test facility, a 1:5 scaled representation of a KONVOI type pressurized water reactor (PWR). The facility is equipped with advanced instrumentation (i.e. wiremesh sensors) allowing a detailed measurement of flow mixing in the downcomer annulus and at the core inlet. A computational fluid dynamic (CFD) model has been developed at the Paul Scherrer Institute within the STARS project, employing the STAR-CCM+ code. The CFD model has been validated against the ROCOM experimental results. It has been shown that the developed model provided a good agreement with experiment. In order to evaluate the difference between momentum driven and density driven mixing regimes, calculations were performed assuming no density difference, and with 12% higher density in one of the loops respectively. (author)