A parametric study has been performed using STAR-CCM+ computational fluid dynamics tool to investigate the differences in global quantities that characterize in-vessel transient mixing flow when several URANS turbulent models are employed. The numerical models represent a four loop KONVOI type reactor pressure vessel and the selected transient wants to estimate the effectiveness of the cold leg emergency core coolant injection in restoring proper operating conditions of the residual heat removal system. During the OECD-NEA PKL 3 project, the scenario has been chosen as analytical benchmark for computational fluid dynamics and thermal hydraulic system codes and the experimental data have been collected at the Rossendorf coolant mixing facility (ROCOM).
In the paper a direct comparison of the numerical results and experimental data is performed. Results show that the different turbulent models predict the mixing in the downcomer, core inlet and in the cold leg far downstream the emergency core coolant injection. However upstream the injection point, where counter-flow occurs, the turbulence models predict a rather different behavior of large unsteady structures. Moreover, numerical results show quantitatively good agreement with the experiments in the cold leg region, whereas a rather large under prediction of the flow tracer concentration is observed in the downcomer and at the core inlet.