Assessment of CFD Modeling for PTS Thermal-Hydraulics Using Multiple Scale Experimental Facilities

A serious threat to the life span of a Reactor Pressure Vessel (RPV) is the occurrence of Pressurized Thermal Shock during an Emergency Core Coolant injection in a loss-of-coolant accident (LOCA). Traditional thermal-hydraulic system codes fail to predict the complex three-dimensional thermal mixing and flow phenomena that occur during the injection. Since Computational Fluid Dynamics (CFD) is able to predict these phenomena, the present paper presents an assessment of Reynolds Averaged Navier Stokes CFD approaches. This assessment has been performed by comparing the numerical results obtained using advanced turbulence models available in the CFX 5.6 CFD code with experimental results of the full-scale Upper Plenum Test Facility (UPTF) and the 1:5 linear scale Rossendorf Coolant Mixing Model (ROCOM). The assessment shows that the observed flow behavior is quite similar for these facilities of different scale. The CFD code is very well capable of capturing the stratification and mixing phenomena occurring in the cold leg, while it has been shown that current RANS approaches are less capable of grasping the complex oscillating flow in the downcomer. (authors)