Thermal Hydraulic Analyses for PTS Evaluation: Comparison of Temperature Fields at RPV Predicted by System TH Code and CFD Code

The paper describes methods used for evaluation of pressurized thermal shock (PTS) at UJV Rez and selected results. The UJV Rez participated on the one hand in a number of international programs focused on development of PTS methodology, benchmark testing etc. On the other hand UJV has worked in several projects evaluating PTS for nuclear power plants in the Czech Republic and abroad. The introductory part of the paper also briefly mentions a development of PTS methodology in the world, its current status and trends. The core of the paper describes thermal hydraulic part of the PTS evaluation process, which usually contains system thermal hydraulic (TH) analysis and mixing calculation. Already at the system TH calculation level, a simple 2D model of reactor downcomer (DC) is used in UJV Rez analyses — as this approach enables the prediction of 2D temperature and velocity fields in DC and improves the prediction of natural circulation flow or its stagnation in individual loops. For the subsequent mixing calculation the Computational Fluid Dynamics (CFD) computer codes are used nowadays. Comparison of 2D temperature fields from 2D system TH analysis and CFD calculation shows surprisingly good agreement for most cases. The paper shows such comparison for several representative cases and takes a more detailed look into one of them.