One of the most important parameters in the analysis of containment safety of the light water reactors during a loss of coolant accident (LOCA) is the prediction of the hydrogen concentration. To ensure proper design of the containment to mitigate the fire/explosive risk created by the flammable hydrogen gas, this concentration build up must be analyzed. Lumped parameter (LP) codes are the main tools used in containment thermal-hydraulic analysis. However, they are limited when it comes to scenarios which require higher fidelity analysis of local phenomena. While the use of computational fluid dynamics (CFD) allows for higher fidelity analyses, CFD requires a comprehensive validation study due to turbulence and condensation modeling.
During a LOCA accident, the leaked hydrogen from the primary circuit can form a stable stratified layer at the top of the containment building. The formation and erosion of a stratified layer is a challenging numerical problem due to the interaction mechanism of the jet flow with the stratified layer. The OECD-NEA conducted an experiment at the Paul Scherrer Institute (PSI) as a part of the third International Benchmark Study (IBE-3) to investigate the erosion of the stratified layer by a vertical air-helium jet from the bottom of the large vessel. During the experiment, CFD grade experimental data was generated that could be used for comparative studies.
In the present study, the experiment is simulated by using the STAR-CCM+ CFD code with various turbulence models including Reynolds-Averaged Navier-Stokes (RANS) models and Large Eddy Simulation (LES). The Realizable k-? and k-? SST showed good agreement with the experimental when predicting the erosion of the stratified layer and global mixing of the gas components. The LES model also showed good agreement for velocity and faster erosion with experimental data, while the cost of the LES simulation was much higher than RANS simulations. The current validation study contributes to the sensitivity analysis of the turbulence models for erosion behavior in the stratified layer. In addition to that, the results of this study will provide a foundation to discuss the feasibility of the CFD code usage in containment level thermal hydraulic analysis.
