Validation of a Simple Condensation Model for Simulation of Gas Distributions in Containments with Cfx

In cooperation with other institutions, GRS adapts and validates the CFX code developed by ANSYS for LWR containment applications. In a severe accident scenario in a LWR large amounts of steam and hydrogen are released into the containment at different locations. To simulate the main phenomena relevant for accident scenarios within LWR containments models, especially the ones provided to CFX by the users have to be validated. A simplified wall and bulk condensation model was implemented by GRS in CFX using USER-FORTRAN routines and has been validated by simulating several experiments where condensation processes are significant. The main focus of this paper will be on the simulation of the experiments Panda4 and Panda4bis performed at the Paul Scherrer Institute. These experiments differ only in temperature boundary conditions; hence condensation occurred in Panda4bis only. For the simulation of the Panda4 experiment a grid sensitivity study was performed and the influence of the turbulence model and other parameters like turbulence intensity of the inflowing steam were investigated. CFX is able to simulate very well the flow pattern of the experiment with the counter current in the connecting pipe between the two Panda vessels and the steam distribution. The developed model for the wall and bulk condensation was validated by calculating the Panda4bis experiment using similar models as for Panda4. The influence of the mesh resolution near the vessel walls was investigated, because this is a critical parameter for the condensation model. Some model shortcomings lead to larger deviations from experimental data than in simulating Panda4, but in general the simulation results are satisfactory.