Prediction of light gas distribution in experimental containment facilities using the CFX4 code

Two- and three-dimensional simulations of experiments on atmosphere mixing and stratification in a nuclear power plant containment were performed with the computational fluid dynamics (CFD) code CFX4.4. Experimental data were obtained from the Institut de Radioprotection et de Sureté Nucléaire (France), where experiments on the TOSQAN facility were performed, and from Becker Technologies GmbH (Germany), where experiments on the ThAI facility were performed. The fluid inside the vessels was modeled as a single-phase gas atmosphere, and simple models for steam condensation on structures and in the atmosphere were introduced. The purpose was to assess the applicability of the CFD approach to simulate the behavior of light gases in containments at accident conditions. The comparisons of experimental and simulated results show that, despite a tendency to simulate more intensive mixing, the proposed approach may replicate the structure of the atmosphere reasonably well.