Simulations of Basic Gas Mixing Tests With Condensation in the PANDA Facility Using the GOTHIC Code

In the framework of the OECD SETH project, a number of experiments related to safety issues in the containment of a nuclear reactor have been performed in the large-scale facility PANDA. The tests have been designed to provide an adequate database for basic assessment of CFD and advanced lumped parameter (LP) codes. The test geometry consists of two interconnected vessels (compartments) with fluid injected in one vessel. The gas distribution in the injection vessel and the distribution of gases and the propagation of the stratification in the adjacent vessel are measured. Four of these tests were performed with initial and boundary conditions that resulted in substantial condensation rates. Three of these experiments featured vertical injection (with production of a plume), and in one, the transient response due to a high-momentum horizontal injection (jet) was investigated. The injected fluid was either saturated steam or a superheated mixture of steam and helium, and the fluid initially present in the vessels was pure air. These experiments have been analysed with the advanced containment code GOTHIC, and the main results are presented here. In general, the results obtained with the code and the standard mesh were in good agreement with the data. Limitations in modeling local phenomena controlled by complex flow patterns (e.g. heat transfer in the region of an impinging jet) and the need for refined meshes to reproduce certain aspects of the transients (e.g. erosion of the interface between layers of different gas composition) were also identified.