Experiments and CFD model development for wall condensation on containment structures
The three-dimensional flow and transport processes in the containment are increasingly described with CFD (Computational Fluid Dynamics) models. A reliable prediction of the pressurization and hydrogen distribution, as well as the natural convection flows, the gas transport and the local condensation rates is safety-relevant with regard to the integrity of the containment as the last barrier against the release of radioactive substances into the environment. A high spatial grid resolution of the CFD model in the boundary layer for resolving the near-wall transport processes and buoyancy forces is required to determine their potential influence on the condensation rate. Existing wall functions that could enable a less expensive treatment reveal significant model deficits and thus require extension. The primary objective of the project is to extend the database on near-wall transport processes in wall condensation, which was already obtained in previous projects (SETCOM 150 1489) at the SETCOM test facility, and to extend and systematically validate the newly developed model approach. The development of a model basis is conducted in the open source CFD software package OpenFoam. The overall objective is to allow for an efficient and reliable representation of wall condensation in a full-scale CFD simulation of the containment. This will increase the reliability of accident analyses, especially with regard to hydrogen distribution, such that improved statements on the load of the containment due to short-term (H2 combustion) and long-term pressurization (steam and H2/CO/CO2 release) as well as the efficiency of passive safety systems in the process of postulated accident scenarios. The constant development of the codes requires a continuous validation. For this purpose, increasing demands are being placed on the corresponding experiments, especially in the CFD model development, both with regard to instrumentation and with regard to execution and evaluation. The SETCOM2 experiment, designed with the focus on CFD development, enables these requirements to be fulfilled.