Simulation of three-dimensional mixing phenomena in nulcear reactor containments

The objectives of the project were: Further development and validation of the ANSYS CFD software for simulating single and multi-phase transport phenomena, mixing and condensation of steam in reactor containments; Further development and validation of ANSYS CFD's Burning-Velocity Model (BVM) for simulating unsteady-state chemical reactions of hydrogen-air mixtures; Reduction of the high computing times for unsteady-state three-dimensional flows in reactor containments; Provision of models and workflows for simulating the effects of opening and closing doors and flaps in reactor containments; Validation of the developed models and algorithms by simulating condensing flows measured in the ThAI facility of Becker Technologies; All work items were successfully completed: Single- and two-phase flow models for simulating volume and wall condensation were developed and validated. The single-phase models show high computational efficiency at acceptable accuracy. For higher accuracy requirements the more compute-intensive two-phase flow model can be used. The models were first tested for laboratory-scale experiments and then for large-scale experimental facilities. The project partner GRS has used the models for simulating condensing flows in a generic reactor containment of Konvoi-type. In the second work item the Burning-Velocity Model was extended to consider effects of ballast steam during hydrogen combustion. ThAI experiments served as validation test cases. The validation yielded partly good and partly less satisfactory agreement with data. Explaining these differences would entail use of more advanced turbulence and reaction models and additional measurements. Various combinations of pressure-velocity coupling algorithms and variable storage schemes were investigated in order to see their influence on computing times. One result was that cell-centred variable storage offers advantages in terms of computing times for unsteady-state flows. In addition, extrapolation techniques and adaptive time-stepping schemes were tested. The latter technologies can both contribute to a sizable reduction of computing times. Three methods for opening and closing doors in reactor containments were developed and tested. The best results were obtained with the Multi-Domain-Model which builds upon the Generalised Grid Interfaces of ANSYS CFD. The algorithm was tested for various cases and has been successfully used by the project partner GRS to simulate flows in a generic reactor containment of Konvoi-type. Finally, different test cases measured in the ThAI facility were investigated. Geometry models, meshes, boundary condition files and control parameters were provided to the project partners. The MiniPanda benchmark and the ThAI TH26 benchmark were also supported as part of the present project.