Post Test CFD Calculations of Experiments at the ROCOM Mixing Test Facility related to Boron Dilution and Cold Water Transients

The temperature and boron concentration fields established by the coolant mixing during nominal and transient flow conditions in the reactor pressure vessel of the PWR Konvoi were analyzed by numerical and experimental studies. The validation of the CFD results (CFD-code CFX-4) was carried out at the Rossendorf mixing test facility ROCOM. ROCOM is a 1:5 scaled Plexiglas model of the PWR Konvoi allowing velocity measurements by the LDA technique. Plugs of coolant with low boron acid concentration and/or different temperature are simulated by salt water injection. The CFD calculations were based on the assumption of incompressible turbulent flow. The turbulence was considered by an k--model. The perforated drum, as well as the reactor core with core internals, were represented by the model of a porous body. Calculations were performed for constant flow in the loops as well as for the scenario of an onset of the circulation. For transient CFD-calculation sensitivity studies were performed to check the numerical diffusion and the choice of different turbulence models.