CFD simulation of the Vattenfall 1/5th-scale PWR model for boron dilution studies

The VATT-02 experiment, performed at Vattenfall, Sweden, with a 1/5th-scale model of a 3-loop PWR pressure vessel, has been simulated with the computational fluid dynamics (CFD) code CFX-5 at PSI, Switzerland. The simulations were initially part of the FLOMIX-R EU 5th Framework Programme, aimed at providing validation data prior to CFD codes being used to model full-size nuclear vessels. These studies were extended at PSI to examine mesh effects. Steady-state velocities and transient boron concentration distributions were plotted, and their sensitivity to different CFD models and mesh refinement examined. Steady-state velocities in the downcomer were not in good agreement with experiment at all instrumentation locations, but, nevertheless, predicted transient boron distribution and its minimum concentration at the core inlet were close to the measured data. Useful conclusions could be drawn for application to full reactor size.