CFD evaluation of turbulence models for flow simulation of the fuel rod bundle with a spacer assembly

Computational fluid dynamics (CFD) is increasingly being used in nuclear reactor safety (NRS) analyses to describe safety-relevant phenomena occurring in the reactor coolant system in greater detail. This paper presents the results of numerical issues such as mesh refinement, wall treatment and appropriate definition of boundary conditions, which exert great influence on the results of a CFD simulation. A high quality computational mesh was used to investigate the choice of turbulence model appropriate for the complex swirling flow in the rod bundle subchannels. The performance of various turbulence models are evaluated by calculation of the Nusselt number distribution in a fuel bundle. Comparison between numerical and experimental results of lateral and axial distributions for the Nusselt number obtained via turbulence model without near-wall functions is not sufficiently good, while agreement is found between the computational simulation of the realizable k–epsilon model with near-wall functions and the experimental measurements, for locations close to the support grid. As a result of this study, we have been able to determine the most appropriate turbulence models and the best enhanced wall treatment for modeling reactor coolant systems.

► We model water flow through the rod bundles of a nuclear reactor’s cooling system.
► We evaluated different models to determine which maximize the simulation accuracy.
► Using enhanced wall treatment significantly improves the accuracy of the results.