The paper presents the results of numerical analysis on the local and global internal flow behaviour at the inlet of the vaned diffuser of a radial flow pump model, taking into account the effect of fluid leakages for various flow rates and a given rotation of speed. For each flow rate, numerical calculations were performed both with two different boundary conditions: - Without any leakage effects. - With calculated leakage effects The numerical simulations were realized with the two commercial codes: i-Star CCM+ 8.02.011 (at LML), ii-CFX 10.0 (at University of Padova). RANS unsteady calculations, with a k- RNG model were performed with Star CCM+. Fully unsteady calculations of the whole pump were done with CFX with DES turbulent method (Cavazzini [1]). For each flow rate, different angular positions of the impeller are considered. First part of the paper shows global comparisons between numerical and experimental results already presented in ref [2-3], for which the effects of fluid leakage due to the gap between the rotating and fixed part of the pump model were found to be interesting to be analysed. Second part is devoted to the local comparisons of flow structures at the inlet section of the diffuser, without and with leakages only with Star CCM+.