Numerical computations of moderator flows inside calandria of the typical CANDU-6 reactor are presented here. The numerical model is based on incompressible Navier-Stokes equations in artificial compressibility formulation with dual time-stepping approach for time-accurate computations. A high-resolution unstructured finite-volume scheme, based on the HLLC-AC Riemann solver for convective fluxes and central differencing type discretization for viscous fluxes, is used here. In order to simulate more realistic flow, the calandria tube matrix is considered directly, in contrast with the usual practice of indirect accounting of tube bundles through porosity modeling. The moderator flows are computed for different operating conditions. The nature of computed flow is found to be dependent on the relative balance between momentum and buoyancy forces as observed by Carlucci. A parametric study is also carried out to investigate the effect of moderator inlet diffuser location, moderator inlet flow velocity, and angle of moderator inlet diffuser. The inlet flow velocity and inlet diffuser location are found to have significant effect on flow features inside the calandria.