CFD simulations of cross-flows along in-line and staggered tube bundles which emulate those encountered in the calandria of CANDU-6 reactors are presented. The knowledge of external wall temperature distributions around calandria tubes is a major concern during normal and off-normal operating conditions of CANDU reactors. Calculations are performed using the FLUENT software with several turbulence models using segregated and Coupled algorithms. It is observed that κ-based models are able to reproduce mean velocities in staggered bundles. In most cases, the Coupled algorithm yields convergence even if it requires a longer computational time. Based on this work, the standard κ-ε model is recommended to perform this kind of simulations. Improved κ-ε models do not lead to better results while the κ-ω model predicts very well the physics only around the first row but it is unable to predict the flow around tubes located far downstream in the bundle.