The colloquium starts with a brief presentation of EDF R&D and its Fluid Mechanics, Energy and Environment Department. Then, after an overview of the main numerical tools utilized in different fields, the talk focuses on the use of Code_Saturne, EDF in-house and open-source computational fluid dynamic (CFD) software, in nuclear engineering applications. First, an introduction to turbulence modeling is given through the concepts of (U)RANS (unsteady Reynolds-averaged Navier-Stokes) and LES (large eddy simulations). Then, the presentation promotes some ideas and guidelines one should keep in mind while running CFD simulations with these turbulent models. The illustrations addresses the use of Reynolds stress models for complex flows, modeling turbulent heat fluxes, wall resolved models vs. wall modeled in RANS, mesh refinement criteria in LES… Application of the most accurate approaches in turbulence modelling: DNS (direct numerical simulation) and wall resolved LES for the understanding of flow and RANS validation is finally encouraged.