Advanced three-dimensional (3-D) computational tools are increasingly being used to simulate complex phenomena occurring during scenarios involving operational transients and accidents in nuclear power plants. Among these scenarios, one can mention the asymmetric coolant mixing under natural-circulation flow regimes. This issue motivated some detailed experimental investigations carried out within the Organisation for Economic Co-operation and Development/Nuclear Energy Agency PKL projects. The aim was not only to assess the mixing phenomenon in the reactor pressure vessel but also to provide experimental data for computer code validations and more specifically thermal-hydraulic system codes with 3-D capabilities. In the current study, the ROCOM/PKL-3 T2.3 experimental test is assessed using, on one hand, thermal-hydraulic system codes with 3-D capabilities and, on the other hand, computational fluid dynamics computational tools. The results emphasize the capabilities and the differences among the considered computational tools as well as their suitability for such purposes.