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[en] During their operation in a Pressurized Water Reactor (PWR), fuel assemblies are exposed to intense hydraulic forces (axial and lateral) that must be taken into account in the design of the fuel assemblies and the vessel internals as well. The net upward hydraulic force, referred to as the lift force, is the result of the axial flow interacting with hydraulic resistances of the fuel assemblies. Related to it, one fuel design criterion that must be verified is that the fuel elements must rest on the lower plate of the core under all Condition I and II events, except in the case of Hot Pump Over-speed (HPO). In addition, hydraulic forces, both axial and lateral, can result in vibrations and contribute to the assembly bow. To calculate the hydraulic forces, ENUSA is developing, together with Westinghouse, a three dimensional (3D) calculation model based on the thermalhydraulic (T/H) code, VIPRE, which accounts for effects of pressure and flow distributions in the reactor core. The 3D core model solves the linear momentum equation for each fluid control volume containing one single fuel assembly using local fluid conditions calculated by VIPRE. Hydraulic forces are obtained for all the fuel assemblies in a PWR core for different core loading patterns and operating conditions. The calculation model is being qualified with respect to measurements of flow distributions in PWR fuel assemblies in hydraulic test loops, comparison with results from other reactor core T/H design codes, model sensitivity studies, and calculations with Computational Fluid Dynamics (CFD) codes. This paper describes the model development approach, the details of the 3D calculation model and the qualification results.