The proposed contribution is dedicated to numerical methods for solving strongly coupled fluid–structure dynamic problems where the complexity of the structures and the reduced remaining fluid volume do not allow to handle their exact geometry. Porous approaches are preferred instead but it is mandatory to go beyond classical techniques to account for inertial and convective components of the flow, as explicitly required by the application of the methods to the dynamics of a set of pressurized water reactors fuel assemblies under axial flow and seismic‐like loading. A new computational framework is thus introduced with special care given to stability, robustness, and computational efficiency of the coupled solver. Comparisons with well‐chosen experimental results provide some valuable validation of the numerical methods and demonstrate the ability of the model to reproduce the hydraulic coupling between several fuel assemblies.