Leakage flow implementation in a porous media modeling for fluid–structure interaction in PWR fuel assemblies

The proposed article addresses the complex issue of fluid–structure interaction (FSI) in Pressurized Water Reactors (PWR) fuel assemblies under dynamic excitations. The study focuses on modeling leakage flow in porous media, crucial for understanding fuel assembly behavior during seismic events. The paper aims to model strongly coupled FSI in congested media like PWR fuel assemblies, where traditional models like Darcy’s law are insufficient. The approach involves filtering local fluid equations, designing a structural model, coupling fluid and structural variables, and solving the coupled problem numerically. The study extends an existing methodology validated for the dynamic response of PWR fuel assemblies under axial flow and external loading. The research introduces a leakage flow model to account for gaps of variable thickness between fuel assemblies. The porous medium approach defines an equivalent fluid model over the entire space occupied by the fuel assemblies, providing equations for equivalent velocity and pressure, and forces applied by the fluid onto the structure. The by-pass model considers the fluid domain between fuel assemblies, assuming a flat planar shape of variable thickness. The Navier–Stokes equations are integrated over the by-pass thickness to derive governing equations for the flow. The discrete problem is solved using finite element methods, with time and space discretizations for both the porous medium and the by-pass models. The solution involves iterative procedures to handle the coupled fluid–structure problem. The model is validated through tests and comparisons with experimental, including data from full scale tests on the HERMES facility, demonstrating its ability to capture key physical phenomena. The study successfully validates the wall by-pass model, showing satisfactory results without calibration, relying solely on geometric parameters. Future work could extend the model to include corner by-passes and refine grid effects. • Two new models, for flow between fuel assemblies are proposed. • Numerical implementation is proposed to handle the nonlinear coupled problem. • Validity of the model is supported by experimental comparisons.