CFD simulation of a fuel assembly under imposed seismic motion

In the context of evaluating the dynamic behavior of Pressurized Water Reactor (PWR) fuel assemblies, this study conducts a comprehensive parametric investigation of fluid–structure interactions using a geometry representative of an ICARE/EUDORE-type assembly. The simulations were performed using the TrioCFD solver, with a focus on understanding how imposed structural motion affects the assemblies under various flow and vibration conditions, specifically examining the effects of axial flow velocity, vibration frequency, and amplitude. The fluid domain was modeled using the Reynolds-Averaged Navier–Stokes (RANS) equations with a standard k - ϵ turbulence model. A high-resolution mesh, comprising approximately 76 million elements with near-wall refinement, was utilized to capture the flow physics under experimentally relevant conditions. To reduce computational cost while preserving accuracy, the spacer grids were modeled using a porous medium approach. The pressure-loss coefficient was calibrated against experimental data and validated on the full assembly. A test matrix spanning four flow velocities, three vibration frequencies, and three amplitudes was developed. From these simulations, time-resolved velocity fields and hydrodynamic forces on the structure were extracted. For the first time, modal added-mass, damping, and stiffness coefficients were computed from numerical simulations on a geometry representative of a full-scale PWR fuel assembly. The findings provide new insights into fluid forces acting on a fuel assemblies under operational conditions. Additionally, they offer a numerical framework for enhancing or developing reduced-order mechanical models applicable to reactor core design and seismic safety assessments.