Numerical modeling of flow induced vibration of nuclear fuel rods

Flow induced vibration (FIV) plays an important role in many industrial applications, including nuclear energy. In a nuclear power plant, several components could experience FIV. However, among them, fuel rods are critical because of the combined effects of very slender shapes of the rods and hydrodynamic loads induced by the turbulent flow of the surrounding coolant fluid. In this article, a numerical study of a nuclear fuel rod system is performed using a combined computational fluid dynamics (CFD) and computational structural mechanic (CSM) approach. The selected rod system is representative of an experimental set-up consisting of a single and multiple fuel rods exhibiting strongly coupled non-linear behaviors. As a first step, an operational procedure is proposed to construct a numerical model of the rod to be used in the Fluid-structure interaction (FSI) simulations. The material properties of the model are tuned to match the experimental natural frequencies measured in free air. Despite the structural complexities present in the experiments, the natural frequencies of the rod are correctly reproduced, which is an essential step for the subsequent FIV analysis. Subsequently, the FSI computations are performed and the numerical results are processed to extract the modal parameters of the system in axial turbulent flow regime. Both, one and two rod systems are extensively studied for different flow velocities. The obtained results agree with the measurements and the theory.