Numerical investigations on flow-induced vibration of fuel rods with spacer grids subjected to turbulent flow

Fuel rods, one of the most important parts in the nuclear reactor core, are usually supported by spacer grid along the axial flow direction. Since those fuel rods are surrounded by high-velocity coolant, vibration will be induced, termed flow-induced vibration (FIV). The resulting oscillations may cause abrasion of the cladding, known as fretting wear. In order to predict this fretting wear more accurately, it is essential to study the vibration characteristics. In this paper, numerical simulation is carried out to investigate the interaction of fuel rods embedded in a spacer grid with mixing vane subjected to strong turbulent flow. The flow-induced vibration of fuel rods and the surrounding components are analyzed and reported in detail. It is found that the vibration is dependent on several parameters, such as wall shear forces and pressure. However, the fluid force acting on the fuel rod is mostly due to the pressure. The flow velocity has a significant influence on the flow-induced vibration in axial turbulent flow. The vibration of fuel rod is very weak when the flow velocity is low. The numerical method applied in this paper can be used to predict the vibrations of the fuel rods accurately and this will be useful for the further fretting wear evaluating, which should be helpful in the design of fuel assemblies.