Numerical investigation on flow-induced vibration of LBE-cooled wire-wrapped rod and rod bundle

Abstract

Among the Generation-IV nuclear reactors, LBE-cooled reactors stand out as particularly promising due to their high neutron economy, high thermal conductivity, and high boiling point. However, the high density of lead-bismuth coolants and the mixing effect of helical structures lead to flow-induced vibrations, which can cause fuel rod vibrations leading to the leakage of radioactive materials and posing a significant threat to the safe operation of nuclear reactors. Consequently, this study employs CFD method to conduct an in-depth analysis of the flow-induced vibration characteristics of LBE-cooled wire-wrapped rod and rod bundles under various flow velocities to elucidate the intrinsic link between fluid excitation and structural vibration characteristics. Through multi-scenario analysis, this study not only clarifies the direct relationship between fluid excitation frequencies and fuel rod vibration responses but also integrates micro-scale fluid dynamic characteristics with macro-scale structural vibration characteristics, offering a novel perspective for understanding the physical mechanisms behind flow-induced vibrations. The results indicate that the main low-frequency components in the fluid excitation have induced low-frequency forced vibrations in the fuel rods that correspond to their response frequencies, which is consistent with numerous studies related to vibration. There is a significant difference in vibration behavior between single rod and rod bundle. As for rod bundle, due to the distinct pressure distribution characteristics of center channel and corner channel, the edge rods vibrate in diagonal directions and away from the center with a large amplitude, and the amplitude increase as flow velocity increases. However, flow velocity is not the definitive factor for vibration intensity. The vibration intensity and amplitude of the central rod increase as flow velocity increases, and fuel rods resonate in the studied flow velocities. In this study, not only the relationship between fluid excitation and structural vibration was revealed, but also the vibration characteristics of fuel rods are obtained. This provides a reference for further research and engineering applications in nuclear field.