Theoretical investigations on flow-induced vibration of fuel rods with spacer grids in axial flow

Abstract

Fuel rods, one of the most important components in the nuclear reactor core, are usually supported by spacer grids along the axial direction. Since those fuel rods are long and slender, flow-induced vibration (FIV) will be induced and cause abrasion of the cladding in the axial flow of high-velocity coolant. A theoretical study applying modal analysis method and power spectral analysis method is carried out to analyze the vibration characteristics and FIV root-mean-square (RMS) response of fuel rods. In this study, a fuel rod with spacer grids is modeled as one dimensional multi-span beam and the fluid force along the fuel rod is considered as random impulsive load. The influences of span length, the axial flow velocity and the correlation length coefficient of axial flow on FIV response displacement of fuel rods are studied. The sensitivity analysis results reveal that the FIV of fuel rods has strong negative correlation with span length, while it is positive by related to the axial flow velocity and correlation length coefficient.