Numerical investigation of the modal characteristics for a VVER-1000 fuel assembly

摘要

In this research, we focus on a numerical investigation conducted on the Fluid-Structure Interaction (FSI) of a VVER 1000 fuel assembly to determine frequencies of fuel roads, a key variable on fretting wear. To consider the effect of the Spacer Grids (SGs), a new approach based on a symmetrical alignment of the fuel rods and SGs is used to determine local SG cell's stiffness. Also, a source term in the streamwise direction is added to the momentum equation to consider the pressure drop due to SGs presence. The first part of the paper compares the natural frequencies of the single unsupported fuel rod, the SG reinforced fuel rod and fuel rods with fixed supports. Calculation of natural frequencies from modal analysis shows the existence of a spectrum of frequencies for the SG stiffened fuel rods. In the second part, the fundamental mode characteristics of the fuel rods due to Flow-Induced Vibration (FIV) are calculated. To this end, a proper fluid domain is used based on the lateral velocity criterion to consider the effects of added mass in a confined flow. Also, the shear-stress transport (SST) k-omega turbulence model is used to include the impact of the Reynolds stresses. The fundamental mode's frequencies calculated about 69-72 Hz and are in good agreement with the experiment.