A Modal Analysis Procedure for PWR Fuel Assemblies

Abstract

The analysis of vibration effects on the structure of Nuclear Fuel Assemblies was performed by using a 3-D finite element model. A 16×16 Standard Fuel Assembly design was used for this analysis. Since fuel assemblies have a nonlinear behavior during normal operation, due to the interaction between fuel rods and spacer grids, the methodology consisted basically of four steps: a modal analysis for obtaining the natural frequencies, a linear structural analysis for the no sliding stiffness calculation, a nonlinear structural analysis for the sliding stiffness calculation, and a correction factor estimate for natural frequencies obtained directly from the modal analysis. Also, it includes the major calculated stresses associated with the most external thimble tube.