Vibrational Behaviour and Natural Frequencies of a CANDU Fuel String

Abstract

Inside a pressure tube drag force induced by the coolant flow couples the motion of individual bundles and forms a fuel string. In this paper, dynamic behavior of a Candu fuel string consist of several bundles is investigated. A comprehensive dynamical model is presented to handle vibration a string of 12 CANDU6 fuel bundles inside a pressure tube under operating conditions. A finite element based computer program is developed at Ryerson University in collaboration with Candu Energy Inc. to simulate fuel string vibration and vibration induced wear in the pressure tube. Contact constraints between neighboring fuel elements, between fuel elements and pressure tube and between neighboring bundles are considered in this study. All the solid components are discretized in space domain by the means of finite element method. Bozzak-Newmark integration scheme is employed to discretize the system equations of motion in the time-domain. The complex non-linear fuel string problem is formulated to be a Linear Complementarity Problem (LCP). Fuel string is excited, FFT analyses are performed and natural frequencies of the systems are extracted.