Nonlinear Vibration of Nuclear Fuel Rods

Abstract

From mechanical point of view, nuclear fuel rod (FR) is a complex system consisting of two subsystems—fuel rod cladding (thin walled zirconium tube) and a fuel pellets stack placed inside the cladding placed with a small radial clearance. Both subsystems are beam-type continua that possibly impact-interact during the vibration caused by fuel assembly support plates motion. The FR is supported at eight levels by prestressed spacer grid cells. The paper focuses on complex mathematical modelling of such a system including all the nonlinearities given by possible impacts between cladding and fuel pellets stack and possible loose of contact between cladding and spacer grid cells due to low prestress. In all the contact points, friction-vibration interactions respect three possible phases—stick, slip and separation—depending on the slip velocity and normal contact force. The model is used for estimation of a fretting wear of the cladding in contact with spacer grids.