Dynamics of frictional interaction of a fuel rod cladding and spacer grid cell in a fuel assembly

摘要

The subject-matter of the study are the processes of friction in the fuel assemblies of pressurized water reactors.The friction forces influence the process of fuel assembly (FA) assembling at the manufacturer, the ability of reactor core to be assembled, FA vibration strength in the course of operation, serviceability of control rods of the reactor trip system, FA resistance to longitudinal- transverse thermal-mechanical bowing. The links by elasticity and friction forces in the "fuel rod-to-spacer grid" mating units change considerably due to effect of temperature, irradiation and time on the FA, and time history of the change in these forces influences greatly the FA operational properties. There were few studies on the friction of zirconium alloy components. The friction processes were the direct cause of FA failures in Russia and abroad by the mechanisms of fretting-corrosion, spacer grid warping, thermo-mechanical bowing of FA and sticking of reactor trip system control rods.The study of friction processes between the standard specimens of fuel rod claddings and fragments of spacer grid (SG) cells was performed under translational and vibratory motion in air at 20 °C, and the effect of surface conditioning of fuel rod claddings (anodization, etching, grinding, oxidation), and of contact geometry of bulges on the friction characteristics was determined.The main friction coefficients were defined and the coefficients of friction between the SG cells and fuel rod claddings were determined in variation of the normal force value in the contact, the rate of mutual displacement, geometry of SG cell and the states of contact surfaces characterizing with different surface conditioning and degree of wear. The main friction mechanisms are accompanied with a full (friction coefficient is 0,5-0,8), or partial (friction coefficient is 0,2-0,5) contact of pure mechanical surfaces and the contact of the surfaces with strong protective films with the friction coefficient 0,1-0,2. Keywords: reactor, fuel, rod, zirconium, coefficient, friction.