Evolution of grid-to-rod fretting of nuclear fuel rods during burnup

Nuclear fuel rod consists of the cladding and fuel pellets stack. Fuel rods are mounted in fuel assemblies and they are linked by spacer grids. Due to vibration of a fuel assembly during the reactor operation, grid-to-rod fretting (GTRF) occurs in contact points between the cladding of the fuel rod and spacer grid cells. The GTRF phenomenon causes the loss of mass of the cladding in contact points and it can possibly lead to leakage of fission products into a coolant. The paper presents a complex modelling concept for the GTRF analysis of fuel rods due to vibration caused by pressure pulsations of the coolant. The method deals with several essential subproblems. The key part of the method is a dynamic model that simulates vibration of the fuel rod. To estimate wear properties of the cladding, an experimental procedure is used and to determine the state of burnup, a physical model is used. Based on the simulated vibration of the fuel rod and the subsequent GTRF analysis, the evolution of the GTRF during burnup can be determined.