On the factors affecting the fretting-wear risk of PWR fuel assemblies

Key factors affecting the rod-to-grid fretting-wear risk of fuel assemblies operated in pressurized water reactors (PWR) are evaluated. The analysis is part of a comprehensive approach to predict fretting-wear risk based on the fuel assembly operating conditions. The assembly wear damage is determined by a non-linear vibration model of the nuclear fuel rod exposed to a turbulent flow. The study evaluates the sensitivity of the wear damage to the grid support forces, fuel rod-to-grid gap size, assembly grids misalignment, rod structural damping and stiffness, assembly bow shape, friction coefficients and turbulence force spectrum. The results of the numerical simulations show that the grid cell clearance and the turbulence forces are key factors in the wear process. Since a good correlation exists between these two parameters and the assembly location in the core, it is recommended to include consideration of the wear risk minimization as an additional criterion for the design of the core loading pattern.