Study of Fuel Rod and Grid Supports Interaction

In order to predict the dynamic response of a nuclear fuel rod and its supports (spring and dimples) a non-linear model has been developed. The non-linearities arising from the supports are defined as a function of the rod motion and incorporated in the differential equation as generalized pseudoforces. This approach allows the use of modal analysis and preserves the physical understanding of rod frequencies and modes. The modal equations were written with the help of the Laplace transformation and integrated using an Ordinary Differential Equation (ODE) solver. The model determines the rod natural frequencies and motion, the support impact forces and the normal work rate. The paper describes the model predictions for a single span rod and compares them to experimental data.