Numerical Study on Effect of Clamping Failure on Flow Induced Vibration and Fretting Wear Analysis of Fuel Rods

 Flow elastic stability and vortex shedding were two important mechanisms for the flow induced vibration analysis. Due to the effects of manufacturing process, transportation and irradiation, the clamping action of grid on fuel rods may be invalid. Taking Type I and II fuel assemblies as an example, the effects of clamping failure on the natural frequencies, mode shapes, flow elastic stability and vortex shedding were studied. The results show that the effect of the dimple support failure on the natural frequency was directly related to the mode shape. The effect of the grid dimple failure near the original amplitude on the natural frequency was obvious. The effect of dimple failure on the natural frequency of two fuel rods was similar. For Type I, the velocity of flow at the top and bottom of the fuel rods were larger and the size was comparable. The dimple failure of the top and bottom grids had a significant effect on the stability of flow elastic and the vortex shedding ratio. For Type II fuel assembly, the dimple failure of the top grids had a more significant effect on the stability of flow elastic and the vortex shedding ratio comparing to the bottom grid failure.