Effects of spacer grid's stiffness on vibration characteristics of a PWR fuel rod

In a PWR assembly,fuel rods and control rods excited by surrounding coolant flow and supported by grillwork at intervals can be simplified to multi-span continuous beams.According to the actual operating state,a 2D model of a rod and grid system was studied,and a relation between the equivalent stiffness of the spacer grid and the 1st nature frequency of the fuel rod was established.Consequently,the equivalent stiffness of the grid could be identified with the measured natural frequency of the rod.Compared with the numerical solution using ANSYS,it was shown that the proposed method identifying the equivalent stiffness of a spacer grid based on the vibration theory of a multi-span continuous beam is resonable and effective.Then,the dynamic characteristic analysis of the fuel rod was conducted.