Flow-Induced Vibration And Fretting Wear Of Reactor Fuel Rods

The fuel rods in axial flow are susceptible to vibration induced by external fluid forces,which can cause fuel rod deformation and even micro-motion wear on the contact surfaces to accelerate the fatigue failure of fuel rods,posing a major hazard to reactor safety.The study of fuel rod bundle rheological vibration and micro-motion wear in axial flow can help to understand the vibration pattern of fuel rods and optimize the structural design of fuel rods to reduce the vibration hazards,and predict the fatigue failure location to ensure the core safety.In this paper,the modal analysis of the fuel rod is first conducted to calculate the inherent frequency and damping ratio of the fuel rod at each order,and to learn the basic structural dynamics of the fuel rod.Before conducting the analysis of fuel rod vibration response in axial flow,the numerical calculation method used is compared with the results of published experimental literature to verify the feasibility of the numerical analysis method,and then numerical calculations are performed from the effect of different inlet flow rates on the fuel rod vibration response.It is found that the inlet flow rate has a great influence on the vibration response of the fuel rod,and the larger the inlet flow rate is,the larger the vibration amplitude and the more violent the vibration is.The power spectral density(PSD)analysis was also performed on the fuel rod vibration displacement time course,and it was found that the frequencies corresponding to the maximum vibration energy were mainly concentrated near the first-order intrinsic frequency,so the first-order modal characteristics play an important role in the fuel rod vibration.Then,on the basis of the vibration characteristics of a single fuel rod,the axial flow vibration response of the fuel rod bundle was analyzed,and the effects of vibration on the flow field characteristics,the vibration response of the bundle for different inlet flow rates,and the vibration response of the bundle with and without the positioning grid were investigated.The vibration amplitude of the fuel rod bundle is larger than that of a single rod because the interaction between the bundles enhances the vibration intensity of the bundle as a whole,and the vibration amplitude of the fuel rods in different arrangements in the bundle also differs greatly.Finally,a micro-motion wear model of a single fuel rod with a positioning grid was constructed,and it was found that the wear depth and shear stress increased with the increase of cycle times,and the two showed a positive correlation.The fatigue failure was predicted by applying the multi-axis fatigue critical surface criterion,and the possible location of fatigue failure was predicted roughly aroundX_d.