Pressurized Water Reactor Fuel Rods Flow Induced Vibration Simulation Research

Fuel rods and fuel assembly are key components in a reactor, serving as the first safety protection, the life and reliability of which are important factors to improve safety and economization in nuclear power industry. PWR rods receive wear from grillwork that supports them, due to vibration caused by unsteady coolant flow. Lately, the flow induced vibration analysis of fuel rod has been a hot spot. In this thesis, a single fuel rod is studied, and a mode of it is established. After an important parameter is identified using experiment data, the dynamical response of the fuel rod in coolant flow can be obtained.In this thesis, first, we study a2D model of rod and grid system, and sets up a tie between equivalent stiffness of spacer grid and1st frequency of the fuel rod. Consequently, the equivalent stiffness of the grid can be identified according to experimental data. The vibration analysis of the rod can be processed once the method of identification’s been proved valid, in contrast to ANSYS’results.Secondly, in order to made dynamic analysis of fuel rod in coolant flow, Fourier series method is introduced and applied, based on Stokes’ transformation, which leads to an eigen equation, and frequencies and modes are given. Results of this method are compared to classical analytic method and Ansys’, which proves an unassailable validation. Then we made a presumption that fluid and fuel rod are weak-coupled system, and added-mass of fluid on the rod can be obtained.Thirdly, we assume that fluid takes effect in2main ways:steady flow convert to added-mass on the rod, while turbulent flow is exerted on the rod as a spectrum excitation. Using spectrum analysis tool of Ansys, we have the vibration performance of fuel rod, which provide advice in avoiding wear between fuel rod and grid. The innovation of this thesis lies in:Establishing a dynamic model of PWR fuel rod, and relationship between grid stiffness and1st frequency, which helps identify unknown parameter; Introducing a series method of vibration analysis using Strokes’transformation, and giving an explicit expression of the added-mass.