Research on Nonlinear Mechanical Properties of Pressurized Water Reactor Fuel Assembly
Due to the clamping connection between fuel rods and spacer grids in a structure of pressurized water reactor fuel assemblies,there may be friction sliding between the fuel rods and the spacer grid ele-ments,as well as the detachment of fuel rods from the dimples when the assembly is deformed laterally.These two nonlinear factors are the main reasons for the"hysteresis"effect and the stiffness softening of a fuel assembly structure under lateral loads.By means of the equivalent of dynamical characteristics of the fuel assembly structure,an equivalent linear dynamical model of the fuel assembly structure is established in this paper,based on which,a simplified nonlinear static model of the assembly structure is developed.The finite element method is used to study the nonlinear static characteristics of the assembly structure with the two nonlinear factors,the results of which show that the axial slip of the fuel rod will cause the dimples to detach at a lower lateral load,and the detachment of the dimples will cause the fuel rod to ex-perience torsional slip earlier under the combined actions of the two nonlinear factors.When subjected to the same lateral load,the nonlinear model with frictional slippage and dimple detachment has the largest midpoint residual displacement and the greatest reduction in bending stiffness,the nonlinear model with frictional slippage comes second,and the nonlinear model with dimple detachment ranks the last.
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