Model Analysis of Fuel Assembly Grid Spring Stiffness

Grid spring is a critical component of PWR fuel assembly, which provides clamp function for the fuel rod. Stiffness is a critical characteristic of grid spring, which is related to the in-pile operational performance of the fuel rod. According to the grid spring structure and mechanical characteristics, this paper proposes a mechanical analysis model of the grid spring, and the theoretical stiffness calculation formula is obtained through deduction, and the grid spring theoretical stiffness model is also obtained. Furthermore, the finite element stiffness models of grid spring with various sizes are established in the commercial finite element code ABAQUS, and the deformation and stiffness curves of grid spring are obtained by calculation. By comparison between the FEM analysis results and the theoretical calculation ones, the rationality of the theoretical stiffness model is proved, and then the advantages and shortcomings of the theoretical stiffness model are analyzed. The theoretical stiffness model of grid spring proposed for the first time in this paper can be used to replace the finite element iterative process during the design of grid scheme, and the main design dimensions of the optimized scheme can be obtained quickly. However, the theoretical method in this paper cannot replace the experiments, and tests are still needed to determine the stiffness of the grid spring after the scheme is solidified. The grid spring theoretical model in this paper provides a new idea to quickly optimize the fuel assembly grid spring design.