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Abstract. In Korea, the storage capability for Spent Nuclear Fuel(SNF)

Spacer grid springs support fuel rods so that the rods keep the position laterally and axially in pressurized water reactor fuel assemblies. The spring load-deflection characteristic, i.e. spring force and stiffness, is needed to evaluate the rod support conditions in the case of fuel assembly manufacturing, shipping and handling. In general, the load-deflection characteristic of grid spring is obtained by mechanical test, but it takes long time to get the new designed grid specimen because the grid manufacturing process comprises strip material manufacturing, stamping die and punch preparation, heat treatment and welding, etc. Therefore the analytic method such as finite element method (FEM) is tried to predict the nonlinear load-deflection characteristic of new designed grid. The spring characteristic mechanical test is simulated with unit cell model and analyzed by FEM tool. Comparing the results between test and analysis shows that more details are needed in the modeling because the boundary conditions of the spring are very complicated and the spring material thickness is changed by the stamping process. The analysis of modified model including expanded cells and thickness changed springs is performed. Using the analytic method of the work to obtain the load-deflection characteristic of spacer grid spring is expected to be useful in the prediction of the characteristic of new designed grids.

The purpose of this study is to develop a finite element model that accurately describes the buckling behavior of a spacer grid. The spacer grid is the most important component of a nuclear fuel assembly and supports the fuel rod with a structurally sufficient buckling strength. Therefore, the development of a reliable spacer grid model is essential to evaluate the mechanical integrity of a nuclear fuel assembly. To achieve this objective, a three-dimensional finite element model was proposed to simulate the buckling characteristics and mechanical behavior of a PWR spacer grid. To simulate the exact mechanical properties of the spacer grid cell, the parameter values required for the model were determined by conducting a fuel rod drag test and spacer grid spring/dimple stiffness test. Finally, a spacer grid static compression test and dynamic impact test were performed according to the gap size of the spacer grid cell, and the model was verified by comparing the test and analysis results. The results obtained using the developed spacer grid finite element model agreed well with the mechanical test results, and it was confirmed that both the buckling characteristics and mechanical behaviors of the model were accurately simulated by the proposed model.