Development of nuclear fuel assembly finite element model for mechanical integrity evaluation

Abstract

This paper proposes a finite element model that can accurately simulate the mechanical behavior of a fuel assembly (FA). An FA is a structure that can be subjected to vibrations and shocks in various environments such as earthquakes or transportation and handling. A reliable model is essential to predict the precise mechanical response characteristics of an FA and evaluate its integrity. A consistent model that eliminates extreme simplifications and model variations due to environmental conditions is required. To accomplish this objective, a three-dimensional finite element model was initially developed to simulate the static and dynamic mechanical behavior of an FA. The model was created using ABAQUS v6.14 based on a 17 × 17 type FA and consists of top and bottom nozzles, top, bottom, mid, and intermediate flow mixer spacer grids, guiding tubes, and fuel rods. Here, beam and spring elements were used to reduce analysis time and hardware cost. To verify the proposed model, static compression and impact tests of the spacer grids and static axial compression and lateral bending, axial and lateral impacts, and vibration tests of the FA were performed. Then, the analysis and test results were compared. The proposed finite element model of the FA agreed very well with the test results, and we confirmed that both the static and dynamic mechanical characteristics were simulated effectively by the proposed FA model. We expect that the proposed model can be utilized to evaluate the mechanical integrity of FAs under vibration or drop conditions during seismic events, transportation, and handling.