Structural Stability Evaluation of Independent Spent Fuel Storage Casks

Most nuclear power plants in the US store the spent fuels in independent spent fuel storage casks and these casks are typically placed on concrete pads outside of the fuel handling building. Under plant design basis events, the spent fuel storage casks should maintain stability without tip-over or direct contact with each other. Sliding and rocking of the casks can be determined using nonlinear dynamic analyses under artificial acceleration input motions. Alternatively, approximate equations developed for sliding and rocking of rigid bodies are used as shown in ASCE 4-16. However, these equations consider rocking and sliding as two separate events. Due to the shortcoming of the approximate method, many power plant owners are required to perform extensive nonlinear analyses to ensure cask stability during seismic events. In this study, an independent spent fuel storage cask model is developed and nonlinear dynamic analyses are conducted with seismic input motions that meet the current US Nuclear Regulatory Commission requirements. The analysis results are compared with the approximate method in ASCE 4-16. Based on the comparison, recommendations are made for the use of the approximate approach.