Modeling and Analysis of Used Nuclear Fuel during Normal Conditions of Rail Transportation

In 2017, the United States Department of Energy collaborated with Spanish and Korean organizations to perform a multimodal transportation test (MMTT) to measure shock and vibration loads imparted to used nuclear fuel (UNF) assemblies. This test used real fuel assembly components containing surrogate fuel mass to approximate the response characteristics of real, irradiated used nuclear fuel. Pacific Northwest National Laboratory (PNNL) was part of the test team and performed modeling and analysis using the test data to validate numerical models and analysis methods to predict the dynamic response of the cask and conveyance system, including the structural-dynamic response of fuel assemblies and fuel cladding. The analysis chain begins with a railcar dynamics model using the NUCARS railcar dynamics software to estimate the dynamic response of the conveyance system to the speed and a specified track geometry. The NUCARS model calculates the response of the conveyance system up to the cask. The cask motion is then used as an input to structural-dynamic models of the fuel assembly or a single fuel rod, using the LS-DYNA explicit finite element code. The key output of the modeling is fuel cladding strain, which is used in stress analysis and fatigue analysis to demonstrate fuel cladding integrity. This work also considers stress concentrations in the cladding due to the interaction of discrete fuel pellets with the cladding tube in bending load cases. This paper describes model development, defines the broader analytical methodology, and provides a validation of the models and the methodology through comparison to the test data collected during the MMTT. The validated models and analysis methodologies described in this paper are being applied in ongoing modeling and analysis work to evaluate other UNF transportation configurations that differ from the MMTT configuration.