Modeling Used Fuel Response to 30 cm Package Drops

The US Department of Energy Used Fuel Disposition program is performing research to determine the loading conditions that used nuclear fuel (UNF) experiences during normal conditions of transportation (NCT). Materials research is being done to study the mechanical behavior of used fuel, with a particular interest in the high burnup state, when the fuel cladding is expected to have degraded material properties. This study uses numerical models to estimate the mechanical response and the peak strain that occurs in used nuclear fuel cladding during a postulated 30 cm package free drop event to help inform test programs of the anticipated range of response of used fuel. The 30 cm drop scenario represents a normal condition of transportation free drop test specified by 10 CFR 71.71 for the packages modeled in this study. The LS-DYNA explicit finite element analysis code is used to model used nuclear fuel packages impacting an unyielding surface. A detailed 17x17 pressurized water reactor (PWR) fuel assembly is modeled within a generic rail package and a generic truck package. The primary fuel assembly model is represented in enough detail to study the fuel assembly dynamic response and extract local cladding strains. This paper studies the dynamic response of used fuel, estimates the peak cladding strain, and evaluates sensitivities of some of the parameters that influence the cladding strain response, such as temperature, burnup, and variations in fuel rod flexural rigidity due to bonding between the fuel and cladding.