Failure probability assessment of SNF cladding transverse tearing under a hypothetical transportation accident

This paper presents a structural assessment of spent nuclear fuel (SNF) rod under drop accident of a transport cask using deterministic and probabilistic approaches. The performed case study is a baseline 9-m side-drop scenario during the first 30 years of dry storage. A hypothetical database is generated for five variables related to operating conditions to predict the changes in the mechanical properties of SNF rod using Monte Carlo Simulation and material constitutive models. Finite-element analyses are conducted including a sophisticated transport cask with simplified fuel assemblies to obtain the acceleration response and a detailed full-length single fuel rod to evaluate the deformation response of fuel cladding with various representative material properties. Failure probabilities of a fuel rod subjected to a transverse inertia loading due to side-drop are estimated based on ductile tearing failure criteria. The findings from the dynamic response analysis show that the cladding might yield owing to the 9-m side-drop, but the structural integrity of SNF rod is generally maintained. Yet the probabilistic assessment highlights the importance of conducting further structural integrity evaluation for high burnup fuel under hypothetical accidents as it initially shows concerned failure probabilities comparing to low and intermediate burnup fuel. The modeling technique and analysis methodology outlined in this study have a potential advantage to consider several geometric and material characteristics of SNF rod, hence improving the structural integrity assessment of SNF further.