Structural integrity of a high-burnup spent fuel rod under drop impact considering pellet-clad interfacial bonding influence

Variation of several uncertain properties of an irradiated fuel assembly would result in changes in the buckling and bending resistance that could lead to fuel rod failure in a drop accident. Dynamic analysis of the fuel rod composite is a very complicated process due to limited knowledge on important parameters relevant to design safety, such as the material properties of the irradiated cladding and the interaction between fuel pellets and cladding. In order to better understand the behavior of a spent nuclear fuel (SNF) rod in a drop impact, a detailed finite-element (FE) model for a single fuel rod was developed considering post-irradiated fuel conditions. Free-drop analyses of two bounding cases were conducted using FE analysis, with ten assumed generalized interface bonding and de-bonding configurations to demonstrate the pellet-clad interfacial bonding influence on fuel rod behavior. It is revealed that the interfacial bonding between pellet and cladding shows a significant influence on the magnitude of the maximum principal plastic strain and its location, and on the overall structural resistance. The key feature of the proposed analysis procedure is seen in its capability to consider a range of parameters that can be included in the FE model, in addition to providing a more realistic and descriptive prediction of fuel rod behavior. The procedure and methodology developed for the numerical simulation in this work can be further extended to support the development of guidelines for safe handling of SNF when augmented by realistic data obtained experimentally.