David Andersson1,Christopher Matthews1,Romain Perriot1,Michael Cooper1,Benjamin Liu1,Christopher Stanek1
Los Alamos National Laboratory1
David Andersson1,Christopher Matthews1,Romain Perriot1,Michael Cooper1,Benjamin Liu1,Christopher Stanek1
Los Alamos National Laboratory1
Point defect evolution under irradiation influences important nuclear fuel performance characteristics such as fission gas evolution and dislocation growth. The Centipede cluster dynamics code, based on the MOOSE framework, was developed to simulate these processes, specifically targeting the known sensitivity to oxygen non-stoichiometry and complex defect clusters in UO<sub>2</sub> based fuels. In this presentation the Centipede capabilities will be reviewed and then exemplified for standard UO<sub>2</sub> and doped UO<sub>2</sub> nuclear fuel as well as for UCO fuel kernels used in TRISO fuel particles. The cluster dynamics model requires a large set of parameters as input, which are derived from atomic scale simulations. The Density Functional Theory (DFT) and empirical potential calculations used for this purpose are illustrated. The UO<sub>2</sub> case establishes a baseline capability, which is then expanded to Cr-doped UO<sub>2</sub> by modifying the prevailing oxygen chemical potential of the fuel. Simulations of uranium self-diffusion and Xe diffusion are demonstrated for both fuel types and compared to available experiments. The results are analyzed in terms of parameter uncertainty and the need for limited parameter calibration will discussed. UCO fuel kernels are used in TRISO particles and consist of a uranium dioxide (UO<sub>2</sub>) and uranium carbide (UC<sub>2</sub>) mixture. UC<sub>2</sub> is added to suppress the formation of carbon monoxide gas, however it also alters the chemistry (non-stoichiometry) of the UO<sub>2</sub> matrix by imposing reducing conditions, which is known to influence diffusion parameters governing gas and fission product release. The properties of UCO fuel kernels are captured in the Centipede code by changing the chemical potential according to the presence of UC<sub>2</sub>, while also updating the database to include Xe diffusion mechanisms relevant for reducing conditions. In addition, Ag diffusion is investigated using the same Centipede framework. The predicted fission gas and Ag diffusivities in UCO are compared to the UO<sub>2</sub> benchmark case. Finally, application of fission gas diffusion models in engineering scale fuel performance analysis is discussed.