AbstractPreliminary models for fuel and cladding performance are described and their predicted behavior compared with experimental data. These models are then applied in a performance analysis of a typical stainless-steel-clad mixed-oxide fuel pin. The results of the analysis indicate that any problems associated with fuel swelling or fuel-cladding interaction for this pin are swamped out by the cladding-swelling effect. The cladding-swelling relationship used requires extrapolation far beyond the fluence range where experimental data are available, thus emphasizing the difficulty encountered in attempting such analyses on LMFBR fuel pins to burnup levels considered economically necessary, but for which materials data are not available.