The character and extent of fuel/cladding chemical interaction (FCCI) have been established for mixed uranium-plutonium oxide, (U,Pu)O2, fuels irradiated in Experimental Breeder Reactor-II to peak fuel burnups to 14.5 at.% at beginning-of-life peak cladding temperatures to 730°C. The changes in character and the correlation of depth of FCCI were determined as functions of the initial as-fabricated fuel oxygen-to-metal ratios (O/M), the cladding inner surface temperature, and fuel burnup. The character of the interaction and its evolution with burnup and temperatures were consistent with oxidation of the chromium in the stainless steel cladding under the influence of fission products. A statistically based design wastage correlation was developed for depth of interaction based on the largest set of fuel pin data for FCCI in the U.S. program drawn from well-characterized and carefully controlled tests. The resultant correlation, linear in burnup, O/M, and cladding temperature, includes a factor for the level of confidence to use in application of the equation in design. The correlation accounted for the few instances, i.e., 3%, that were encountered of deep localized cladding interaction. Significant changes were also noted in the interaction in the cladding opposite the top fuel pellet and the first UO2 insulator pellet. Comparisons to the limited Phénix data available showed the correlation adequately accounted for FCCI in large breeder fuel pins.