An evaluation is made of variations in reactor physics and engineering parameters during the core lifetime (100 000 MWd/mt) for a large 1000-MW(e) fast-thermal coupled reactor containing oxide fuel material. The analysis includes a comparison between the thorium and plutonium breeding cycles, as well as an estimate of the effects of several types of fuel management on reactor design variables. While the analysis indicates poor breeding characteristics for the particular design considered, the calculational methods developed and the relative parametric trends computed are of more general applicability.