The continuous slowing down integral transport theory has been extended to perform criticality iteration with fuel-depletion analysis for evaluating exposure-dependent spectral transitions in fast reactor core-blanket systems. The theory was applied to conventional and heterogeneous configurations, obtaining excellent predictions of the eigenvalue and the spectra. The results indicate the importance of space-dependent analysis involving considerable energy detail. The initial value energy considerations of the theory are the principal advantage in data processing and group collapse procedures requiring such detail. Several simplifying features were observed, further enhancing the advantages of the present method. The transport theory sophistication was attained without significant penalty as the spatial probabilities varied weakly with exposure. Similar insensitivity of the slowing down parameters and resonance self-shielding factors provide substantial savings in computer running time. Nonvariation of these parameters had small effects on fuel cycle characteristics. An analytical solution of the depletion equations was obtained based on the observed weak exposure variation of important microscopic reaction rates. The space-dependent slowing down theory as generalized here is thus shown to be an attractive tool for incorporating the required space-energy detail in a comprehensive fast reactor fuel cycle analysis.