[en] Four aspects of the fast reactor operating cycle that have been experimentally investigated in Zebra are described. Sensitive radiochemical techniques for measuring the capture rates in ²⁴¹Am and ²⁴³Am leading to ²⁴²Cm and ²⁴⁴Cm have been applied to samples irradiated in spectra characteristic of PFR and of a commercial-size reactor. The derived cross sections are compared with those predicted using recent evaluations. Gamma activities induced in a range of elements of potential significance to contamination of the primary circuit in core and axial-breeder locations have been determined by standardised liquid-source counting techniques. Samples of fuel-clad and subassembly-wrapper alloys have also been examined. Results are compared with predictions using currently-recommended cross-sections. The energy release by B-particles from fission products of ²³⁵U and ²³⁹Pu following a 10⁵-second irradiation has been measured over a cooling period of 1 year using a catcher-foil technique and a plastic scintillation detector. Comparisons with summation-code predictions are presented. The formation of plutonium in a radial breeder has been simulated by replacing UO₂ plates by PuO₂/UO₂ to give an average level of 2% Pu/U. The influence of this enrichment on the reaction rates of ²³⁵U, and ²³⁸U and ²³⁹Pu was measured by foil activation methods. Comparisons with diffusion and transport-theory calculations are made. (author)