[en] Two nominally identical experiments designed to study the effects of nickel level, chromium level and helium generation rate on the microstructural development and tensile properties of Fe--Cr--Ni alloys are currently undergoing examination. One of these, conducted in ORR at higher He/dpa rate and a lower displacement rate compared to the other experiment in EBR-II, shows substantially more strengthening and a different temperature range of swelling. The effect of irradiation temperature, neutron flux and neutron spectra appear to be larger than those of the compositional variations studied. Transmission electron microscopy (TEM) examination is in progress to determine the origin of the observed changes. 11 refs., 8 figs., 5 tabs