A series of three Fe-15Cr-XNi alloys in both annealed and cold worked conditions was irradiated in the fast flux test facility (FFTF) at 495°C to 14 dpa. The experiment was developed to determine the separate and synergistic effects of nickel and phosphorus content, cold work, and helium/dpa ratio. This experiment was conducted without introducing variations in displacement rate, a variable known to strongly influence microstructural evolution. Each alloy condition was irradiated in two variants, one with natural nickel and one enhanced with the 59Ni isotope. The latter variant produces helium/dpa ratios typical of fusion reactor spectra while the former yields a much lower level of helium. The results show that helium alters the microstructural evolution somewhat at 495°C, but its effect is relatively small compared to the influences of the other variables studied. Increases in starting dislocation density, nickel content, or phosphorus level all retard swelling temporarily while higher rates of helium generation usually, but not always, accelerate swelling. Phosphorus addition of 0.04 wt% not only decreased swelling but led to refinement of dislocation loop microstructure and stabilization of dislocation networks created by cold working. Phosphide precipitates did not form at this temperature and dose level.