During the late 1960s, the irradiation effects discoveries of void swelling, irradiation creep and loss of ductility of stainless steels created significant impacts on the design and development of fast breeder reactors. The Fast Flux Test Reactor (FFTF) was the first fast reactor to be designed subsequent to the initial quantification of these irradiation effects. This paper describes the experience of incorporating irradiation effects data in the design of the FFTF core restraint system and the evolutionary paths followed to develop the advanced materials in current use and under development.