IRRADIATION CREEP-BEHAVIOR OF LOW-ACTIVATION STEELS IN FFTF MOTA/

Irradiation creep behavior of low activation steels, developed as stru ctural materials for fusion reactors, was investigated. The objective of this study is to provide a fundamental understanding of the irradia tion creep mechanism based on microstructural evolution under fast neu tron irradiation. Pressurized tube creep specimens fabricated from tub e segments were irradiated in the Fast Flux Test Facility (FFTF), Mate rials Open Test Assembly (MOTA) during FFTF Cycles 11 and 12. This pap er provides the first creep results obtained after FFTF cycle-11 irrad iation. (2.25-3)Cr-(1-2)W bainitic steels and 12Cr-2W ferritic/martens itic steels showed equivalent or superior creep resistance to a modifi ed 316 stainless steel, known as Japanese Prime Candidate Alloy (JPCA) , under fast neutron irradiation up to 600 degrees C. For the case of ferritic steels, with increasing Cr content, creep strain increased up to 7 Cr and further increments of Cr content to 8, 9 and 12% reduced creep strain. Swelling enhanced creep near peak swelling temperature o f 410 degrees C was observed. Preliminary TEM observation suggests tha t irradiation induced precipitation and void nucleation were enhanced by applied stress near peak swelling temperature.