Nano-oxide particle stability of 9–12Cr grain morphology modified ODS steels under neutron irradiation

ODS steels based on a 9–12Cr composition were developed with modified grain morphology and incorporation of recrystallization heat treatment and martensitic transformation process into previous tube fabrication methods. The modifications were for improving strength anisotropy in hoop and longitudinal directions of cladding tubes. Specimens were irradiated in the experimental fast reactor JOYO at temperatures of 670–807 K to 15.0 dpa maximum. TEM and/or HRTEM observation indicated that nano-scale sized oxide particles were finely distributed in each alloy and were relatively stable under neutron irradiation. Quantitative constitution analyses showed that most of the oxide particles were comprised of yttrium and titanium, and that they were in most case non-stoichiometric. Comparing with past reports on neutron-irradiated ODS steels, the main factors determining oxide stability under neutron irradiation are shown to be irradiation temperature and/or type of oxide.