Positron lifetime and annihilation gamma-line Doppler broadening measurements were used to study the irradiation response and postirradiation annealing behavior of pressure vessel model steels and ternary iron alloys. The steel samples had the basic composition of A533-B and A302-B type steels with varying key impurity elements, i.e., Cu, P, and Ni. The steels and the ternary iron alloys were neutron irradiated at 288°C into a fluence of 2.5 and 4.6 ˟ 1023 neutrons/m-2, E > 1 MeV, respectively.
Due to irradiation, microvoids were formed in the ternary iron alloys but not in the steel samples. The irradiation response measured as the vacancy-type defect content of the specimens was found to be dependent on chemical composition. The vacancy defects annealed out in all the specimens in the temperature range of 400 to 500°C. In the annealing behavior, there were some smaller differences in details.