Recent trends in nuclear-pressure-vessel steels for light-water reactors have been toward Ni-Cr-Mo steels. The effect of minor elements—for example, copper and phosphorus—also has been investigated. In this study, the role of nickel, chromium, molybdenum, and copper was investigated to understand the irradiation behavior of pressure vessel steel, using internal friction measurement, transmission electron microscopy (TEM), and mechanical testing. The materials used were Fe-1Ni, Fe-0.25Cr, Fe-0.5Mo, and Fe-0.2Cu. They were annealed or quenched and irradiated 1 ∼ 3 × 10¹⁹ nvt(>1MeV) at 60 C (140 F), and postirradiation annealing was performed in the range 150∼450 C (302∼842 F).

The irradiation hardening was closely related to the amount of the solute nitrogen that corresponded to the amount of the complex defects in the aforementioned alloys. The irradiation hardening was primarily correlated with the strength of the interaction between solute nitrogen (or carbon) atoms. Other contributions of copper and molybdenum were considered.