Tensile strength and Charpy-V (Cv) notch ductility changes with 550°F (228°C) irradiation were explored for several low alloy structural steels. The study was addressed to metal fracture resistance at upper shelf temperatures and encompassed A302-B, A533-B, A543-I, 9Ni-4Co-0.20C, 12-6PH, and l2Ni-5Cr-3Mo steel compositions. Material forms included plate, forging, and weld deposit. Specimen irradiations were conducted in the Advanced Test Reactor; neutron fluences ranged from 1 to 7 × 10²⁰ neutrons (n)/cm² > MeV.

Consistent trends in pre- and postirradiation yield strength versus temperature were observed for all materials. Some capability for uniform strain hardening was shown by each material, irrespective of fluence condition. A significant detrimental effect of high copper content (⩾ 0.15 percent copper) on yield strength behavior with neutron exposure was noted for A302-B/A533-B and A543 steels.

The implications to postirradiation fracture resistance of Cv upper shelf values were assessed using Ratio Analysis Diagram (RAD) procedures developed by the Naval Research Laboratory. The RAD assessments of a low copper content A533-B plate and weld deposit indicated that thick sections of either material would exhibit plastic fracture behavior after 2.5 × 1020 n/cm² > 1 MeV at 550°F (288°C). An experimental 12-6PH alloy of higher strength is also shown to have promise for high fluence applications. A predicted trend for Cv upper shelf energy versus yield strength change with increasing fluence was confirmed by the present findings.