The postirradiation annealing response of one SA 302 Grade B plate material and two high-copper weld metals irradiated at 550 °F (288°C) was measured for annealing temperatures in the range 600°F (316°C) to 850 °F (454°C) and annealing times up to 1 week (168 h). Recovery of pre-irradiation microhardness was followed for all three steels. In addition, recovery of ductile-brittle transition temperature (DBTT) was measured for the SA 302 Grade B material. Optical and transmission electron microscopy (TEM) were utilized to characterize the microstructures of the irradiated and annealed SA 302 Grade B plate material. Small fracture specimens of all three steels were broken in an Auger spectrometer. Auger analyses were performed on the fracture surfaces, which were subsequently characterized with scanning electron microscopy (SEM). Microhardness measurements indicated that the weld metal with the highest copper content (0.31 weight percent) and lowest fluence (5.7 × 10¹⁸ neutrons (n)/cm²) was the most resistant to softening under postirradiation annealing. The recovery of ductility as measured by the DBTT shift of the SA 302 Grade B material paralleled the recovery as measured by microhardness. All three steels showed increased recovery with higher annealing temperatures and longer annealing times. No visible microstructural changes accompanied irradiation or annealing. Some evidence for a 5 to 10 percent increase in copper concentration at the fracture surfaces of irradiated specimens was obtained. No significant segregation of any element to the fracture surfaces, however, was observed to result from irradiation or postirradiation annealing. The measured annealing response of these steels agreed well with the values predicted by a previously developed theoretical model based on the dissolution of copper-vacancy aggregates.