We have studied the annealing response of an irradiated pressure vessel steel, ASTM A302B, using small-angle neutron scattering. We have used two sets of specimens in this study, one irradiated to a fluence of 3 to 4 × 10¹⁹ n/cm² at 288°C, and the other a parallel set of the same steel in the unirradiated condition. We have annealed specimens from each set isothermally at 300, 350, 400, and 450°C for increasing periods of time up to five h, and have observed the variations in the SANS spectra in both irradiated and unirradiated specimens. Changes in the small-angle neutron scattering (SANS) spectra commence at 300°C for the unirradiated material and at 400°C in the irradiated material. The observed response suggests that the changes are caused basically by the precipitation of copper out of solid solution in α-iron during the annealing of unirradiated and irradiated specimens; in the case of the irradiated specimens, the release of damage-induced defects enhances the precipitation of the copper.