SANS examination of irradiated RPV steel welds during in-situ annealing

An in-situ annealing experiment was performed using SANS measurements to examine the distribution and thermal stability of irradiation-induced solute clusters in RPV steel welds. Samples were sequentially annealed for 30 min at ∼50 °C intervals in the temperature range 295–497 °C. A methodology was developed to correct the observed data to allow for increased thermal diffuse scattering during annealing which enabled analysis of the changes in coherent scattering in isolation. Results for a low-Ni weld irradiated at low temperature showed apparent decreases in the volume fraction of solute clusters during annealing. However the cluster size was unaffected and these results could have arisen from reduced scattering contrast due to compositional changes, rather than cluster dissolution. A similarly irradiated high-Ni weld exhibited cluster coarsening at high annealing temperatures. Samples of both welds irradiated at a higher temperature were relatively unaffected by annealing except at high temperatures where some shrinkage, indicative of cluster dissolution, occurred.