Small-angle neutron scattering of low-Cu RPV steels neutron-irradiated at 255°C and post-irradiation annealed at 290°C

Abstract Fast neutron irradiation of low-Cu reactor pressure vessel (RPV) steels gives rise to the formation of solute clusters and a degradation of mechanical properties. A remarkable acceleration of cluster formation was identified in a previous investigation of low-Cu steels irradiated at 255 °C. The thermal stability of the observed features at a typical RPV operation temperature (290 °C) is of particular interest. Small-angle neutron scattering experiments for three low-Cu materials irradiated at 255 °C and exposed to post-irradiation annealing at 290 °C are reported. The results indicate stability of the irradiation-induced features at a temperature of 290 °C for all three materials. In two cases, even an increase in scattering intensity upon post-irradiation annealing has been observed. The effect of the annealing treatment on the nature of clusters is discussed and a model of the cluster–matrix interface is introduced to rationalize the observed increase in scattering intensity. The role of the residual elements is discussed.