The development of irradiation-induced precipitates in VVER-440 type reactor pressure vessel steels 15Kh2MFA and weld metals SV-10KhMFT during irradiation and post-irradiation annealing is studied by small angle neutron and X-ray scattering. The kinetic conditions for the precipitation of particles, which already exist in the unirradiated state, seem to be improved at temperatures of about 270°C due to the irradiation. The size distribution of the irradiation-induced precipitates depends on the copper content and differs between weld and base metal. A strong correlation between the formation of irradiation-induced precipitates and the irradiation hardening is found. The hardness nearly linearly depends on the number of these precipitates.