Reactor pressure vessel steels of the Soviet-type 15Kh2MFA (Cr-Mo-V steels) are used in the VVER-440 type reactors, whereas steels of the Soviet type 15Kh2NMFA (Ni-Cr-Mo-V steels) are used in the WER-1000 type reactors. Eleven different materials, i.e. seven base metals and two weld metals of the type 15Kh2MFA, as well as one base metal and one weld metal of the type 15Kh2NMFA were available for the investigations. The small angle neutron scattering technique using the SANS-2 facility at the FRG-1 reactor in Geesthacht was employed to study the radiation-induced defect microstructure in the as-irradiated materials. The results are discussed in terms of the influence of different impurity contents and irradiation conditions on the defect microstructure.