The neutron flux and fluence determination on Bulgarian WER-440/230 (Units No 1–4 of Kozloduy NPP) Reactor Pressure Vessels is discussed. In these reactors weld 4 of RPV undergoes the most severe irradiation embrittlement. The choice of the neutron transport calculational parameters is substantiated. The inconsistency of 3D neutron flux values obtained by the 3D code TORT and by the synthesis method of DOT 2D results in the point of most severe irradiation embrittlement is within 3% limits range. Radiochemical analysis of the templets sampled out from the Unit No 2 vessel after 16 cycles of exploitation, before and after the annealing, was carried out. The calculated and experimental values of the neutron fluence on the Unit 2 RPV are compared.