Abstract
This study presents neutron-physical modeling of radionuclide accumulation in a VVER-1000 reactor after the first fuel cycle using the MCNP6 code and the ENDF/B-VII nuclear data libraries. Calculations were performed to determine the generation of major long-lived fission products (⁹⁰Sr, ⁹⁹Tc, ¹³⁷Cs, ¹²⁹I, etc.), actinides (Np, Pu, Am), noble gases (Kr, Xe), as well as aerosol-forming and iodine-containing radionuclides. Special attention is given to the evaluation of residual activity, and the impact of accumulated isotopes on radiation safety. The findings are of practical importance for the development of spent nuclear fuel (SNF) management strategies, storage design, environmental risk assessment, and preparation for nuclear power plant construction in Kazakhstan.