[en] The results of calculation of nuclear fuel burnup and independent fission product buildup from ²³⁵U, ²³⁸U, ²³⁹Pu and ²⁴¹Pu in the WWER-440 reactor core are presented. For determining the physical performances of the WWER-440 reactor elementary cell the TRIFON code has been used. The geometry of the elementary cell is a three-zone one. In the central zone the uranium oxide UO₂ with 3.6% enrichment by U²³⁵ is located. The next zone is a zirconium fuel can. The peripheral zone is water coolant. For calculating the combined-iterative method taking into account the variations in the effective neutron flux and neutron spectrum effective hardness is employed. Fuel elements situated in the central part of the assembly and those on the periphery are considered. The dependence of variations in concentrations of ²³⁵U, ²³⁶U, ²³⁷U, ²³⁸U, ²³⁷Np, ²³⁹Pu, ²⁴⁰Pu, ²⁴¹Pu, ²⁴²Pu, ²⁴³Am, ²⁴⁴Cm on fuel burnup is obtained. On the basis of the analysis of the results obtained the conclusion is drawn that it is sufficient to perform calculations for ²³⁵U, ²³⁶U, ²³⁸U and ²⁴⁴Cm in single stage approximation. For all isotopes the results monotonously vary with the increase of number of stages