VVER-1000 reactors use cylindrical smooth-core fuel rods. Previously, a model to determe the fuel rod temperature field in a two-dimensional problem statement has been developed and verified. However, modelling assumptions do not consider the influence of variable thermophysical properties, radiation heat transfer, and the opening in the fuel rod on the final parameters of the temperature fields. The impact assessment is an urgent task to improve the economic efficiency of the fuel cycle and the capacity of power units. To develop models and study the features of energy release in nuclear reactors, a numerical package of thermophysical modeling COMSOL Multiphysics software is used. The simulation of temperature fields is performed based on the heat equation with an internal heat source, under the boundary conditions of the second kind at the ends of the fuel rod and the boundary conditions of the third kind on the side surface of the rod. Аn axisymmetric model in two-dimensional problem statement and a three-dimensional model of the fuel rod are developed. The temperature distribution fields are determined by the finite element method. The results of calculations of various design fuel rods are presented. The results have showen that the radiation heat transfer significantly affects the maximum fuel temperature (UO2). The impact degree of variability of thermophysical properties and radiation heat transfer is determined. It was found that the temperature characteristics under different specified conditions have a difference in the range of 15,5–282,0 K (0,8–14,4 %). The developed models are reliable and confirmed by the previously verified model, the characteristics of the fuel assembly used on the VVER-1000 units. The results presented can be used for mathematical modeling of heat transfer processes, both during the modernization of the equipment in operation, and during the development, design, and operation, which will increase the efficiency of electric energy generation at the power unit of a nuclear power plant.