Method for Calculating the Neutron Diffusion Coefficient in a Nuclear Reactor Cell

An approach to solving the three-dimensional transport equation is described. Directional probabilities, which make it possible to analyze axial leakage numerically, are defined. The problems of modeling the boundary conditions for the neutron flux under ordinary operating conditions of reactors and under the conditions of dewatering are discussed. The results obtained show that if the effect of the spectrum of the two-dimensional problem of a VVER cell is taken into account, then the axial leakage changes, especially near the reflector. The axial leakage also increases if the cell contains dewatered channels, but only if the boundary conditions are modeled in the form of mirror reflection on a real hexahedral boundary. This effect vanishes if the equivalent cylindrical cell approximation is used and the boundary conditions are modeled in the form of isotropic reflection.