About calculation of axial diffusion coefficient in nuclear reactors cells

In this paper method for calculation of axial diffusion coefficient is developed. Purpose of this development is to analyze the significance of influence of neutron group spectrum of 2-dimensional problem into the value of axial leakage. To reach this purpose a way for calculation of direction probabilities in 2-D geometry has been suggested. Algorithm and code have been created on the base of this way. The code has been verified with the balance equation of the modeling problem. The results obtained show that if the influence of heterogeneous structure of the neutron flux spectrum on the current along Z-axis is taken into account then for VVER-type cell the coefficient of axial diffusion is changed in fast group (∼2%) and in thermal group (∼15% This discrepancy can lead to the multiplication factor discrepancy about 200-300 pcm. This difference can influence on the neutron leakage in the area closed to reactor reflector. Code VEPS-A can be recommended to estimate the fine effects of axial diffusion coefficients calculations in reactor cell. (authors)