A modular code WYKAS for burnup calculations of adjacent hexagonal fuel assemblies has been developed. The code allows, for a nonuniform hexagonal mesh, to take into account the real dimensions of the gap between assemblies. The code utilises two types of macroscopic cross section libraries with different levels of sophistication.
The effective calculations have been carried out for typical conditions occuring in a VVER-440 reactor core. Two sets of comparisons are presented: results based on different libraries and results obtained with and without homogenization of macroscopic cross sections throughout the hexagonal fuel assembly with its central channel and gap between assemblies. The results are presented in the form illustrating the influence of neighbourhood on flux and power distributions in a fuel assembly.