Abstract: Based on modular ray tracing for rectangle geometry in PWRs, the method of preprocessing for hexagonal geometry was researched, and the geometry information was used as input for the method of characteristics calculation. The code based on this method proved its efficiency as it costed only several milliseconds. In the meantime, the description of hexagonal cell array and assembly was provided, and the representations of different boundary conditions were researched as well. All the results have been applied to code the method of characteristics.