Two-dimensional baffle/reflector constants for nodal code in PWR core design

Currently nodal codes are widely used in three-dimensional core calculation . For nodal calculations, in addition to fuel assembly homogenization const ants, baffle/reflector homogenization constants (B/R constants) have to be generated. Due to the complexity of its geometrical structure, the baffle/r eflector region is usually represented by the two regions, which are called flat edges' and corner edges. B/R constants are generated using an equival ent one-dimensional model for each region. However, errors of 3-4% appear f or fuel assemblies along core corner when one-dimensional B/R constants are used. Therefore, in order to improve the accuracy of power distribution ca lculation based on the nodal method, B/R constants need to be calculated by modeling the geometrical configuration of the baffle/reflector region in g reater detail. For this purpose, a method of calculating two-dimensional B/ R constants that reflects the geometrical configuration has been developed, in which the geometrical configuration ouside the core is treated explicit ly using a two-group fine-mesh diffusion code. The two-dimensional B/R cons tants thus obtained have reproduced assembly power from heterogeneous calcu lation within 0.5%, error regardless of fuel loading patterns.