Modified One-Group Diffusion Scheme for Calculating Gross Power Distribution in a BWR Core

Abstract

A new modified one-group diffusion scheme for one- and two-dimensional calculations ofthe gross power distribution in the BWR core is presented. The particularity of the presentmethod is that the fine distribution of the ratio between thermal and fast neutron fluxeswithin each fuel assembly is estimated analytically. Since this estimation can be performedlocally and without requiring knowledge of the fast neutron distribution, the method is quiteeffective in reducing computing time. Procedures for special treatment at the two-dimensionalcore-reflector boundaries are also derived from analytical considerations. The results obtainedfrom a series of test calculations indicate that the present method assures an accuracy almostequal to the conventional two-group calculation, and without requiring much more computingtime than the conventional one-group calculation.
The applicability of the method to three-dimensional calculations is also discussed.