Evaluation of spectral history effects in B ampersand W PWRs using Studsvik CMS

Spectral history effects (the effect of spectral hardening or softening on 235U depletion and transuranic isotope buildup) have long been recognized as important considerations in correctly modeling the neutronic behavior of pressurized water reactors (PWRs). However, only with the recent generation of reactor physics modeling capabilities has it been possible to accurately quantify the impact of spectral history effects. In this effort, the Studsvik Core Management System of codes (CASMO-3/SIMULATE-3) has been used to evaluate spectral history effects for two different Babcock ampersand Wilcox PWRs. SIMULATE-3 is an advanced nodal core simulator, which employs a macroscopic cross-section model using two-group cross-section data from the CASMO-3 two-dimensional transport theory fuel assembly depletion code. SIMULATE-3 is unique because it employs weighing factors to provide more weight to recent depletion conditions than to older histories