E ects of Control Blade History, Axial Coolant Density Profiles, and Axial Burnup Profiles on BWR Burnup Credit

A technical basis for peak reactivity boiling water reactor (BWR) burnup credit (BUC) methods was recently generated, and the technical basis for extended BWR BUC beyond peak reactivity is now being developed. In this paper, a number of e ects related to extended BWR BUC are analyzed, including three major operational e ects in BWRs: the coolant density axial distribution, the use of control blades during operation, and the axial burnup profile. Specifically, uniform axial coolant density profiles are analyzed and compared to results for realistic coolant density profiles taken from operating data. A new temporal fidelity study was performed for the coolant density profile change as a function of operating time by consecutively simulating the coolant density profiles first– , second–, and third–cycle fuel assemblies. Realistic control blade histories and their impact on cask reactivity are also analyzed. Preliminary analysis of the axial burnup profile is also provided.