Limited Burnup Credit in Criticality Safety Analysis: A Comparison of ISG-8 and Current International Practice

This report has been prepared to qualitatively assess the amount of burnup credit (reactivity margin) provided by ISG-8 compared to that provided by the burnup credit methodology developed and currently applied in France. For the purposes of this study, the methods proposed in the DOE Topical Report have been applied to the ISG-8 framework since this methodology (or one similar to it) is likely to form the basis of initial cask licensing applications employing limited burnup credit in the United States. This study limits the scope of the comparison to several of the fundamental burnup credit parameters: the nuclides credited in the analysis, the axial-burnup profile, and the cooling time. An investigation of other parameters, such as horizontal burnup effects and isotopic correction factors to account for biases and uncertainties in calculated actinide compositions, were beyond the scope of this review. This report compares the amount of burnup credit provided by the respective methodologies for typical axial-burnup profiles derived from averaging actual PWR axial-burnup distributions. In addition, a limited assessment of several atypical axial-burnup distributions is also included.