Recommendations for Addressing Axial Burnup in PWR Burnup Credit Analyses

This report presents studies performed to support the development of a technically justifiable approach for
addressing the axial-burnup distribution in pressurized-water reactor (PWR) burnup-credit criticality
safety analyses. The effect of the axial-burnup distribution on reactivity and proposed approaches for
addressing the axial-burnup distribution are briefly reviewed. A publicly available database of profiles is
examined in detail to identify profiles that maximize the neutron multiplication factor, keff, assess its
adequacy for PWR burnup credit analyses, and investigate the existence of trends with fuel type and/or
reactor operations. A statistical evaluation of the keff values associated with the profiles in the axialburnup-
profile database was performed, and the most reactive (bounding) profiles were identified as
statistical outliers. The impact of these bounding profiles on keff is quantified for a high-density burnup
credit cask. Analyses are also presented to quantify the potential reactivity consequence of loading
assemblies with axial-burnup profiles that are not bounded by the database. The report concludes with a
discussion on the issues for consideration and recommendations for addressing axial burnup in criticality
safety analyses using burnup credit for dry cask storage and transportation.