Development of Bounding Burnup Axial Profiles for WWER-440 Spent Fuel Pool Burnup Credit Analysis

Bounding axial profiles for WWER-440 spent fuel pool burnup credit analysis were developed. A database of axial burnup profiles of WWER-440 type fuel assemblies and fuel followers was developed and studied to determine the burnup axial profile that results in the maximal neutron multiplication factor. Bounding axial profiles were determined based on the statistical analysis of k_eff of the analyzed profiles from the statistical outliers of the axial profile database. The influence of the identified bounding profiles on k_eff is quantified for the WWER-440 spent fuel pool. Criticality calculations using the database axial profiles were conducted by the MCNP6.1 program. The isotopic compositions of the spent WWER-440 fuels were quantified by the ORIGEN program of the SCALE 6.1 package.