Validation of UNF-ST&DARDS As-Loaded Criticality Calculations

The Used Nuclear Fuel - Storage, Transportation & Disposal Analysis Resource and Data System (UNF-ST&DARDS) has been used for the quantification of the criticality safety margin in as-loaded spent nuclear fuel systems. To have confidence that the criticality margins are conservatively estimated, the calculations must be validated against the appropriate data. This paper discusses efforts to validate the criticality analysis methods used within UNF-ST&DARDS, with a focus on the validation of the operating history assumptions, the depletion calculations, and the criticality calculations. Operating history is validated by comparing the results of calculations using the detailed operating histories from a single cask containing 32 assemblies from a single pressurized water reactor to calculations using the conservative operating parameters used in the UNF-ST&DARDS analysis sequence. Validation of the depletion methodology used in UNF-ST&DARDS is being implemented using a Monte Carlo sampling isotopic uncertainty technique that propagates the measured-to-calculated ratio distributions derived from radiochemical assay data into biases and bias uncertainties that are directly applicable to the specific canister. Criticality code validation within UNF-ST&DARDS uses a sensitivity/uncertainty-based validation technique to select critical experiments that are applicable to each canister and industry standard statistical techniques to calculate the bias and bias uncertainty for the computational methods from the selected critical experiments. The methods used and sample results from each of these validation areas are discussed.