Evaluation of Burnup Credit for Accommodating PWR Spent Nuclear Fuel in High-capacity Cask Designs

This paper presents an evaluation of the amount of burnup credit needed for high-density casks to
transport the current U.S. inventory of commercial spent nuclear fuel (SNF) assemblies. A prototypic
32-assembly cask and the current regulatory guidance were used as bases for this evaluation.
By comparing actual pressurized-water-reactor (PWR) discharge data (i.e., fuel burnup and initial
enrichment specifications for fuel assemblies discharged from U.S. PWRs) with actinide-only-based
loading curves, this evaluation finds that additional negative reactivity (through either increased credit for
fuel burnup or cask design/utilization modifications) is necessary to accommodate the majority of SNF
assemblies in high-capacity storage and transportation casks. The impact of varying selected
calculational assumptions is also investigated, and considerable improvement in effectiveness is shown
with the inclusion of the principal fission products (FPs) and minor actinides and the use of a bounding
best-estimate approach for isotopic validation. Given sufficient data for validation, the most significant
component that would improve accuracy, and subsequently enhance the utilization of burnup credit, is the
inclusion of FPs.