Criticality Evaluation of Degraded Internal Configurations for a 44 BWR Waste Package

The purpose of this calculation is to perform an example criticality evaluation for degraded internal configurations of a boiling water reactor (BWR) waste package (WP) containing 44 spent nuclear fuel (SNF) assemblies. The BWR assembly design considered is based on the General Electric (GE) 8x8 assembly (see section 5.1). Depletion analyses for various assembly average enrichment and burnup (expressed as gigawatt days/metric ton Uranium; GWd/MTU) combinations are performed using the SAS2H/ORIGEN-S sequence of SCALE 4.3 (CSCI:30011-2002; Ref. 7.5). For each burnup/enrichment combination, 10 axial fuel nodes are utilized to allow the effects of differences in burnup along the assembly length to be considered. Degraded configuration k-effective values are calculated using MCNP4B2 (MCNP4B2; CSCI: 30033-2003 V4B2LV; Ref.7.6). Calculations are performed for various decay times, burnups, initial enrichments, and configurations. A regression fit of k-effective as a function of burnup and enrichment is generated for the purpose of estimating the amount of the BWR waste stream which could exceed a given k-effective in a given configuration.