Disposal Critcality Analysis Methodology: BWR Benchmarks

Computer code benchmarks using commercial reactor critical (CRC) data for boiling water reactor (BWR) fuel assemblies using the SCALE and MCNP code packages have been conducted. Depleted fuel inventories which take into account actinide and fission product concentrations are used to develop reactor critical models and the associated neutron multiplication factors. Bias calculated from this integral benchmark method will be applied to the disposal criticality analysis methodology to ensure the sub-criticality of spent commercial nuclear fuel forecast for emplacement into the proposed geologic repository at Yucca Mountain. Previous CRC benchmark calculations have been performed for startup tests for Cycles 13 and 14 of the Quad Cities Unit 2 BWR. Additional benchmarking activities have been performed and applied to evaluations of beginning-of-cycle (BOC) reactor critical models for Cycles 7 and 8 of the LaSalle Unit 1 BWR. Similar to the methodology used for ensuring sub-critical margin for spent nuclear fuel shipping casks, the proposed criticality analysis approach computes the neutron multiplication factor of arbitrary fuel assemblies placed in spent fuel waste packages that represents a bounding criticality model. This is accomplished by calculating spent fuel inventories with the SAS2H sequence of the SCALE code package and computing the neutron multiplication of the spent fuel assemblies in the waste package with MCNP