PWR Axial Profile Evaluation

This calculation compares results from criticality evaluations for a 21-assembly pressurized water reactor (PWR) waste package based on 12 axial burnup profile representations for commercial spent nuclear fuel (SNF) assemblies. The burnup profiles encompass the axial variations caused by different fuel assembly irradiation histories in a commercial PWR, including end effects, and the concomitant effect on reactivity in the waste package. The bounding axial burnup profiles in Table T of reference 6.3 are used for this analysis. Criticality evaluations are performed using the MCNP computer program (References 6.4 and 6.5). Axial burnup data for the analysis is obtained from reference 6.6. The calculations evaluate five methods for modeling isotopic concentrations representing the bounding axial burnup profiles in a 21-assembly PWR waste package: Axial profiles with best-estimate isotopic concentrations, Axial profiles with principal isotope isotopic concentrations, Axially homogenized best-estimate isotopic concentrations, axially homogenized principal isotopic concentrations, and isotopic concentrations from generic PWR database (Reference 6.8). The waste package model is discussed in Section 5.1 and the MCNP analysis results are discussed in Section 5.2. The MCNP calculation results for k, sigma, AENCF, and %k/k are summarized in Table 2.