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Criticality Evaluation of Intact and Degraded PWR WPs Containing MOX SNF

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The purpose of this calculation is to perform criticality evaluations for mixed oxide spent nuclear fuel (MOX SNF) in 12 and 21 Pressurized Water Reactor (PWR) waste packages (WPs) for both intact and degraded configurations.
The MOX assembly design considered in previous studies on Pu disposition in commercial reactors is based on the Westinghouse (W) 17x17 Vantage 5 assembly (Ref. 7.2). Depletion analyses of four Pu enrichment and burnup (expressed as gigawatt days/metric ton heavy metal; GWd/MTHM) combinations were performed in Reference 7.4. These are:
1) 4.0% initial Pu, 35.5 GWd/MTHM burnup,
2) 4.5% initial Pu, 39.3 GWd/MTHM burnup,
3) 4.5% initial Pu, 46.5 GWd/MTHM burnup,
4) 4.0% initial Pu, 50.1 GWd/MTHM burnup, and
5) 4.0% initial Pu, 56.6 GWd/MTHM burnup.
This calculation will generally consider only the first two, as these represent the expected lowest assembly burnup at discharge. However, the calculations for the 12 PWR WP will also consider the third and fourth burnup/enrichment pairs, as these are more representative of the higher burned fuel for which this package is intended. Reference 7.4 provides isotopic compositions for each fuel in grams per assembly, for decay times from a few days, out to 1 million years.

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