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Nuclear Criticality Calculations for Canister-Based Facilities - DOE SNF

Bechtel SAIC Company, LLC
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The purpose of this calculation is to perform waste-form specific nuclear criticality safety calculations to aid in establishing criticality safety design criteria, and to identify design and process parameters that are potentially important to the criticality safety of Department of Energy (DOE) standardized Spent Nuclear Fuel (SNF) canisters.
It is intended that the results of the criticality safety calculations provided in this document will be used to support the criticality safety analysis of normal operations and off-normal conditions associated with the receipt, handling and loading of DOE SNF canisters into 5-DHLW/DOE SNF Waste Packages (WPs) in the surface facilities, in addition to the emplacement of loaded and sealed WPs in the sub-surface facility. With respect to surface facilities; it is noted that the Wet Handling Facility (WHF) and Initial Handling Facility (IHF) are specifically excluded from the scope of this calculation. Normally, DOE SNF canisters and WPs will not reside in the WHF and IHF.
The criticality safety calculations are performed according to a systematic analytical method (Section 6.2) to ensure that the configurations analyzed clearly bound those representative of normal conditions, and to provide assurance that sufficient information is available to establish trends and to determine control parameters and their limits for off-normal conditions. The calculation methodology (Section 6.2) employed for this analysis is completely independent of event sequence analyses, although the off-normal conditions examined may represent or bound potential end-states of category 1 and 2 event sequences. The main elements of the calculation method include:
1. Simplification, to reduce or eliminate reliance on design features (e.g. modeling an extensive range of close-fitting full thickness (i.e. 30 cm) reflectors to account for non- fissile materials situated outside the environs of the DOE SNF canisters and WPs);
2. Conservatism, to reduce or eliminate reliance on design parameters or variation in design parameter values (e.g. a variety of conservative modeling treatments are applied to the DOE SNF canister models); and
3. Comprehensiveness, to assure that an in-depth analysis is performed to completely characterize and establish the relative importance of the key aspects of each DOE SNF canister design.

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