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Nuclear Criticality Calculations for Canister-Based Facilities - Commercial 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 the transportation, aging and disposal (TAD) canister-based systems.
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 handling, transfer and emplacement of TAD canister-based systems in all surface and subsurface facilities, with the exception of the Initial Handling Facility (IHF) and pool operations in the Wet Handling Facility (WHF) (i.e. those operations involving the presence of pool water internal or external to the TAD canister). The criticality safety analysis is provided in Ref. 2.4.1. All off-normal conditions referred to in this document are considered potential end states of category 1 and 2 event sequences.
The criticality safety calculations are performed according to a systematic, methodical process 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 employed for this analysis is described in detail in Section 6.3. 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 TAD canisters);
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 Commercial Spent Nuclear Fuel (CSNF) assembly models, as summarized in Section 1.1.2); 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 the design.

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