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Criticality Safety and Shielding Evaluations of the Codisposal Canister in the Five-Pack DHLW Waste Package

John W. Davis
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The objective of this analysis is to characterize a codisposal canister containing MIT or ORR fuel in the Five-Pack Defense High-Level Waste (5-DHLW) Waste Package (WP) to demonstrate concept viability related to use in the Mined Geologic Disposal System (MGDS) environment for the postclosure time frame. The purpose of this analysis is to investigate the disposal criticality and shielding issues for the DHLW WP and establish DHLW WP and codisposal canister compatibility with the MGDS, and to provide criticality and shielding evaluations for the preliminary DHLW WP design. The criticality analyses performed for the MIT and ORR fuel show that the intact highly enriched MIT fuel can be safely disposed of within a codisposal canister in the DHLW Five-Pack waste package (both pre and postclosure) with stainless steel/boron absorber plates. Similarly, the intact moderately enriched ORR fuel is critically safe within the codisposal canister. the analyses show the need for a corrosion resistant neutron absorber material within the codisposal canister to accomodate the potential increase in reactivity which occurs as the fuel (MIT or ORR) and basket degrade, while remaining within the canister. They also indicate that further analysis of degraded canister configurations which consider the chemistry and physical configuration of the fuel and basket corrosion products will be required during Phase II. Evaluations of the neutronic behavior of the fuel materials outside the codisposal canister, both wthin the waste package and within the repository drifts, will be performed as part of Phase II.

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