Criticality Analysis for Direct Disposal of Dual-Purpose Canisters

摘要

This paper discusses using an as-loaded modeling of DPCs to perform criticality analysis supporting their direct disposal. Using data from 616 analyzed DPCs, it is demonstrated that the as-loaded criticality analysis approach is sufficient to show subcriticality over a repository time frame for nearly all BWR canisters and nearly all PWR flux trap canisters under the degraded absorber scenario. Approximately 1/3 of PWR developed-cell canisters can be shown to be subcritical under the current modeling assumptions for the degraded absorber scenario. It is possible that application of improved damaged fuel treatment distributions and more representative axial burnup distributions can improve that fraction. The degraded basket condition results in higher k_(eff) values, but direct disposal of DPCs may be possible through crediting chlorine in groundwater, using analytical techniques such as consequence analysis, or implementing physical processes such as canister filling.