Abstract
A series of studies investigating the behavior of critical as-loaded DPCs was conducted. The relationship of neutron multiplication factor as a function moderator density was quantified for various DPC types. During this effort, some unexpected over-moderated behavior was found for certain DPCs related to the method in which UNF-ST&DARDS models DPCs with degraded baskets. This phenomenon was observed for certain BWR DPCs (MPC-89 and MPC-68M) that have neutron absorbers contained in the basket structure itself, which is removed in the criticality model. Another study investigated the effect of removing the assumption of thermal equilibrium between the DPC and the repository, resulting in a time-dependent power curve that approaches the estimated quasi-static power level during the first few centuries of criticality. This effect was shown to have a minor impact on nuclide inventories when considering criticalities on the order of thousands of years. The final investigation covered in this work showed the effect of criticality start time on the duration of the criticality. The results showed a minor effect dependent on the power level, which combined the effects of depletion once criticality started with the increase of keff as a function of decay in the nuclear fuel that peaks around 20,000 years. This investigation also revealed an unexpected phenomenon in which the multiplication factor peaked after thousands of years of criticality. A hypothesis related to a shift in power from the tops to the bottoms of the assemblies within the DPC was presented, along with supporting data. Future work includes expanding the analysis of critical DPCs to include cases in which boiling occurs to limit criticality rather than only cases in which moderator density changes at the repository pressure of 50 bars can maintain a keff around unity. Understanding the behavior of DPCs with this amount of excessive reactivity will further help conceptualize the possible consequences of criticality if DPCs are used for long-term disposal.
| Original language | English |
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| Title of host publication | Proceedings of the International High-Level Radioactive Waste Management Conference, IHLRWM 2022, Embedded with the 2022 ANS Winter Meeting |
| Publisher | American Nuclear Society |
| Pages | 249-254 |
| Number of pages | 6 |
| ISBN (Electronic) | 9780894487897 |
| DOIs | |
| State | Published - 2022 |
| Event | 2022 International High-Level Radioactive Waste Management Conference, IHLRWM 2022, Embedded with the 2022 ANS Winter Meeting - Phoenix, United States Duration: Nov 13 2022 → Nov 17 2022 |
Publication series
| Name | Proceedings of the International High-Level Radioactive Waste Management Conference, IHLRWM 2022, Embedded with the 2022 ANS Winter Meeting |
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Conference
| Conference | 2022 International High-Level Radioactive Waste Management Conference, IHLRWM 2022, Embedded with the 2022 ANS Winter Meeting |
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| Country/Territory | United States |
| City | Phoenix |
| Period | 11/13/22 → 11/17/22 |
Funding
This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).
