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EBS Model Development and Evaluation Report

Enginerred Barrier Systems (EBS) model evaluation and development is fundamental to the design and analysis of disposal concepts for generic repository systems within the Used Fuel Disposition R&D Campaign. This analysis is key to the advancement of design concept recommendations for the different host media under consideration. The use of high-fidelity modeling tools and methods along with an experimental program provides the much needed framework to analyze, for example, coupled processes of multilayered EBS plus the intricacies of thermal anisotropies in the host rock media and fluid-mineral interactions. Engineering analysis and trade-off studies of disposal concepts requires a comprehensive evaluation of thermal constraints for the analysis of thermal loads (DSEF, Albany), its effect on temperature-driven coupled processes (chemical, mechanical, transport), and optimization of the EBS configuration within the repository layout.  This report centers on progress made on modeling and experimental approaches to analyze physical and chemical interactions affecting clay barrier performance.  Through the  use of atomistic simulations of clay, high temperature diffusion rates were obtained for chemical species and analysis of swelling phenomena that could inform or be integrated with other models.  The EBS processes evaluated in this report include sorption and transport of radionuclides, THMC behavior of clay barriers, atomistic simulations of barrier materials, and clay/metal interactions with fluids at high temperatures. 

Studies included:  EBS optimization analyses; investigation of reactive transport and coupled THM processes; reactive-diffusive transport modeling approaches for radionuclide migration in bentonite; experimental study of U(VI) sorption onto clay and implications to reactive diffusive transport in bentonite; experimental activities on buffer/backfill interactions at elevated pressure and temperature; thermodynamic database development;  thermodynamic modeling (clay hydration, ion exchange, and mineral thermodynamic properties at elevated temperatures);  molecular dynamic study on the swelling properties of montmorillonite and beidellite clays; Disposal Systems Evaluation Framework (DSEF) User Manual development;  Np(V) sorption and diffusion on montmorillonite clay.