Publications

Evaluation of Used Fuel Disposition in Clay-Bearing Rock

Jove Colon, Carlos F.; Weck, Philippe F.; Sassani, David C. ; Zheng, L.Z.; Rutqvist, J.R.; Steefel, C.I.; Kunhwi, K.K.; Nakagawa, S.N.; Houseworth, J.H.; Birkholzer, J.B.; Caporuscio, F.A.; Cheshire, M.C.; Rearick, M.R.; McCarney, M.K.; Zavarin, M.Z.; Benedicto, A.B.; Kersting, A.B.; Sutton, M.S.; Jerden, J.J.; Frey, K.E.; Copple, J.M.; Ebert, W.E.

Radioactive waste disposal in shale/argillite rock formations has been widely considered given its desirable isolation properties (low permeability), geochemically reduced conditions, anomalous groundwater pressures, and widespread geologic occurrence. Clay/shale rock formations are characterized by their high content of clay minerals such as smectites and illites where diffusive transport and chemisorption phenomena predominate. These, in addition to low permeability, are key attributes of shale to impede radionuclide mobility. Shale host-media has been comprehensively studied in international nuclear waste repository programs as part of underground research laboratories (URLs) programs in Switzerland, France, Belgium, and Japan. These investigations, in some cases a decade or more long, have produced a large but fundamental body of information spanning from site characterization data (geological, hydrogeological, geochemical, geomechanical) to controlled experiments on the engineered barrier system (EBS) (barrier clay and seals materials). Evaluation of nuclear waste disposal in shale formations in the USA was conducted in the late 70’s and mid 80’s. Most of these studies evaluated the potential for shale to host a nuclear waste repository but not at the programmatic level of URLs in international repository programs. This report covers various R&D work and capabilities relevant to disposal of heat-generating nuclear waste in shale/argillite media. Integration and cross-fertilization of these capabilities will be utilized in the development and implementation of the shale/argillite reference case planned for FY15. Disposal R&D activities under the UFDC in the past few years have produced state-of-the-art modeling capabilities for coupled Thermal-Hydrological-Mechanical-Chemical (THMC), used fuel degradation (source term), and thermodynamic modeling and database development to evaluate generic disposal concepts. The THMC models have been developed for shale repository leveraging in large part on the information garnered in URLs and laboratory data to test and demonstrate model prediction capability and to accurately represent behavior of the EBS and the natural (barrier) system (NS). In addition, experimental work to improve our understanding of clay barrier interactions and TM couplings at high temperatures are key to evaluate thermal effects as a result of relatively high heat loads from waste and the extent of sacrificial zones in the EBS. To assess the latter, experiments and modeling approaches have provided important information on the stability and fate of barrier materials under high heat loads. This information is central to the assessment of thermal limits and the implementation of the reference case when constraining EBS properties and the repository layout (e.g., waste package and drift spacing). This report is comprised of various parts, each one describing various R&D activities applicable to shale/argillite media. For example, progress made on modeling and experimental approaches to analyze physical and chemical interactions affecting clay in the EBS, NS, and used nuclear fuel (source term) in support of R&D objectives. It also describes the development of a reference case for shale/argillite media. The accomplishments of these activities are summarized as follows: Development of a reference case for shale/argillite; Investigation of Reactive Transport and Coupled THM Processes in EBS: FY14; Update on Experimental Activities on Buffer/Backfill Interactions at elevated Pressure and Temperature; and Thermodynamic Database Development: Evaluation Strategy, Modeling Tools, First-Principles Modeling of Clay, and Sorption Database Assessment;ANL Mixed Potential Model For Used Fuel Degradation: Application to Argillite and Crystalline Rock Environments.