The objective of EBS Disposal R&D is to address the technical elements necessary to evaluate EBS design concepts specific to the select host media. Emphasis includes analysis and study of thermal, mechanical, and chemical processes that influence the performance of EBS and developing modeling capability for reliable assessment of these processes and ultimately supporting the Generic Disposal System Analysis (GDSA) model with detailed coupled THMC process models. Researches in EBS Disposal R&D cover a wide range of modeling and experimental work, including the fundamental understanding of the chemical controls on montmorillonite structure and swelling pressure using microscope modeling and imaging, studying the sorption of radionuclide using sophisticated MD models and column tests, advanced modeling and experiment for the diffusion of radionuclide through EBS, and large scale couple THMC models for the generic repository and in situ tests via international collaboration. Specifically, we have the following research activities:
THMC modeling of the generic repository under high temperature conditions
Research highlight: While thermal limit of 100 ⁰C at the interface of canister/bentonite buffer was widely adapted in most concepts of repository design, allowing higher thermal limit can significantly reduce the cost of repository. Moreover, disposal of Dual Purpose Canister can lead to temperature in bentonite much higher than 100 ⁰C. We therefore developed coupled THMC models with temperature of 200 ⁰C to evaluate the long term geochemical alteration of bentonite and its effect on the swelling stress of benonite. Meanwhile, we are developing advance simulator than can model coupled THMC processes simultaneously.
Zheng, L.; Rutqvist, J.; Birkholzer, J. T.; Liu, H.-H., On the impact of temperatures up to 200 °C in clay repositories with bentonite engineer barrier systems: A study with coupled thermal, hydrological, chemical, and mechanical modeling. Engineering Geology 2015, 197, 278-295. https://doi.org/10.1016/j.enggeo.2015.08.026
Zheng, L.; Rutqvist, J.; Xu, H.; Birkholzer, J. T., Coupled THMC models for bentonite in an argillite repository for nuclear waste: Illitization and its effect on swelling stress under high temperature. Engineering Geology 2017, 230, 118-129. https://doi.org/10.1016/j.enggeo.2017.10.002
Contact: LianGe Zheng
Chemical controls on montmorillonite structure and swelling pressure
Research highlight: Despite many decades of study, quantitatively predictive models for diffusion-driven mass transport through clay rich (geo)materials remain elusive. Predicting mass transport through clays is difficult, because the material is largely nanoporous, and interactions between charged clay layers and nanopore fluid give rise to structural and dynamical fluid properties that cannot be quantified with continuum models. We have combined in situ small-, mid- and wide-angle X-Ray scattering experiments with swelling pressure measurements for the swelling clay Wyoming montmorillonite, a key constituent of bentonite barriers. Our aim is to understand the influence of pore fluid chemistry on the microstructure of clay under varying stress states relevant to engineered barrier systems. Complementary molecular simulations are shedding light on the physiochemical properties of the clay nanoporous interlayer region that dictate the thermodynamics of clay swelling.
Subramanian, N., Whittaker, M.L., Ophus, C. and Lammers, L.N. (2020) Structural Implications of Interfacial Hydrogen Bonding in Hydrated Wyoming-Montmorillonite Clay. The Journal of Physical Chemistry C.
Whittaker, M.L., Lammers, L.N., Carrero, S., Gilbert, B. and Banfield, J.F. (2019) Ion exchange selectivity in clay is controlled by nanoscale chemical–mechanical coupling. Proceedings of the National Academy of Sciences 116, 22052-22057.
Contact: Laura Lammers
Experimental investigations on bentonite and other clay-based samples
Research highlight: Bentonite is one of the primary materials under investigation for use as an engineered barrier during geologic storage of nuclear waste due to its high swelling capacity and low hydraulic conductivity, which restricts contaminant mobility to slow diffusion-based transport, and its high capacity for sorption of radionuclide contaminants, which slows transport even further. The combination of groundwater intrusion from surrounding host-rock and high temperatures (100-200 °C) near the waste canisters can lead to temporally and spatially variable profiles in water saturation, pore water chemical composition, and temperature, which may in turn affect radionuclide transport. In this work we use a combination of batch experiments, diffusion experiments, and modeling to investigate the effects of (1) long-term bentonite heating, (2) porewater composition/bentonite swelling, and (3) radionuclide aqueous speciation and adsorption, on radionuclide transport. We focus on two important radionuclides, uranium (U-238, U-235), which is a major component of spent fuel, and selenium (Se-79), which is a major driver of the safety case for nuclear waste disposal due to its low adsorption to bentonite.
Fox, P. M., Tinnacher, R.M., Cheshire, M.C., Caporuscio, F., Carrero, S., and Nico, P.S. (2019). Effects of bentonite heating on U(VI) adsorption. Applied Geochemistry 109: 104392.
Tournassat, C., Tinnacher, R.M., Grangeon, S., and Davis, J.A. (2018). Modeling uranium(VI) adsorption onto montmorillonite under varying carbonate concentrations: A surface complexation model accounting for the spillover effect on surface potential. Geochimica et Cosmochimica Acta 220: 291-308.
Contact: Patricia Fox
THMC modeling of large scale in situ tests: FEBEX-DP and HotBENT
Research highlight: One of the challenges of developing THMC model and predicting the long-term alteration of bentonite is model validation. Data collected from large scale in situ tests provide a unique opportunity to validate the THMC model and deepen the understanding of coupled THMC process at the scale of a repository. In FEBEX dismantle project (FEBEX-DP), an in situ test for EBS bentonite in granite tunnel at Grimsel, Switzerland was dismantled after 18-years of heating at 100 ⁰C and hydration. THMC model was developed for the test and provided a reasonable interpretation of all THMC data, which laid the foundation for conceptualizing the THMC process for bentonite barriers in the nuclear waste repository. While THMC modeling for bentonite under 200 ⁰C for the generic repository was conducted to obtain a preliminary understanding of the evolution of bentonite if heat release is much higher than the small canister, model results have to ultimately be tested by field test. A large scale in situ test of bentonite with heating up to 200 ⁰C is under construction in the Griseml test site. The project was led by NAGRA and DOE is one of the major partners. LBNL has been supported the project via modeling and will continue to model the test during the operation time.
Zheng, L.; Xu, H.; Rutqvist, J.; Reagan, M.; Birkholzer, J.; Villar, M. V.; Fernández, A. M., The hydration of bentonite buffer material revealed by modeling analysis of a long-term in situ test. Applied Clay Science 2019, 105360. https://doi.org/10.1016/j.clay.2019.105360
Contact: LianGe Zheng
Heating and hydration column test on bentonite
Research highlight: The barrier system surrounding the waste containers is a key engineering component to provide sealing for nuclear waste storage. Bentonite clay based engineered barrier system (EBS) is proposed as a potential solution for the repository design for spent nuclear fuel and waste because of its low permeability, large swelling capacity and retention property, as well as thermal stability among other desired characteristics. To complement the field scale HotBENT experiment, LBNL is conducting a benchtop-scale laboratory experiment to understand the impacts of heating and hydration on bentonite at high temperature, and to generate complementary datasets for comparison with the HotBENT experiment at the Grimsel sites and benchmarking of predictive models.
Our experiments are designed to simulate realistic heating and hydration conditions at the field scale to the extent possible. Innovative design features and setup procures are implemented together with a comprehensive set of characterization and imaging technologies. This is a unique and first of its kind design and experiment and we hope this will lead to a new capability for better understanding the behavior of clay systems under a wide range of heating and hydration conditions.
Selected publications: N/A
Contact: Sharon Borglin
Coupled microbial-abiotic processes in EBS and host rock materials
Research highlight: Experiments are being conducted to see if EBS materials from the FEBEX field heater test, recovered in 2015, possess microbial communities capable of metabolizing H2 and how the FEBEX treatment impacted that capabilities. Preliminary results indicate that EBS materials maintain microbial communities with the potential to metabolize H2, and these communities were enriched upon incubation with H2. However, it is interesting that the material from the hot zone did not show that potential. Whether that is due to the heating or the drying or both is unknown at this point. While these results are extremely preliminary at this point they do point strongly to the conclusion that the microbial metabolic potential of EBS materials should be considered in assessing and predicting their behavior in terms of chemical transformations. Longer term efforts will include the examination of other potential metabolisms, e.g. sulfate or Fe transformation, and how pressure impacts the function of the microbial communities.
Jonny Rutqvist, Yves Guglielmi, Hao Xu, Yuan Tian, Piotr Zarzycki, Hang Deng, Pei Li, Mengsu Hu, Peter Nico, Sharon Borglin, Patricia Fox, Tsubasa Sasaki, Jens Birkholzer. 2020, Investigation of Coupled Processes in Argillite Rock: FY20 Progress. LBNL-2001324
Contact: Peter Nico
Computational prediction of the retention of multi-nuclear radionuclide complexes by bentonites
Research highlight: The capability of a bentonite barrier to impede the transport of long-lived radionuclides is an important aspect of the performance evaluation of any storage strategy. A scenario for radionuclide release involves groundwater reaching a corroded canister and mobilizing radionuclides, such as 233U, 237Np, and 239Pu. Thus, knowledge of the aqueous speciation and chemistry of these radionuclides under relevant conditions, their interactions with clay minerals and their mobility within bentonite matrix is critically important for evaluating repository performance. The ultimate goal of this work is to develop the predictive computational model of radionuclide retention in bentonites – relevant for nuclear waste disposal safety assessments. In particular, we proposed to use molecular modeling to parametrize meso- and macroscopic models of radionuclide migration in the clay-barriers, and clay-rich rocks and soils in order to develop a robust field-scale safety assessment model. The molecular modeling offers an alternative route for model parametrization, which does not involve experimental measurement of the toxic radionuclide diffusion.
Jonny Rutqvist, Yves Guglielmi, Hao Xu, Yuan Tian, Piotr Zarzycki, Hang Deng, Pei Li, Mengsu Hu, Peter Nico, Sharon Borglin, Patricia Fox, Tsubasa Sasaki, Jens Birkholzer. 2020, Investigation of Coupled Processes in Argillite Rock: FY20 Progress
Milestone report for EBS R&D: Engineered Barrier System Research Activities at LBNL: FY20 Progress Report
Contact: Piotr Zarzycki