Measuring Key Parameters Governing Anion Transport Through Mx-80 Bentonite

Chowdhury, F.; Rashwan, T. L.; Papry, S. A.; Behazin, M.; Keech, P. G.; Mondal, P.; Sharma, J. and Krol, M. (2023). Measuring Key Parameters Governing Anion Transport Through Mx-80 Bentonite. In: Proceedings of the Canadian Society of Civil Engineering Annual Conference 2021 (Walbridge, Scott; Nik-Bakht, Mazdak; Ng, Kelvin Tsun Wai; Shome, Manas; Alam, M. Shahria; el Damatty, Ashraf and Lovegrove, Gordon eds.), Lecture Notes in Civil Engineering, Springer, Singapore, pp. 547–558.

DOI: https://doi.org/10.1007/978-981-19-0503-2_44

Abstract

The Nuclear Waste Management Organization (NWMO) is responsible for the design and implementation of Canada’s deep geological repository (DGR), which will be constructed ~ 500 m below ground surface to safely contain and isolate used nuclear fuel. Used fuel containers (UFC), designed by NWMO as part of multi-barrier system for DGR, comprises of an inner steel core with an outer copper layer that serves as a corrosion barrier. Surrounding the UFC, a highly compacted MX-80 bentonite (HCB) is used to suppress the transport of corrosive agents to the UFC and to limit the movement of radionuclides out of the DGR, in the highly unlikely event of a UFC failure. Under anaerobic conditions, sulfate-reducing bacteria at the interface of the host rock and bentonite may produce bisulfide (HS−) that can transport to the UFC surface and corrode the copper barrier. Therefore, it is crucial to understand HS− transport mechanisms through bentonite to assess the long-term DGR performance. Due to bentonite’s low permeability, HS− transport will be diffusion-driven; therefore, the apparent diffusion coefficient and retardation are critical parameters for the DGR performance assessment. This study aims to quantify HS− diffusion through bentonite using diffusion experiments under a range of anticipated DGR conditions (e.g., temperature, ionic concentration). This paper outlines the underpinning theory, experimental methodology developed to conduct experiments, and preliminary results. Altogether, this work bolsters confidence in the experimental design and methodology that will be used to determine necessary key parameters to model reactive transport of HS− through the DGR’s bentonite barrier.

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