Session: 04-01 High-Level Waste Glass & Packaging

Paper Number: 119437

119437 - Understanding Bisulfide Diffusive Transport Through Bentonite: Effect of Dry Density 

Farhana Chowdhury¹, Tarek Rashwan², Pulin Mondal¹, Mehran Behazin³, Peter Keech³,

Jitendra Sharma¹_, and Magdalena Krol¹

¹ Department of Civil Engineering, York University, 4700 Keele St, Toronto, ON M3J 1P3, Canada

² School of Engineering and Innovation, The Open University, United Kingdom

³ Nuclear Waste Management Organization, 22 St. Clair Ave. E, Toronto, ON M4T 2S3, Canada

In Canada, the Nuclear Waste Management Organization (NWMO) is responsible for the design and implementation of a deep geological repository (DGR), which will be placed ~500 m below ground surface to safely contain and isolate used nuclear fuel. The used fuel container (UFC) has been designed by NWMO as part of the engineered barrier system (EBS) for Canada’s DGR.  Adjacent to the UFC, highly compacted bentonite (HCB) is utilized to suppress the transport of corrosive agents to the UFC and to limit the movement of radionuclides out of the DGR, in the unlikely case of a breach. It is important that various UFC degradation scenarios be understood and investigated as they could compromise the long-term performance of the EBS. Under anaerobic conditions, microbiologically-influenced corrosion could occur, where sulfate-reducing bacteria produce bisulfide (HS^-) that transport through HCB and corrode the copper barrier. Therefore, it is crucial to understand HS^- transport mechanisms through the bentonite to assess the long-term performance of the EBS. Due to the low permeability of the bentonite, HS^- transport is diffusion-limited; therefore, the effective diffusion coefficient (D_e) is a critical parameter needed to assess the DGR performance. This study explored HS^- transport through MX-80 bentonite using through-diffusion experiments under various bentonite densities (1070-1600 kg/m³). Results showed that HS^- transport was highly retarded by geochemical reactions between HS^- with the HCB, which led to mineralogical changes in the bentonite. The effects of density on HS^- diffusivity were evident as increasing density led to decrease D_e values. Overall, findings suggest that HS^- transport through HCB will be highly controlled by the dry density and iron content of bentonite in the DGR environment.

Presenting Author: Farhana Chowdhury York University

Presenting Author Biography: Farhana Chowdhury is a PhD Candidate in the Civil Engineering Department, Lassonde School of Engineering, York University. Farhana received her Bachelor’s degree in Civil Engineering from Bangladesh University of Engineering and Technology (BUET). Later she was awarded with DAAD Scholarship and completed her Master’s degree from Karlsruhe Institute of Technology (KIT), Germany.
Farhana has 5 years of active teaching experience in university level. She was Assistant Professor in Water Resources Department, Chittagong University of Engineering and Technology (CUET), Bangladesh just before starting her PhD studies.
Currently Farhana is working on corrosive element transport through a compacted clay barrier in the deep geological repository for used nuclear fuel management. Farhana is co-supervised by Professors Magdalena Krol and Jit Sharma.