Canada’s plan for the long-term disposal of spent nuclear fuel in a deep geologic repository (DGR) designed by the Nuclear Waste Management Organization (NWMO) consists of a steel used fuel cannister (UFC) with a copper coating surrounded by a highly compacted bentonite (HCB) block. Under some conditions, chemical species may be generated (e.g., microbially-produced sulfide) which in principle can corrode the UFC’s copper coating. The HCB, which is part of the engineered barrier system (EBS) is designed to limit the flux of corrosive species from the surrounding subsurface environment. A thorough understanding of sulfide transport through the EBS is required to estimate UFC corrosion rates and ensure the long-term safety of the DGR. However, sulfide transport through the EBS under DGR conditions is driven by a strongly coupled, complex suite of processes including: heat transport from the UFC, multiphase flow from groundwater re-saturation, liquid-vapour water phase changes, water vapour transport, chemical reactions between sulfide and bentonite compounds, and aqueous mass transport.
A 3-D, multiphase, non-isothermal model has been developed in COMSOL Multiphysics, a finite element software package, to examine sulfide transport through the EBS under anticipated conditions of Canada’s DGR. This presentation will explore: a) The process of coupling the complex suite of processes impacting sulfide transport, b) the impact of these coupled processes on sulfide transport and DGR re-saturation, and c) presenting a rigorous verification and validation of the model with a specific focus on the multiphase flow component. Overall, the aim of this presentation is to develop confidence in sophisticated, highly coupled DGR models and to demonstrate the impact these coupled processes may have on corrosion rates and re-saturation times.
Sulfide Transport MIC Modeling
