Exploring the Cycle of Hydrogen Gas Using Numerical Modelling in the Context of a Deep Geological Repository

Abstract

The assessment of hydrogen gas (H2) generation due to microbially influenced corrosion (MIC) is an important evaluation to build confidence in long term safety of the Canada’s proposed high level nuclear waste deep geological repository (DGR). This work presents the first numerical modelling study exploring long-term H2 dynamics under DGR environments. The key processes relevant to H2 production and consumption are identified and two numerical models are presented; one that focuses on H2 transport through the bentonite buffer and the host rock, and another that considers the production of H2 through MIC and the biotic H2 consumption (modelled through a simplified approach). The ultimate objective of this work is to investigate whether the net amount of H2 would surpass the solubility limit leading to H2 gas (bubble) formation, using conservative assumptions. The modelling study showed that long-term H2 production from MIC may depend on bisulfide (HS-) supply to the used fuel containers, H2 transport properties, and biotic H2 consumption processes. While the HS- supply could increase the H2 formation, H2 transport through the rock and biotic H2 consumption processes were shown to control the accumulation of H2. Amongst various modelling scenarios, the H2 solubility limit was never surpassed, indicating the unlikelihood of H2 gas pressure build-up in a DGR under these modelling conditions. Altogether, this study provides valuable insight into H2 production, consumption, and transport dynamics in a DGR environment by exploring various conservative scenarios.

Keywords: used nuclear fuels, bisulfide transport, deep geological repository, numerical models, hydrogen dynamics