Assessment of microbiological development in nuclear waste geological disposal: a geochemical modeling approach

Deep geological environments are very often poor or devoid of biodegradable organic molecules, but hydrogen could be an efficient energetic source to replace organic matter and promote redox processes such as reduction of O₂, NO₃^-, Fe³⁺, SO₄^2- and CO₂. Moreover, the accessibility and availability of H₂ and nutrients depend on gas/liquid permeability and their migration in the clay-stone porosity through the excavation damaged zone (EDZ). This study evaluates the spatial and temporal evolution of the geochemical conditions with regard to microbial development. The corrosion process in the argillite is investigated using numerical modeling over a period of 100,000 years. The development of bacterial biomass is estimated using potential redox reactions catalyzed by microorganisms and available nutrients. The simulations show that after the thermal peak (ca. 100-1000 years), physico-chemical conditions are favourable to support bacterial life. Relevant amounts of H₂ and nutrients are released and migrate over the first 2 m of the argillite. Most of the biological redox process are localised close to the container where a high amount of magnetite is produced, providing Fe(III) (electron acceptor) that favours the development of iron-reducing bacteria (IRB). (authors)