Oxidation front and oxygen transfer in the fractured zone surrounding the Meuse/Haute-Marne URL drifts in the Callovian–Oxfordian argillaceous rock

Abstract

Deep argillaceous rocks are reducing environments. When exposed to air, reduced minerals of these rocks react with oxygen, modifying the surrounding chemical conditions. Thus, oxidation is an issue in studies about the confining properties of such rocks in the framework of geological disposal projects for radioactive waste. Previous studies in several underground research laboratories (URLs) in argillaceous rocks have shown that oxidation reactions mainly occurred in the excavation-induced fracture network surrounding the drifts. In the Callovian-Oxfordian argillaceous rock, at 2490 m in drifts from the Meuse/Haute-Marne URL, oxidized features were systematically looked for in 115 borehole cores. The concerned drifts were of various ages, from a few days to 6.5 years. After 5 months, oxidized features were encountered in numerous excavation-induced extensional fractures. In excavation-induced shear fractures, oxidized features were observed in a few borehole cores after 2 years, and they became frequent after 6 years. In all cases, the oxidized features observed were found on the fracture walls or were connected to them, and were less than 1.8 m from the drift walls. These observations about the oxidation front and its evolution over time provide insights regarding the properties of excavationinduced fractures with respect to oxygen transfer.

Stability of Clay Barriers Under Chemical Perturbations

“…Jarosite precipitation is also reported concomitantly with the absence of calcite (De Craen et al, 2008), which is in agreement with the fact that jarosite is an indicator of acidic conditions (Elwood Madden et al, 2012). Other sulfate minerals phases such as celestite, bassanite, and natrojarosite have been observed (Charpentier et al, 2004;Vinsot et al, 2014) as well as precipitation of iron hydroxides. Clay-rocks also contain organic matter (Courdouan et al, 2007;Deniau et al, 2008;Schäfer et al, 2009) that, when oxidized, releases oxygen-functionalized compounds (e.g., carboxyl groups); these compounds might be mobilized by water and participate to further reactions (Faure et al, 1999;Faure and Peiffert, 2007;Blanchart et al, 2012).…”

“…This demonstrates that these are a good path for oxygen transfer. Recently, Vinsot et al (2014) reported on a comprehensive study on oxidized features that have been observed on 115 boreholes cored in the URL (Meuse Haute Marne). Observations were made on cores sampled from a few days earlier to 6.5 years prior with some samples drilled parallel or perpendicular to the horizontal major stress field.…”

RTM for Waste Repositories

“…Another example of a coupled process is the evolution of redox conditions, a key parameter for RN solubility (Duro et al 2014) which can be modified in connection with hydraulic and mechanical process. The oxidation event that will also occur in the repository near field (Matray et al 2007;Craen et al 2008;Vinsot et al 2013;De Windt et al 2014;Vinsot et al 2014) as result of excavation and ventilation will change redox conditions. These conditions could also been modified if radiological effects are considered.…”

Corrosion of carbon steel in clay environments relevant to radioactive waste geological disposals, Mont Terri rock laboratory (Switzerland)

“…This observation is typical when clay rock, containing pyrite, is exposed to air. Indeed, pyrite oxidation enhances the production of hydrogen sulphate released in clay porewater, (Vinsot et al 2014). The oxidation likely occurred between the drilling phase and installation of the equipment.…”