Are Underground Clay Disposal Conditions Favorable for Microbial Activity and Biocorrosion?

The French concept for geological disposal of high-level radioactive waste is based on a multi-barrier system including metallic containers confined in a claystone layer. The main alteration vector is water coming from the host rock and triggering corrosion of metallic components. Despite extreme conditions, microorganisms can adapt and survive in these environments. Anoxic corrosion of metallic containers and water radiolysis produce H2, which potentially represents an abundant energetic source for microbial development, especially in this type of environment containing low amounts of biodegradable organic matter. Moreover, formation of Fe(III)-bearing corrosion products such as magnetite (Fe3O4) can provide electron acceptors for microbial development. Therefore, biocorrosion studies are needed in order to investigate the activity of hydrogenotrophic bacteria able to reduce sulphates or Fe(III) from iron oxides (passive layer). These studies help in evaluating such microbial impacts on the long-term stability of metallic components involved in radioactive waste disposal.