Microbial metabolic potential in deep crystalline bedrock: Chapter 3

Spent nuclear fuel will be deposited in deep geological repositories in the crystalline bedrock in Finland and Sweden. The repositories rely on the multi-barrier KBS-3 concept, where the first barriers consist of copper-sheeted cast-iron canisters that contain the spent nuclear fuel rods. However, the repositories will be influenced by both abiotic and biotic factors. The repositories, when closed, will be flooded with a mixture of both the local groundwater and surface water and eventually return to an anoxic deep subsurface environment. This environment will contain microbial communities that utilize chemical components that have been produced both abiotically and biologically, which will determine the composition and size of the microbial communities in the repositories. Overtime, integrity of the storage canisters may become compromised due to, for example, microbially influenced corrosion, which may result from the corrosive nature of hydrogen sulfide produced in biological sulfate reduction. Radionuclides originating from the decay of the spent nuclear fuel may escape into the repository environment, from where they may diffuse further into the surface environment. In this chapter, we aim to shed light on some of the most important aspects of the Fennoscandian Shield deep crystalline bedrock biosphere identified to date, with examples of putative biogeochemical cycles that prevail in these environments.