Investigations of subterranean bacteria in deep crystalline bedrock and their importance for the disposal of nuclear waste

The diversity and distribution of bacteria in subterranean environments have been found to be extensive and to depend on the prevailing environmental conditions. In 1987, microbiology became a part of the Swedish scientific program for the safe disposal of high level nuclear waste (HLW). The goal of the microbiology program is to understand how subterranean bacteria will interact with the performance of a future HLW repository. It concerns several major processes that directly or indirectly may exert influence on waste canister corrosion and the mobility of radionuclides. Uptake and transport of radionuclides by bacteria seem to be negligible components for radionuclide migration, but the effect from bacterial production of complexing agent remains to be evaluated. Also, bacterial production and consumption of gases will influence radionuclide transport due to gas bubbles. Many important radionuclides are immobile at reduced conditions and mobile at oxidized conditions. Bacterial activity can, therefore, indirectly decrease the mobility of radionuclides due to consumption of oxygen and the reduction of electron accepters to species such as ferrous iron and sulfide.