The Swedish final repository and the possible risk of interactions by microbial activities

Summary The final Swedish repository for low- and intermediate-level nuclear waste is described, and some of the possible problems caused by microbial activity during storage are discussed. Microbial degradation of bitumen constitutes one of the greatest risks in the silo part of a repository. The production of carbon dioxide due to both aerobic and anaerobic processes might lead to a decrease in the pH of the water, inducing corrosion of the metal construction and storage containers, with large amounts of hydrogen gas being produced. A risk assessment for the repository must thus take into account the various activities of microbes.     

The potential significance of microbial activity in radioactive waste disposal

Summary Active microorganisms can exist in any proposed environment if the basic requirements for life are satisfied, i.e. a suitable temperature and pH, the presence of the necessary nutrients and water. If conditions are not favourable microbes may survive in a dormant state until a change will allow activity. In local pockets microenvironments may become established where microbial activity may increase leading to altered environmental conditions and to changes in the near-field, e.g. degradation and breakdown of barriers, gas generation and/or uptake and transport of nuclides.     

Disposal of low- and intermediate-level waste in Switzerland: Basic aspects of potential relevance to microbial effects

Summary Current projects for the disposal of low-and intermediate-level radioactive waste in Switzerland are based on the concept of a horizontally accessed repository under a hillside. Most of the waste to be disposed of in such a repository is operational and decommissioning waste from nuclear power plants and wastes from medicine, industry and research. This waste is generally solidified in cement and placed in steel drums or concrete containers. Once the by the anaerobic corrosion of steel and by microbial degradation of organic material, to escape from the near field. Valanginian marl, which is one of three envisaged options for the host rock, is characterized by a high carbonate content, up to 75% in some locations. The organic content of the marl is between 1% and 2%, while pyrite is present in concentrations up to 5%. The groundwater is reducing, and its pH tends to lie in the neutral to slightly alkaline range. Potentially important microbial effects on the long-term performance of the system are microbial degradation of barrier materials and organics, the effect of microorganisms on sorption, and their role as catalysts.