Browsing by Author "Manninen, Anna"

In Finland, the final disposal of spent nuclear fuel is due to begin in the 2020s. The spent nuclear fuel will be stored in the deep bedrock of Olkiluoto, Eurajoki. Biological sulphate reduction is one of the most significant mechanisms possibly disrupting the integrity of the final disposal concept. Microorganisms living in groundwater may produce sulphide, which induces corrosion of the metallic waste capsules designed for spent nuclear fuel. In addition, metallic waste present in the low-level and intermediate-level nuclear waste repository may be subject to corrosion. The rate of biological sulphate reduction in groundwater samples from Olkiluoto and in waters from experimental set-ups was studied with 35SO42- -radiolabel method. Furthermore, effects of supplemental nutrients and incubation time on detected sulphate reduction rates were studied. First, the method was optimised for the oligotrophic, deep groundwaters with low cell numbers. Abundance of marker genes was determined with qPCR, including dissimilatory sulphite reductase gene dsrB (beta subunit) and 16S rRNA gene of bacteria and archaea. Several improvements were made to the sulphate reduction rate measurement method during this thesis work. The method was demonstrated to be applicable for environmental samples. However, statistical matters, such as setting the minimum detection limit, need to be considered separately for each water type studied. Due to low cell numbers of the studied waters, variation between parallel samples was considerable throughout the work. Biological sulphate reduction was detected at various sites in the repository area. Sulphate reduction rates in the studied waters varied from approximately 0 to 1 nmol cm-3 d-1, whereas sulphate reduction rate of reference strain Desulfovibrio desulfuricans was up to 24 nmol cm-3 d-1. Supplemental nutrients and incubation time had variable effects on sulphate reduction rates. Microbial communities were demonstrated to be well-adapted to changing environmental conditions, as they were able to utilise introduced nutrients. Sulphate reduction rates detected in this study were modest. However, as the time scale for nuclear waste disposal is extremely long, estimating microbial metabolism over such period is challenging.