Periodic Reporting for period 3 - MIND (Development of the safety case knowledge base about the influence of microbial processes on geological disposal of radioactive wastes)
Reporting period: 2018-06-01 to 2019-05-31
WP2: The inventory of reducing gases was compiled in order to address the geochemical constraints of biological activity. The gas phase is dominated by N2 and CH4.The boundary conditions constraining the formation of sulfide in deep geological disposal conditions have been evaluated. Presence of electron donors is one of the most important controlling factors for microbial sulfate reduction. In laboratory experiments with deep groundwater populations, acetate was overall the most efficient activator of the studied microbial communities which indicates acetate’s important role as an electron donor for different Olkiluoto deep subsurface groundwater communities. In compacted clay there are several variables of importance for bacterial life, such as clay type, pH, temperature, transport conditions, water content, pressure, pore space and pore water composition. Significant acetate formation from natural organic matter present in the clays was detected in the studied bentonites. Thus bacterial activity, is possible also at densities where sulfide production could not be detected. The microbial viability appears to be linked to the degree of saturation of the bentonite which may take several years. Sulfide has been found to reduce ferric iron in several bentonites under the formation of elemental sulphur, ferrous iron and iron sulfide. This immobilisation effect can reduce the mass of sulfide that corrode metal canisters over repository life times. A laboratory scale bentonite storage experiment to simulate bentonite behaviour in the interfaces of bentonite, host rock fractures and water flow in nuclear waste geological disposal was conducted. After one year, microcosms in MX-80 bentonite initiated both at aerobic and anaerobic conditions, no essential changes in bentonite mineralogy were found compared to the initiation of experiment. A reliable method for direct detection of bacterial presence in the bentonite was developed. This method is based on the extraction of bacteria from bentonite using density gradient centrifugation and their subsequent Live/Dead fluorescence staining. The method will be very useful for future research of bacterial presence in various clay materials. High pH conditions imposed by the OPC CEM I inhibited microbial sulfate and nitrate reduction. However, SEM analysis indicated that the high pH environment does not completely eliminate the microbial population. Interestingly, in sulfate reducing conditions, a pH decrease from 12 to pH 10 was observed in one replicate harbouring clearly a larger microbial community in the suspension on top of the cementitious material compared to the other samples.
WP3: Social scientists conducted semi structured interviews with MIND members, participated as observers and presenters at MIND meetings, and analyzed guiding RWM documents within the MIND project about the role of microbes in radioactive waste disposal. Elicited findings served as inputs for communication with project participants and civil society. Group discussions, interviews and an interactive workshop with implementers, project participants and civil society were organized. Education and training activities were initiated to dissipate the knowledge gained in the MIND project beyond the known geomicrobiology expert circles.
WP4: The project also organises an Implementers Review Board (IRB) that has advised the Technical Coordinator and the Executive Committee of MIND with critical evaluation concerning research quality and significance of outputs in relation to the endusers needs.