Year one evaluation report: DELIVERABLE 3.1‐1

This year one evaluation report of MIND consists of two parts. The first part is a description of the state of the art of geological disposal of radioactive waste, with a special reference to microbiological issues. The second part is the first year evaluation of the microbial processes studied in MIND Work Packages 1 and 2. The first introductory part describes the general principles and basic concepts of geological disposal. Three main geological options are currently chosen for detailed studies in different European countries, namely crystalline rock, clay rock and salt deposits. However, as none of the lead partners is specialized in salt deposits, this will not be considered within MIND. Crystalline rock and clay rock differ substantially from each other regarding the rock type and their respective disposal concepts, including with respect to their inherent microbiology. Solid crystalline rock originates from deep hot rock melt and provides a stable non-porous barrier to isolate radioactive wastes, but the effective fluid permeability and distribution of fracture systems must be considered carefully, including the role of fractures in enabling biogeochemical processes. There are plenty of studies showing the existence of a natural deep biosphere in the fractures of crystalline rock. On the other hand, clay rocks are originally deposited in marine biosphere environment. Fluid permeability of the dense (fine-grained) clay rock is generally very low, but the total porosity is high in comparison with the non-porous crystalline rock. Still, clay rocks have excellent retardation and sealing capability. The average pore size in dense clay rock is smaller than the size of typical microorganisms, consequently the existence of viable microbial populations in consolidated clay rock is still questionable. The planned repository designs and engineered barrier systems differ for different bedrock concepts. So far the most advanced crystalline repository concepts for high-level waste are based on copper canisters embedded in bentonite buffer as diffusion and sorption barrier. The sealing capacity of the bentonite buffer and the long-term stability of copper canisters has been thoroughly studied and verified. It has been concluded that sulphidic corrosion of copper canister is a key process to be quantified. Contribution of microbially produced sulphide in the geosphere and in the repository materials has been identified as a key remaining question. The envisaged clay rock disposal designs are based on steel as canister material. Corrosion resistance of the iron-based canister materials is based on passivation of the metal surface by a protective oxide layer. In the Belgian supercontainer design for disposal of high-level waste and spent fuel, corrosion resistance is supported by the alkaline pH-value of the surrounding cementitious buffer. In the MIND project, the key microbial processes of the geological disposal of radioactive wastes are addressed. Work Package 1 focuses on microbiological processes in organic containing long-lived low- and intermediate level waste that require geological disposal. The work package includes combined irradiation and biodegradation experiments of anthropogenic organics within the waste, including halogenated polymers, cellulose, bitumen and ion exchange resins and studies of gas generation and consumption under in situ conditions. A review of anthropogenic organic wastes and associated microbiological processes is provided in MIND Deliverable D1.1-1. Work Package 2 focuses on the microbial processes in a high-level nuclear waste repository, especially the performance of bentonite buffers, metallic canisters and cementitious materials in the presence of microbes. Sources of sulphide and processes affecting sulphide formation are studied, as well as factors limiting the viability of microbes at the high swelling pressure of bentonite. Experiments are performed to study the corrosion of iron embedded in bentonite buffer and degradation of bentonite barriers.