Microbial activity in clay barrier materials during radioactive waste disposal can lead to a violation of important physicochemical properties of the barrier system as a whole, thereby reducing the safety of the storage facility. This work evaluates the activity of the microbial complex of five bentonite and two kaolin clays. All clay materials were found to contain microorganisms, mostly with organotrophic aerobic and anaerobic metabolism capable of forming hydrogen sulfide and transforming basic and impurity clay minerals. The activity of microorganisms can increase with the ingress of degradation products of aluminophosphate matrices and cement barriers, as well as radiolysis products. For all clay the rates of microbial processes were shown to exhibit a direct correlation with the content of organic matter, kaolinite, and potassium feldspar, and an inverse correlation with montmorillonite content. A systematic methodological approach is proposed for clay materials and their susceptibility to microbial processes. The approach makes it possible, based on the content of organic matter, biophilic elements in the samples, parameters of the respiratory activity of the microbial complex, the formation of hydrogen sulfide, and other parameters, to assess in advance the possibility of using them in barriers.

This paper presents the results of microbial corrosion tests on M0-grade copper under conditions simulating a geological repository for radioactive waste at the Yeniseisky site (Krasnoyarsk Krai, Russia). The work used a microbial community sampled from a depth of 450 m and stimulated with glucose, hydrogen and sulfate under anaerobic conditions. It was shown that the maximum corrosion rate, reaching 9.8 µm/y, was achieved with the addition of sulfate (1 g/L) with the participation of microorganisms from the families Desulfomicrobiaceae, Desulfovibrionaceae and Desulfuromonadaceae. It was noted that the most important factor leading to copper corrosion was the accumulation of hydrogen sulfide during the activation of sulfate-reducing microorganisms of the genera Desulfomicrobium, Desulfovibrio and Desulfuromonas. During the development of the microbial community under these conditions, the content of copper can have a significant toxic effect at a concentration of more than 250 mg/L.

The migration of the long-lived isotope technetium-99 (half-life 2.1 × 10⁵ years) presents a significant challenge for the deep geological disposal of radioactive waste. This study investigates the immobilization of technetium by carbon steel corrosion products under aerobic and anaerobic conditions simulating the Yeniseysky site (Krasnoyarsk Region, Russia), a proposed location for a Deep Geological Repository (DGR). Over time, the degradation of barrier materials is expected to allow low-salinity solutions to be brought into contact St3 steel, the intended container material for vitrified radioactive waste in the Russian context, leading to crevice corrosion. The findings demonstrate that carbon steel containers act not merely as a physical barrier but also as a chemical barrier by facilitating the reductive immobilization of technetium. The most effective reduction of technetium was observed in the presence of ferrihydrite as a corrosion product under both aerobic and anaerobic conditions, as indicated by distribution coefficient (K_d) values ranging from 1.4 × 10³ to 1.6 × 10³ cm³/g. However, the presence of bentonite clay can diminish the efficiency of this process by adsorbing corrosion products, resulting in a 50% reduction in the distribution coefficients. In contrast, leaching products from aluminophosphate glass and cement had a less pronounced effect on technetium immobilization, causing a decrease in distribution coefficients of no more than 30%. The results of this research can be applied to model the long-term behavior of technetium in the evolving environment of a geological radioactive waste repository.

Clay minerals are the main promising materials for engineering safety barriers in the disposal of radioactive waste in geological formations. Clays have high chemical stability, good sorption properties, and low diffusion coefficients. Bentonite clays combine the most optimal properties - high swelling pressure, low diffusion coefficients. At the moment, there is no unified international concept of the clay barrier density and its composition. Also, the parameters of the influence of biogenic processes on the properties of clay materials have not been correctly determined. It is planned to use of bentonite barrier between the metal container and the external environment in the design of the supercontainer for the new disposal of radioactive waste in the Nizhnekanskiy gneiss massif.Within the studies of microbiological processes in the Yeniseisky disposal site, big attention will be paid to clay barriers as sources of biogenic elements in the system and microflora and organic and inorganic carbon.Special attention will be paid to thermophilic microorganisms characterized by high growth rates and high levels of metabolic processes, which, along with the extreme impact of radioactive waste (temperature, gas release) on a site in the mountain range, can lead to the destruction of safety barriers.Based on the data of phylogenetic analysis of the 16S rRNA gene sequences in clay materials, which are planned to be used as a barrier material, bacteria of the fermentative type of metabolism, capable of forming biogenic gases and organic acids, sulfate-reducing microflora, and a wide variety of microorganisms of the iron cycle were found. We investigating the processes under conditions corresponding to both the internal and external conditions of the clay barrier. As a result of our studies, in model experiments, the effect of microflora activation by radiolysis products, carbon steel corrosion products, hydrogen, and carbon dioxide was found. A thermophilic microbiota was found in samples with bentonite clays of the Khakass and Dinosaur deposits cultivated at temperatures of 50, 70, 90° C. High content of aluminum and silicon amorphous oxide phases was found in the liquid phase after cultivation, and an increase in bioleaching was observed with increasing temperature. Screening of biocidal additives was performed to suppress microbial activity, primarily sulfate reduction. The most effective, thermally stable biocide with prolonged action was polyhexamethylguanidine at a concentration of 0.5 wt. %.

This work involved the laboratory modeling of biogenic and biogenically mediated corrosion of AISI 304 stainless steel under geochemical conditions representative of the geological disposal of radioactive waste at the Yeniseisky site (Russia). Experiments with a single glucose stimulation of a microbial community sampled from a depth of 450 m established that the initial dominance of organotrophic microflora (primarily genera such as Xanthobacterium, Novosphingobium, Hydrogenophaga, and Pseudomonas) during the first stage (up to 30 days) led to the formation of a microbial biofilm. This biofilm resulted in uniform surface corrosion at a rate of up to 16 µm/year, which is more than 30 times higher than the corrosion rate in the abiotic control. This acceleration is attributed to the accumulation of microbial metabolites, including acetate, ethanol, formate, succinate, n-butyrate, and lactate. The subsequent development of chemotrophic iron- and sulfur-cycling microflora (dominated by genera such as Sideroxydans, Pseudomonas, Geobacter, Desulfuromonas, Desulfovibrio, and Desulfomicrobium) during the second stage of microbial succession (days 60–120) led to the formation of a pit density 10 times greater than that in the abiotic control. It is important to note that the maximum corrosion rates and pit densities were observed upon the addition of a mixture of glucose and sulfate. An assessment of the role of various microbial metabolites and medium components using the potentiodynamic method demonstrated that the combined presence of hydrocarbonate, sulfide, and microbial metabolites in the solution caused a more than fivefold increase in the corrosion current. Thus, the results demonstrate the complex nature of corrosion processes under conditions modeling the geological disposal of radioactive waste, where biological and abiotic factors interact, creating a synergistic effect that significantly enhances corrosion.