Аннотация:Microbial activity in engineering clay materials of protective barriers has been studied under conditions simulating the Yeniseiskii deep underground radioactive waste repository (Zheleznogorsk, Krasnoyarsk Kray). It was established that clays with a high content of sulfur, iron, and organic carbon, as well asclays containing bioavailable mineral phases (calcites, spars, and others) can be a source of microbial gas, including methane, and also of products (for instance, hydrogen sulfide) that can corrode steels in contact with clay materials. The microbial processes in clays that are rich in biogenic elements and minerals lead with a high intensity to the dissolution of the aluminosilicate structural lattices. To prevent the microbial exposure, various biocidal additives were used: Amanat, Rancid, boric acid and polyhexamethylguanidine (PHMG). The effect of these preparations at various temperatures was analyzed. It was found that PHMG was the most effective among the tested preparations in a wide temperature range.