ИСТИНА

The first Russian underground repository for both high- and intermediate level radioactive waste is being built in the crystalline Archean granite gneisses at Yeniseisky site (Krasnoyarsk region, Siberia). The geological features of the Yeniseisky site have much in common with the sites at Forsmark (Sweden) (see Hedin and Olsson 2016 this issue) and at Olkiluoto (Finland). HLW will be disposed in the form of an aluminophos phate glass and ILW (with long-lived radionuclides) will be cemented [1]. Nowadays we are at the step of studies working out, including field experiments for complex safety modelling. The plan of microbiological researches is one of the clue tasks. The radioactive decay of HLW is well known to lead to containers warming up and as a consequence to activation of the thermophilic microflora at an adjacent zone of storage too. Actually, the thermophilic bacteria are the first organisms that is able to influence on the barrier after cooling below 90 С. Apparently, carbon steel is one of the main barrier constituents along with bentonite clays. It is well known that typical steel corrosion according to its' essence is accompanied by both bacterial oxidation and bacteria mediated processes. At the same time, either radiolytic hydrogen or the organic matter which is contained in clay can perform as the electrons donor. In the present study, the microbial corrosion of AISI 304 stainless steel and A570-36 carbon steel was investigated. Tests were carried out in anaerobic conditions in lack of chemical oxidizers with the use of deep bacterial communities isolated from Тau Tona mine, depth~ 1km (South Africa Republic) [2]. The natural temperature of life of these bacteria is 50 °C. The second bacterial community was isolated from surface hot spring in Tuva (Russia) [3] with natural temperature near to 45 °C. Khakass bentonite was chosen as the main component of the clay barrier and as a source of indigenous microflora .Water solution in the experiments contained 5 mmol/l Uranyl nitrate as an electron acceptor, acetate ion and trehalose were used as an electron donor. The tests temperature was 45C, the experiment lasted for 8 days. Finally, the corrosion nature of the chosen carbon steel samples in these test conditions was revealed. It is subjected to general corrosion with a relatively uniform film of corrosion products. The increase of corrosion rate by 220% was established on the samples, that were treated by the bacteria. Tau Tona cultures containing trihalose revealed the maximum corrosion rate ((48 μm/year). Microbial consortium isolated from bentonite lead to the rate corrosion 19 μm/year. Besides, the stainless steel samples during the corrosion tests showed the formation of local corrosion damage, which was identified as pitting corrosion, while the remaining surface of the steel stayed passive. The formation of pittings is likely promoted by bacteria due to the testing media contained no depassivation ions. As a result, the complex model of carbon steel corrosion is worked out. It possesses not only temperature dependence but also blocking of a surface by the newly formed corrosion products.