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Nagaoka, Toru*; Hirano, Shinichi*; Kosaba, Takumi*; Amano, Yuki; Mochizuki, Akihito
no journal, ,
In-situ corrosion experiment of carbon steel coupons embedded in compacted bentonite were conducted in the subsurface environment at the Horonobe underground Research Laboratory. The experiment was carried out at the 250 m depth using boreholes. To simulate a small schale of geological disposal condition, compacted bentonite coupons in the test cells were made of 100% bentonite material (Kunigel V1) with different dry densities (1.0, 1.4, 1.6, 1.8 g/cm
). After the installation, the test cells were collected after a certein period of time and measured the number of viable bacteria and analyzed microbial community stracture based on 16S rRNA gene. The carbon steel coupons were subjected to weight impairment measurements and analysis of corrosion products. The results showed that the weight of carbon steel coupons in compacted bentonite decreased at all conditions, but the amount of weight-loss tended to be greater at lower dry densities. The weight-loss was particularly large at the lowest dry density of 1.0 g/cm, and corrosion was suppressed at dry densities of 1.4 g/cm and higher. The corrosion rate tended to decrease in the later stages of the test compared to the early stages of the test. To evaluate the effect of microorganisms on the corrosion behavior, the number of viable bacteria in the collected bentonite samples was measured. The results showed that the number of aerobic bacteria tended to decrease with increasing dry density. In addition, 16S rRNA gene analysis showed that the composition of the microflora at high drying density was similar to that in the initial bentonite, while the microflora at low drying density was significantly altered. These findings suggest that microorganisms may be active in compacted bentonite at low dry density and promote corrosion.
Hirano, Shinichi*; Nagaoka, Toru*; Kosaba, Takumi*; Amano, Yuki; Mochizuki, Akihito
no journal, ,
The effects of microbial corrosion induced by microorganisms have been reported for rapid corrosion and localized corrosion that occurs in environments that are not susceptible to chemical corrosion. In geological disposal projects where radioactive waste is buried deep underground, it is considered that radioactive waste should be encapsulated in an engineered barrier (overpack (metal disposal container), buffer material) and buried underground to ensure the confinement of the radioactive waste. Since a variety of microorganisms exist in the deep subsurface, it is necessary to consider the corrosive effects of microorganisms on the metal disposal container when evaluating the confinement performance of the engineered barriers. However, there have been limited studies on corrosion by microorganisms in the subsurface. Therefore, the objective of this study was to search for the presence of microorganisms causing iron corrosion in deep groundwater at the Horonobe Underground Research Laboratory and to evaluate their corrosion activity. Microorganisms in the groundwater collected from the Horonobe Underground Research Laboratory were cultured under anaerobic conditions with carbon steel coupons. As a result, methane gas was detected in some of the groundwater culture solutions, and a prefectural weight loss and localized surface thinning of the carbon steel specimens were observed. Analysis of the microbiota in the groundwater after incubation revealed an increase in the proportion of Methanobacterium spp. in the samples with corrosive activity, so further accumulation culture was conducted using iron granules to obtain Methanobacterium isolates. Based on the results of 16S rRNA gene sequence analysis of the isolate, we designated it as Methanobacterium sp. strain H04.