Microbial influenced corrosion of carbon steel in compacted buffer material composed of Kunigel V1 and sand mixture

クニゲルV1およびケイ砂の混合物で構成された圧縮緩衝材中の炭素鋼に対する微生物腐食

長岡 亨*; 平野 伸一*; 松本 伯夫*; 天野 由記   

Nagaoka, Toru*; Hirano, Shinichi*; Matsumoto, Norio*; Amano, Yuki

Radioactive waste from nuclear power generation would be overpacked in metallic material, such as carbon steel. The lifetime of metallic containment is strongly related to the corrosion rate of carbon steel in compacted buffer material. Corrosion of carbon steel buried in compacted buffer material with different dry densities in test cells was investigated in lab experiments using corrosive microbial consortium. Compacted buffer materials were incubated in nutrient medium with or without inoculation by an enriched microbial community for one year at 30C and 50C. Corrosion rates were suppressed (13.6 - 18.6 mg/year) in samples with compacted densities of 1.3 and 1.6 g/cm at 50C. In contrast, a high corrosion rate was observed in the inoculated 1.0 g/cm compacted bentonite buffer materials at 30C. Although the corrosion rate was low until the sixth month (4.6 mg/year), it significantly increased to 74.9 mg/year after one year. It is demonstrated that a sufficiently high dry density is one of the important key factor to suppress microbial activity in buffer material surrounding metal containers, because of the physical characteristics such as small pores, low water activity, less nutrient supply caused by low hydraulic conductivity.