Corrosion Products from Carbon Steel Formed in Compacted Bentonite under Reducing Conditions

Abstract

For safety assessment of high-level radioactive waste disposal, the sorption of radionuclides on corrosion products that migrate from overpack material into compacted bentonite and the dissolution of corrosion products, which may cause the alteration of smectite to Fe-smectite due to the increase in Fe2+ concentration in the pore water, are possibly dependent on the kinds of minerals formed in compacted bentonite as corrosion products. In this study, carbon steel, previously corroded electrochemically under aerobic conditions, was left in contact with compacted Kunigel V1 and Kunipia F under reducing conditions for 3 to 4 years at room temperature. The corrosion products, which migrated from the carbon steel into compacted bentonite, were investigated by selective dissolution analysis, which can estimate the crystal-linity of Fe-bearing compounds, and by spectrophotometry to determine the valence of iron in the corrosion products. From these analyses, the corrosion products in compacted bentonite were identified to be amorphous, noncrystalline or poorly ordered Fe(OH)2 and Fe(OH)3. Furthermore, the alteration of smectite to Fe-smectite in compacted bentonite was analyzed by X-ray diffraction (XRD). In the XRD analysis, Fe-smectite was not identified in Kunipia F from the variation in basal spacing as a function of relative humidity.