Effect of Compacted Bentonite on the Corrosion behavior of Carbon Steel as Geological Isolation Overpack Material

Abstract

ABSTRACTThe corrosion rate of carbon steel in compacted bentonite was evaluated with regard to the test period length, temperature, chemicals of solution and bulk density of compacted bentonite.The average corrosion rate decreased gradually with increasing test period up to 180 days in immersion tests. The corrosion rate of carbon steel in compacted bentonite at a dry density of 1.32g/cm3 was estimated to be about 0.01 mm/y which was one order of magnitude lower than that in bentonite slurry. No significant influence of temperature on corrosion rates was observed in compacted bentonite in the range of 50∼180 °C. Variation of kinds and concentration of anion(chloride, floride, sulfate, and carbonate)in aqueous solution did not have much influence on the corrosion rate of carbon steel.Immersion tests of carbon steel in compacted bentonite at a dry density of 0.69 ∼ 1.32 g/cm3, which was mixed with an aqueous solution(synthetic sea water and distilled water), were carried out. The corrosion rate in compacted bentonite decreased from 0.04 to 0.005mm/y as the density of bentonite increased.This result suggests that the corrosion rate of carbon steel in compacted bentonite is governed by the diffusivity of corrosive materials. In general, oxygen is the dominate factor affecting corrosion rate, therefore prediction of the average corrosion rate of carbon steel was carried out on the basis of the diffusion behavior of dissolved oxygen in compacted bentonite. The prediction agreed with experimental results.