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Report No.
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Corrosion Assessment of Pure Copper in Synthetic Sea Water Containing Sulfide

Kawasaki, Manabu*; Taniguchi, Naoki; Kawakami, Susumu

The immersion tests of pure copper which is one of the candidate overpack materials were carried out in synthetic sea water (SSW) and in bentonite under low oxygen atmosphere at 80 degrees Celsius with changing the sulfide concentration. As the results, corrosion rates became large with increase in sulfide concentration both in simple solution and in bentonite. The corrosion rates tended to be lowered with time in every cases. Assuming that the corrosion is controlled by diffusion of HS- in bentonite, the corrosion rates were calculated for experimental conditions of bentonite thickness and compared with the values obtained in the experiments. The calculated corrosion depths were larger than experimental results. And then assuming the actual thickness of the buffer material, the long-term corrosion depth was estimated based on the diffusion of HS- in bentonite. As the results, the corrosion depth in 1000 years was 0.5mm (HS- 0.001M), 1.76mm (HS- 0.005M), 14mm (HS- 0.1M). It is likely that the corrosion product film formed in solution was tightly adhere to surface and seemed to protective. On the other hand, only a thin film was observed in bentonite at low sulfide concentration condition, and the corrosion product film formed in high sulfide concentration condition was easily broken away from the surface. It is considered that corrosion product formed in bentonite was less protective. According to the X-ray diffraction measurement, Cu2O (cuprite) was detected in SSW without sulfide, and Cu2S (chalcocite) was detected in the presence of sulfide.

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