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The corrosion behavior of oxygen-free copper in an anoxic 0.1 M NaCl + 5 ϫ 10 −4 M Na 2 S solution was studied using electrochemical impedance spectroscopy, scanning electron microscopy equipped with a focused ion beam, X-ray photoelectron spectroscopy and micro X-ray diffraction. The corrosion film grew as a coherent, compact crystalline layer with a nonuniform thickness. The growth kinetics obeyed a parabolic law consistent with control by a diffusion process. Once a coherent layer was established, film growth kinetics appeared to be controlled by Cu + ion diffusion through the film. At shorter times before a coherent film was established, SH − diffusion in solution exhibited a considerable influence on the growth rate.A proposed method of disposal of Swedish/Finnish/Canadian high level nuclear waste is to place it in corrosion resistant containers and bury it 500-1000 m deep in a granitic repository. 1-4 These containers would be fabricated with an inner layer of cast iron and an outer shell of oxygen-free copper ͑30-50 mm in thickness͒ 4 and emplaced in the repository surrounded by a compacted bentonite clay with a low water permeability. The residual repository space would be backfilled with a mixture of bentonite clay and crushed granite. [2][3][4] Microorganisms are abundant in repository materials and consume oxygen 5-7 leading to the rapid establishment of anoxic conditions at the waste container surface. Consequently, the early period of oxic corrosion does not lead to the significant corrosion of the waste container. 1,8 Once oxygen is consumed, the only potential oxidant for copper is sulfide, produced by the dissolution of sulfide impurities in the bentonite and the action of sulfate reducing bacteria at locations remote from the container surface 9,10 2Cu + 2SH − → Cu 2 S + H 2 + S 2− ͓1͔Various factors, such as the mechanical pressure from the swelling bentonite and the low water activity in the bentonite clay due to the heat emitted by radionuclide decay within the nuclear fuel in the container, should ensure that there is no microbial activity in the immediate vicinity of the container. The measured sulfide concentrations for repository conditions are in the range 10 −7 to 10 −4 mol/L, 2 and container corrosion has been modeled by assuming it is controlled by the transport of this sulfide either from, or through, the clay buffer to the copper container surface. 11,12 Under these conditions, the effective diffusion coefficient for SH − is 10 −2 times smaller than its value in an open solution due to the tight porosity and tortuosity of the compacted clay. 13 A considerable effort has been expended on the corrosion of Cu in saline solutions 14 and saline solutions containing sulfide, 1,15-22 but it is not generally pertinent to the conditions we are interested in.Corrosion is driven by the reaction of protons, supplied by the dissociation of SH − , and leads to the accumulation of a copper sulfide film on the corroding Cu surface. This film is primarily chalcocite ͑Cu 2 S͒, although small amounts o...

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