The Impact of Cementitious Materials on the Corrosion of Copper Canisters
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7KH,PSDFWRI&HPHQWLWLRXV0DWHULDOVRQWKH&RUURVLRQRI&RSSHU&DQLVWHUV Fraser King1 and Lars Werme2 1 Integrity Corrosion Consulting Ltd, 6732 Silverview Drive NW Calgary, Alberta, Canada T3B 3K8 2 Svensk Kärnbränslehantering AB, Box 5864 SE-102 40 Stockholm, Sweden $%675$&7 Cementitious materials could be used in an underground repository as seals, bulkheads, grouts, or to provide a smooth surface for vehicles in the rooms and tunnels during repository construction. There is a possibility that an alkaline plume could be released from the cementitious materials in the repository and impact the corrosion behaviour of the canisters. The available literature information on the corrosion and electrochemical behaviour of copper in alkaline environments has been reviewed. Alkaline conditions promote passivation of the canister, whereas the presence of chloride groundwaters supports general dissolution. Localized corrosion due to an alkaline plume is considered to be unlikely because the protectiveness of the passive film (as measured by the difference between the corrosion and pitting potentials) increases with increasing pH. ,1752'8&7,21 The choice of copper as a canister material by a number of countries considering deep geological disposal of nuclear waste in stable granitic bedrock is based on the predicted excellent corrosion behaviour of this material in the expected repository environment. Copper exhibits active behaviour and corrodes uniformly in chloride-dominated environments and is not generally susceptible to localized forms of attack, such as pitting, crevice corrosion or stress corrosion cracking [1]. Furthermore, the quantity of oxidants available to support corrosion will be limited in the repository, restricted to the initially trapped atmospheric oxygen and water (in the presence of sulphide). In the latter case, the rate of corrosion will be low because it is limited by the slow rate of diffusion of HS- through the compacted bentonite in which the canister will be embedded [1]. In alkaline solutions, however, copper is rendered passive by the formation of Cu2O and/or Cu(OH)2/CuO surface films [2]. Although passivation may result in lower rates of uniform corrosion, it may also result in the canister becoming more susceptible to localized corrosion, in the form of pitting. The environment close to the canister surface is expected to be neutral to moderately alkaline, with pH values in the range pH 6-9, and possibly saline, with [Cl-] between 0.01 and 0.6 mol⋅dm-3 [1]. However, the use of concrete or other cementitious materials in the repository could result in a local increase in pH and the consequent formation of an alkaline plume that could affect the corrosion behaviour of the canister. The time at which such a plume might reach the canister, if at all, is not known. The available corrosion and electrochemical literature on the behaviour of copper in alkaline Cl- solutions under both oxic (O2-containing) and anoxic (sulphide-dominated) conditions has been reviewed and the consequences for corro
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