Copper will be used as an outer corrosion resistant layer on canisters for spent nuclear fuel in deep geological repositories in several countries. Under normal operating conditions, the copper surface will be exposed to ionizing radiation originating from the spent nuclear fuel. The ionizing radiation that can penetrate the canister materials is constituted of gamma and neutron radiation. At the surface, copper will either be in contact with water of with humid air depending on repository type and time after closure. Absorption of ionizing radiation by the surrounding water or humid air leads to radiolytic decomposition of water and of the constituents of air. Several of the radiolysis products are potent oxidants capable of oxidizing copper. The purely aqueous radiolysis products of prime interest are hydrogen peroxide and the hydroxyl radical while irradiation of humid air also leads to production of nitric acid. In recent years we have studied this process quite extensively. One of the most surprising finding is that the amount of corrosion products formed upon irradiation of copper in pure water exceeds the amount predicted from interfacial radiation chemistry by several order of magnitude. In this paper, a mechanism accounting for this apparent discrepancy is presented and discussed. In short, the mechanism involves an active oxide layer that facilitates oxidation of the metallic copper. The radiolytic species of primary importance in the proposed mechanism is the hydroxyl radical. The relative impact of radiolytic oxidants under different conditions will also be discussed.
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