Localised corrosion of copper canisters

Abstract

Copper canisters in a KBS-3-type underground repository will be subject to general corrosion and minor localised attack. The form of the localised corrosion will depend on the composition of the bentonite pore water in contact with the canister surface and, in particular, the pH and chloride, sulphate, and bicarbonate ion concentrations. The presence of a passive Cu 2 O/Cu(OH) 2 layer is a pre-requisite for film breakdown and pitting. Literature pitting data have been used to determine whether pitting is possible or whether the environmental conditions will favour active dissolution of the canister. It is concluded that the canister surface will corrode generally and will be subject to only minor localised corrosion in the form of surface roughening.

An update on the copper corrosion program for the long‐term management of used nuclear fuel in Canada

“…Early waste container predictions allowed for a tolerance of pitting corrosion, [ 5,6 ] but more recent reports indicate that only general copper corrosion is expected in a DGR environment(s). [ 7–9 ] Previous work demonstrates that groundwater–temperature–environmental combinations that are required to induce copper passivity, the precursor to pitting, are unlikely to occur in the Canadian DGR. [ 10 ] Thus, the NWMO has retained the previously estimated value of 100 µm for nonuniform corrosion, as this value includes the gradual roughening that the surface goes through during corrosion.…”

Computational analysis of the early stage of cuprous oxide sulphidation: a top-down process

“…This type of behaviour is believed to dominate during the main part of the repository life-time. The corrosion is assumed to be uniform since the sulphide film (mainly chalcocite, Cu 2 S) is active under the predicted steady-state conditions [3][4][5][6].…”

Probabilistic model for pitting of copper canisters

“…There are a number of sources of critical potentials for copper in relevant environments. [ 1,2 ] However, many of these studies were of limited scope with a relatively small number of E B and E RP values having been reported. The two most extensive studies are those of Cong et al [ 11 ] and Qin et al [ 13 ] Qin et al [ 13 ] determined E B and E RP values from the subset of cyclic voltammograms that exhibited passive behaviour.…”

“…Copper canisters in a planned KBS‐3 repository at the Forsmark site in Sweden are expected to be subject to general (uniform) corrosion and a limited degree of localised damage. [ 1–3 ] Based on the results of both short‐term laboratory experiments and longer term full‐scale in situ tests at the Äspö Hard Rock Laboratory, this is expected to take the form of surface roughening rather than discrete pitting corrosion. [ 2 ] The nature of the near‐surface environment is expected to result in an active copper surface rather than the passive state required for pit initiation and growth.…”

“…Pitting requires that the surface be in the passive condition. [ 1,10 ] There is a general consensus that the passivation of copper is promoted by increasing pH and/or [HCO 3 − ], while increasing [Cl − ] and [SO 4 2− ] support active dissolution. [ 11–13 ] Increasing temperature promotes active dissolution.…”