Speciation of copper in high chloride concentrations, in the context of corrosion of copper canisters

Abstract

Canisters with a cast iron insert for mechanical strength and a 50‐mm thick copper shell as corrosion protection are planned to be used for disposal of spent nuclear fuel in Sweden and Finland. Chloride can be considered “beneficial”, as it promotes active dissolution of copper rather than passivation (which might result in pitting), but a high concentration of chloride in solution would increase the driving force for corrosion through the formation of soluble copper chloro complexes. Thermodynamic calculations are performed in this study with the PHREEQC software and three of its accompanying databases, and a comparison with experimental data is performed to select the database to be used when evaluating repository performance. The activity coefficient models are given special attention. For the assessment of chloride‐assisted corrosion of a KBS‐3 canister, chloride concentrations pessimistically up to 5 mol/kg are used (in Finland and Sweden, the groundwater and bentonite porewater chloride concentrations are not expected to exceed 1 mol/kg). The resulting copper solubilities are then considered in different mass transport cases.

Archives of Metallurgy and Materials

“…10b). These features can be identified as soluble CuCl 2 [52], which may enhance Cu corrosion in the solution containing chloride ions [53,54]. The surface of Cu <001> is uniformly covered with an oxide layer, which forms a compact film on the examined surface of the sample.…”

Treatment of canister corrosion in Posiva's safety case for the operating licence application

“…Examples of such processes are (i) the release of sulphide from the anaerobic dissolution of pyrite in the buffer, on account of the extremely low solubility of pyrite, [ 27 ] (ii) microbial activity in the deposition hole (for intact buffer), based on the argument that the minimum buffer dry density of 1400 kg/m 3 is sufficient to suppress microbial activity, [ 5 ] and (iii) uniform corrosion in O 2 ‐free H 2 O [ 3 ] or in anoxic saline solutions. [ 28 ]…”

Status report of the Finnish spent fuel geologic repository programme and ongoing corrosion studies

“…In addition, Posiva‐funded work has shown that the extent of corrosion of copper in anoxic chloride solutions is insignificant for chloride concentrations less than 5 mol/kg. [ 30 ]…”