Effect of sulphide exposure on mechanical properties of CuOFP

Abstract

In Finland and Sweden nuclear waste disposal is planned to be executed according to the KBS-3-concept. In the concept copper canisters containing the used nuclear fuel are buried in 400-500 m deep in the bedrock. Eventually the surface of the copper canister will come in contact with bentonite pore water which contains corrosive species such as sulphide. In this paper the effect of exposure to sulphide containing bentonite pore water at room temperature on the mechanical properties of oxygen free phosphorous doped copper (CuOFP) was studied with standard ex situ tensile and creep tests. Stress corrosion cracking (SCC) susceptibility of CuOFP was studied with in situ slow strain rate testing (SSRT). Tensile tests performed at room temperature showed a slight trend of degradation in mechanical properties with increasing sulphide concentration. Creep tests were accelerated by performing them at an elevated temperature of T5215uC, but still within the power law creep regime. In creep tests the same kind of trend as in the tensile tests could be observed but when the results were compared to the publicly available CuOFP creep data the variations between the exposed and reference samples lay within the data scatter.

Kinetic Properties of the Passive Film on Copper in the Presence of Sulfate-Reducing Bacteria

“…Furthermore, the behavior of copper is influenced by the presence and concentration of sulfide. 11,12 All of this likely renders sulfide species key players with regards to copper canister integrity.…”

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

“…[ 19,20 ] Under anaerobic conditions, there have been reports of cracking in sulphide solutions above an apparent threshold concentration, [ 21–24 ] although the observations of cracks are not reproducible. [ 25–27 ] For reasons given below, SCC is not expected under repository conditions. MIC under biofilm: Compacted bentonite buffer material suppresses microbial activity as a result of the combined effects of (a) the high swelling pressure that exceeds the turgor pressure of the microbial cells, (b) the low water activity, both in unsaturated buffer and in saturated clay with saline pore water and (c) the absence of sufficient physical space in the pore structure. [ 15 ] In addition to these stressors, the elevated temperature, lack of nutrients and restrictive mass‐transport conditions will also contribute to the suppression of microbial activity.…”

“…[19,20] Under anaerobic conditions, there have been reports of cracking in sulphide solutions above an apparent threshold concentration, [21][22][23][24] although the observations of cracks are not reproducible. [25][26][27] For reasons given below, SCC is not expected under repository conditions.…”