Sulphide‐induced stress corrosion cracking and hydrogen absorption of copper in deoxygenated water at 90°C

Abstract

Stress corrosion cracking (SCC) of oxygen‐free phosphorous‐alloyed copper was investigated in sulphide‐ and chloride‐containing deoxygenated water at 90°C with sulphide concentrations of 0.001 and 0.00001 M. Several intergranular defects were found in the specimen exposed to the high sulphide environment. Similar defects were not found in the low sulphide environment, where only slight corrosion on grain boundaries and slip lines occurred. Hydrogen content measurements show an increase in hydrogen uptake of the plastically deformed specimens, which is dependent on the sulphide concentration and on plastic deformation of copper. However, the highest hydrogen content was measured in friction stir welds, welded in air without shielding gas, and tested in the high sulphide environment. The embedded oxide particles in the weld metal act as local hydrogen trapping sites and selectively react with the sulphide solution. A relatively thick air‐formed oxide film covers the copper canisters when deposited, which transforms into a sulphide film in the repository conditions. Thus, some of the coupon specimens were pre‐oxidised. The conversion of the pre‐existing Cu2O film into Cu2S film occurs quickly and the transformation is almost 100% efficient. The structure and properties of the Cu2S films, susceptibility of copper to sulphide‐induced SCC and hydrogen uptake of copper in reducing, anoxic repository conditions are discussed.

A Review of the Effect of Irradiation on the Corrosion of Copper-Coated Used Fuel Containers

“…There is a report that the concentration of absorbed H increases with increasing cumulative dose [63]. Increased H concentrations, albeit under aggressive charging conditions, have been shown to affect the creep properties of copper [64] and have been associated with SCC in sulfide environments [65,66], neither of which should occur for the copper-coated UFC design because the copper layer is in intimate contact with the load-bearing steel substrate and because loading will be largely compressive in nature. Furthermore, the increase in absorbed H concentration due to irradiation was within the variability found for as-received copper of that grade [11].…”

Stress corrosion of copper in sulfide solutions: Variations in pH‐buffer, strain rate, and temperature

“…Atomic hydrogen in copper, from corrosion in sulfide, as a possible cause for embrittlement or cracking of copper has been suggested or implied. [ 12 ] Corrosion of copper in sulfide was shown to increase the concentration of hydrogen in copper, [ 9,10 ] and stress and strain has been shown to increase the hydrogen uptake compared to unloaded specimen. [ 10 ]…”

“…[6] Becker and Öijerholm added a phosphate buffer to about pH 7.2. [7] Recent tests for stress corrosion have been performed elsewhere, with constant strain rates [9,10] and by constant load. [11] Superficial intergranular corrosion was observed after both types of tests but no apparent degradation of the mechanical properties of copper was found.…”

Hydrogen Absorption into Copper-Coated Titanium Measured by In Situ Neutron Reflectometry and Electrochemical Impedance Spectroscopy

“…3 An aspect of the disposal plan that has received significant attention is the possibility of hydrogen absorption into the copper coatings and what effect this will have on the properties of the copper. [4][5][6][7][8] Hydrogen absorbed into copper can become trapped at grain boundaries, dislocations and other crystalline imperfections, potentially creating hydrogen-filled microvoids. 9,10 Molecular dynamic (MD) simulations of hydrogen dissolved in the lattice of copper indicate that hydrogen stabilizes the formation of vacancy clusters, which may result in void formation by impurities within the copper, such as oxygen, potentially resulting in the degradation of copper's ductility.…”

“…3,13 A series of studies have been conducted to examine the effect of hydrogen absorption into copper. [5][6][7][8] Many of these studies have been focused on the oxygen-free, phosphorus-doped (OFP) copper proposed for use in the Swedish and Finnish dual-walled copper/ cast-iron UFCs (the alloyed phosphorus is used to impart the tolerance to deformation necessary to mitigate creep in the dualwalled design). 3 With this approach, water radiolysis and corrosion of the copper by hydrosulphide (HS⁻) ions are considered the two routes most likely to generate hydrogen that could be absorbed into the copper coating, although many studies employ electrochemical charging as a way of controlling the generation of hydrogen.…”