The Impact of Thiosulfate on Corrosion of Oxide-Covered Copper
Bibliographic record
Abstract
In most countries, the selected approach for long-term disposal of high-level nuclear waste is to bury it in a deep geological repository (DGR) which will be constructed around 500 metres underground, complemented by multiple barriers to ensure safe and long-term isolation. In Canada, the used nuclear fuel will be loaded into containers, called used fuel containers (UFCs), made from steel coated with copper as the corrosion-resistant material. Initially, upon emplacement of the UFCs, the conditions in a DGR will be oxidizing, due to the presence of trapped oxygen, which will lead to the formation of an oxide/hydroxide film on the container surface. With time, the DGR environment is expected to become anoxic, whereupon the dominant cause of container degradation will be reaction with bisulfide (HS−) produced by sulfate-reducing bacteria (SRB), located remote from the UFCs. In addition, bisulfide generated by SRB may undergo oxidation through reaction with residual oxidants during the transition from oxidizing to anoxic phases or, during the anoxic period, with oxidants created by water radiolysis induced by radioactive decay. All in all, these processes will result in the formation of a mixture of oxy-sulfur species, including sulfate (SO4 2−), sulfite (SO3 2−), and thiosulfate (S2O3 2−), with thiosulfate being known as a potentially corrosive agent. This study focuses on the influence of thiosulfate on the corrosion of oxide-covered copper to probe the behaviour expected during the transition between oxic and anoxic conditions in a DGR. In this work, two types of oxide film with different compositions were grown on wrought copper in a strongly alkaline solution. One comprised a single phase Cu2O, while another one consisted of a base layer of Cu2O with some Cu(II) compounds such as CuO and Cu(OH)2 on top of it. In both cases, the oxide film was subsequently exposed to an aqueous chloride solution containing thiosulfate ions with a concentration of 1.0 ×10−3 M, and a range of electrochemical and surface analysis techniques were utilized to determine what corrosion products formed on the copper surface. Exposure of both oxide films to thiosulfate-containing solution led to changes in the morphology of the films as SEM images showed oxide destruction in some areas. Besides, the formation of Cu2S due to immersion in thiosulfate solution was confirmed by both Raman spectroscopy and XPS. However, in both cases, the amount of oxide remaining on the copper surface was higher than that of sulfur species. Moreover, the interaction of the mixed oxide with thiosulfate solution may include a galvanic process involving Cu(II) reduction, as CuO was no longer detected by Raman or XPS after the exposure to thiosulfate solution. Further investigations are underway to determine the mechanism of interaction of copper oxides with thiosulfate ions.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".