The Impact of Thiosulfate on Corrosion of Oxide-Covered Copper
Notice bibliographique
Résumé
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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Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,001 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».