Iodide retention characteristics on oxidized Cu coupon in saline and alkaline environments: Perspectives on high-level radioactive waste disposal

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Vol. 488; p. 150575
• Main Authors: Goo, Ja-Young, Choi, Seonggyu, Namgung, Seonyi, Jo, Yongheum, Lee, Seung Yeop, Kwon, Jang-Soon, Jo, Ho Young
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.05.2024
• Subjects: Cu canister; CuI(s); High-level radioactive waste; Iodide retention; Saline; CuI(s); Cu canister; Saline; High-level radioactive waste; Iodide retention
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2024.150575

[Display omitted] •Iodide retention by a Cu canister under potential repository conditions was studied.•CuI(s) formed on the Cu coupon surface was characterized by XRD, XPS, and TEM/SEM.•Iodide was immobilized through the formation of CuI(s) in a saline environment.•Oxidized Cu+ remained stable under saline conditions, resulting in CuI(s) formation.•The Cu canister functions as a barrier, impeding the migration of radioactive iodide. Radioactive iodine, particularly 129I, is one of the most hazardous radioisotopes found in deep geological repositories for high-level radioactive waste (HLW). This study investigated the iodide retention capacity of Cu coupons, simulating Cu canisters, under potential repository conditions. In saline environments (0.1 M NaCl + 0.01 M MgSO4), iodide was immobilized through CuI(s) formation on the oxidized surface of Cu coupons. This process was facilitated by the favorable affinity between Cu+ oxidized from the Cu coupons and I−. The iodide retention capacity of Cu coupons exhibited notable sensitivity to the pH and chemical composition of the solutions. Cu+ remained stably complexed with Cl− under saline conditions, leading to the CuI(s) formation. However, in distilled water, iodide retention decreased over time due to the transformation of CuI to CuO through Cu oxidation. In an alkaline solution (0.1 M KOH), iodide retention was negligible. These results indicate that radioactive iodide ions, released in the event of canister failure, can be effectively immobilized, and their migration to the ecosystem can be impeded through CuI(s) formation on oxidized Cu canisters in saline conditions. Consequently, Cu canisters can serve as an effective barrier against radioactive iodide migration and as a long-term isolation medium for HLW, particularly under saline conditions.