Hot isostatic pressing of CuI wasteforms for 129I immobilisation

Abstract

Nuclear waste streams containing radioactive iodine require disposal options that account for the long half-life of some iodine radioisotopes (129I: t1/2 ∼1.6 × 107 years) and the high mobility of iodine in most geochemical environments. One potentially attractive option is the incorporation of radioiodine into chemically stable ceramic wasteforms, such as copper iodide (CuI). Recently, a candidate copper iodide wasteform was synthesised through precipitation of iodide from solution and consolidation into a monolith, however relatively low densities were achieved. In this current work we have assessed the ability of copper to precipitate iodide and iodate from simulated waste solutions via ion exchange. The ion exchanged material was Hot Isostatically Pressed (HIPed), achieving > 98 % of the theoretical density of CuI. The HIPed ion exchanged material contained predominantly CuI, as targeted, but with additional peaks due to minor amounts of copper chloride (CuCl) and copper oxide (Cu2O). The aqueous durability of the HIPed ion exchanged material was assessed using the standard test method ASTM C1285. The thermal conductivity data of a HIPed CuI sample was then obtained over the range of 20° - 500 °C and the values ranged from ∼2 to 0.2 W/(m.K), and decreasing with temperature. This data informs the HIP cycle requirements for potential future practical application. © 2025 Elsevier B.V. All rights are reserved.