Sonochemical decontamination of magnesium and magnesium-zirconium alloy
Abstract
UNGG cladding nuclear wastes constitute a huge volume of Mg-based materials presenting economic and safety concerns particularly because of the potential generation of H$_2$ gas under deep underground disposal. Their significant decontamination would involve a safer and cheaper surface storage with a better containment of the separated long-lived radioisotopes that could enter in a classical channel. The ultrasound-assisted decontamination of genuine UNGG cladding material and surrogates (pure Mg and Mg/Zr alloy) has been investigated in mild conditions. 345 kHz sonication of these materials at 20 °C in 0.01 M oxalic acid solution leads to the golf ball shape structuring of their surface with the observation of homogenously distributed 20-40 µm diameter craters. After a thorough characterization and comparison of the ultrasound effect generated at the surface, the various samples have been artificially contaminated and characterized before treatment under ultrasound. The complete and rapid decontamination of the samples is observed under 345 kHz ultrasound in addition to the removal of the corrosion promoting carbon layer observed on the inner side of the UNGG cladding. Decontamination of Mg-based materials under ultrasound results from the controlled dissolution of the surface through acoustic cavitation phenomenon. Prolonging sonication allows the neo-formed brucite (Mg(OH)$_2$) and zirconium-based phases to accumulate at the surface, which contributes to a slight but continuous surface recontamination process resulting from the re-adsorption of uranyl cations from the solution. More generally, acoustic cavitation appears as an original, viable and advantageous alternative for the decontamination of metallic wastes generated by nuclear industry with potential financial and security benefits.
Origin : Files produced by the author(s)