ALBERT

Description: 〈p〉Publication date: 1 December 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Journal of Nuclear Materials, Volume 526〈/p〉 〈p〉Author(s): Thomas S. Neill, Katherine Morris, Carolyn I. Pearce, Liam Abrahamsen-Mills, Libor Kovarik, Simon Kellet, Bruce Rigby, Tonya Vitova, Bianca Schacherl, Samuel Shaw〈/p〉 〈div xml:lang="en"〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉U(IV) mobility can be significantly enhanced by colloids in both engineered and natural environments. This is particularly relevant in decommissioning and clean-up of nuclear facilities, such as legacy fuel ponds and silos at the Sellafield site, UK, and in long-term radioactive waste geodisposal. In this study, the product of metallic uranium (U) corrosion under anaerobic, alkaline conditions was characterised, and the interaction of this product with silicate solutions was investigated. The U metal corrosion product consisted of crystalline UO〈sub〉2〈/sub〉 nanoparticles (5–10 nm) that aggregated to form clusters larger than 20 nm. Sequential ultrafiltration indicated that a small fraction of the U metal corrosion product was colloidal. When the uranium corrosion product was reacted with silicate solutions under anaerobic conditions, ultrafiltration indicated a stable colloidal uranium fraction was formed. Extended X-ray absorption fine structure (EXAFS) spectroscopy and high resolution TEM confirmed that the majority of U was still present as UO〈sub〉2〈/sub〉 after several months of exposure to silicate solutions, but an amorphous silica coating was present on the UO〈sub〉2〈/sub〉 surface. This silica coating is believed to be responsible for formation of the UO〈sub〉2〈/sub〉 colloid fraction. Atomic-resolution scanning TEM (STEM) indicated some migration of U into the silica-coating of the UO〈sub〉2〈/sub〉 particles as non-crystalline U(IV)-silicate, suggesting alteration of UO〈sub〉2〈/sub〉 at the UO〈sub〉2〈/sub〉-silica interface had occurred. This alteration at the UO〈sub〉2〈/sub〉-silica interface is a potential pathway to the formation of U-silicates (e.g. coffinite, USiO〈sub〉4〈/sub〉).〈/p〉〈/div〉 〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S0022311519306464-fx1.jpg" width="491" alt="Image 1" title="Image 1"〉〈/figure〉〈/p〉〈/div〉