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Silicate stabilisation of colloidal UO2 produced by uranium metal corrosion

DOI: 10.1016/j.jnucmat.2019.151751 DOI Help

Authors: Thomas Neill (The University of Manchester) , Katherine Morris (The University of Manchester) , Carolyn I. Pearce (University of Manchester; Pacific Northwest National Laboratory) , Liam Abrahamsen-mills (National Nuclear Laboratory) , Libor Kovarik (Pacific Northwest National Laboratory) , Simon Kellet (Sellafield Ltd) , Bruce Rigby (Sellafield Ltd) , Tonya Vitova (Institute for Nuclear Waste Disposal (INE), Karlsruhe Institute of Technology) , Bianca Schacherl (Institute for Nuclear Waste Disposal (INE), Karlsruhe Institute of Technology) , Samuel Shaw (The University of Manchester)
Co-authored by industrial partner: Yes

Type: Journal Paper
Journal: Journal Of Nuclear Materials

State: Published (Approved)
Published: August 2019
Diamond Proposal Number(s): 17243

Abstract: 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 UO2 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 UO2 after several months of exposure to silicate solutions, but an amorphous silica coating was present on the UO2 surface. This silica coating is believed to be responsible for formation of the UO2 colloid fraction. Atomic-resolution scanning TEM (STEM) indicated some migration of U into the silica-coating of the UO2 particles as non-crystalline U(IV)-silicate, suggesting alteration of UO2 at the UO2-silica interface had occurred. This alteration at the UO2-silica interface is a potential pathway to the formation of U-silicates (e.g. coffinite, USiO4).

Journal Keywords: Uranium; Silicate; Corrosion; Colloid; Coffinite

Subject Areas: Materials, Chemistry, Environment

Instruments: B18-Core EXAFS