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Title: Silicate stabilisation of colloidal UO2 produced by uranium metal corrosion

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 particlesmore » 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).« less

Authors:
; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
OSTI Identifier:
1558707
Alternate Identifier(s):
OSTI ID: 1601823
Report Number(s):
PNNL-SA-146561
Journal ID: ISSN 0022-3115; S0022311519306464; 151751; PII: S0022311519306464
Grant/Contract Number:  
AC05-76RL01830
Resource Type:
Published Article
Journal Name:
Journal of Nuclear Materials
Additional Journal Information:
Journal Name: Journal of Nuclear Materials Journal Volume: 526 Journal Issue: C; Journal ID: ISSN 0022-3115
Publisher:
Elsevier
Country of Publication:
Netherlands
Language:
English
Subject:
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; Uranium; silicate; corrosion; colloid; coffinite

Citation Formats

Neill, Thomas S., Morris, Katherine, Pearce, Carolyn I., Abrahamsen-Mills, Liam, Kovarik, Libor, Kellet, Simon, Rigby, Bruce, Vitova, Tonya, Schacherl, Bianca, and Shaw, Samuel. Silicate stabilisation of colloidal UO2 produced by uranium metal corrosion. Netherlands: N. p., 2019. Web. doi:10.1016/j.jnucmat.2019.151751.
Neill, Thomas S., Morris, Katherine, Pearce, Carolyn I., Abrahamsen-Mills, Liam, Kovarik, Libor, Kellet, Simon, Rigby, Bruce, Vitova, Tonya, Schacherl, Bianca, & Shaw, Samuel. Silicate stabilisation of colloidal UO2 produced by uranium metal corrosion. Netherlands. doi:10.1016/j.jnucmat.2019.151751.
Neill, Thomas S., Morris, Katherine, Pearce, Carolyn I., Abrahamsen-Mills, Liam, Kovarik, Libor, Kellet, Simon, Rigby, Bruce, Vitova, Tonya, Schacherl, Bianca, and Shaw, Samuel. Sun . "Silicate stabilisation of colloidal UO2 produced by uranium metal corrosion". Netherlands. doi:10.1016/j.jnucmat.2019.151751.
@article{osti_1558707,
title = {Silicate stabilisation of colloidal UO2 produced by uranium metal corrosion},
author = {Neill, Thomas S. and Morris, Katherine and Pearce, Carolyn I. and Abrahamsen-Mills, Liam and Kovarik, Libor and Kellet, Simon and Rigby, Bruce and Vitova, Tonya and Schacherl, Bianca and Shaw, Samuel},
abstractNote = {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).},
doi = {10.1016/j.jnucmat.2019.151751},
journal = {Journal of Nuclear Materials},
number = C,
volume = 526,
place = {Netherlands},
year = {2019},
month = {12}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
DOI: 10.1016/j.jnucmat.2019.151751

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