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Vadose-zone alteration of metaschoepite and ceramic UO2 in Savannah River Site field lysimeters

DOI: 10.1016/j.scitotenv.2022.160862 DOI Help

Authors: Connaugh M. Fallon (The University of Manchester; University of Helsinki) , William R. Bower (The University of Manchester; University of Helsinki) , Brian A. Powell (Clemson University) , Francis R. Livens (The University of Manchester) , Ian C. Lyon (The University of Manchester) , Alana E. Mcnulty (The University of Manchester) , Kathryn Peruski (Clemson University) , J. Frederick W. Mosselmans (Diamond Light Source) , Daniel I. Kaplan (University of Georgia) , Daniel Grolimund (Swiss Light Source) , Peter Warnicke (Swiss Light Source) , Dario Ferreira-Sanchez (Swiss Light Source) , Marja Siitari Kauppi (University of Helsinki) , Gianni F. Vettese (University of Helsinki) , Samuel Shaw (The University of Manchester) , Katherine Morris (The University of Manchester) , Gareth T. W. Law (University of Helsinki)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Science Of The Total Environment

State: Published (Approved)
Published: December 2022
Diamond Proposal Number(s): 16611 , 16939 , 17243

Open Access Open Access

Abstract: Uranium dioxide (UO2) and metaschoepite (UO3•nH2O) particles have been identified as contaminants at nuclear sites. Understanding their behavior and impact is crucial for safe management of radioactively contaminated land and to fully understand U biogeochemistry. The Savannah River Site (SRS) (South Carolina, USA), is one such contaminated site, following historical releases of U-containing wastes to the vadose zone. Here, we present an insight into the behavior of these two particle types under dynamic conditions representative of the SRS, using field lysimeters (15 cm D x 72 cm L). Discrete horizons containing the different particle types were placed at two depths in each lysimeter (25 cm and 50 cm) and exposed to ambient rainfall for 1 year, with an aim of understanding the impact of dynamic, shallow subsurface conditions on U particle behavior and U migration. The dissolution and migration of U from the particle sources and the speciation of U throughout the lysimeters was assessed after 1 year using a combination of sediment digests, sequential extractions, and bulk and μ-focus X-ray spectroscopy. In the UO2 lysimeter, oxidative dissolution of UO2 and subsequent migration of U was observed over 1–2 cm in the direction of waterflow and against it. Sequential extractions of the UO2 sources suggest they were significantly altered over 1 year. The metaschoepite particles also showed significant dissolution with marginally enhanced U migration (several cm) from the sources. However, in both particle systems the released U was quantitively retained in sediment as a range of different U(IV) and U(VI) phases, and no detectable U was measured in the lysimeter effluent. The study provides a useful insight into U particle behavior in representative, real-world conditions relevant to the SRS, and highlights limited U migration from particle sources due to secondary reactions with vadose zone sediments over 1 year.

Journal Keywords: Uranium; X-ray absorption spectroscopy; Speciation; Groundwater; Surface water

Subject Areas: Environment, Earth Science, Chemistry

Instruments: B18-Core EXAFS

Other Facilities: X05-LA at SLS

Added On: 14/12/2022 09:57


Discipline Tags:

Desertification & Pollution Earth Sciences & Environment Radioactive Materials Materials Science Nuclear Waste Geology Geochemistry

Technical Tags:

Spectroscopy X-ray Absorption Spectroscopy (XAS) Extended X-ray Absorption Fine Structure (EXAFS) X-ray Absorption Near Edge Structure (XANES)