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

Connaugh M Fallon; William R Bower; Brian A Powell; Francis R Livens; Ian C Lyon; Alana E McNulty; Kathryn Peruski; J Frederick W Mosselmans; Daniel I Kaplan; Daniel Grolimund; Peter Warnicke; Dario Ferreira-Sanchez; Marja Siitari Kauppi; Gianni F Vettese; Samuel Shaw; Katherine Morris; Gareth T W Law

doi:10.1016/j.scitotenv.2022.160862

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

Sci Total Environ. 2023 Mar 1:862:160862. doi: 10.1016/j.scitotenv.2022.160862. Epub 2022 Dec 12.

Authors

Connaugh M Fallon¹, William R Bower², Brian A Powell³, Francis R Livens¹, Ian C Lyon⁴, Alana E McNulty⁴, Kathryn Peruski³, J Frederick W Mosselmans⁵, Daniel I Kaplan⁶, Daniel Grolimund⁷, Peter Warnicke⁷, Dario Ferreira-Sanchez⁷, Marja Siitari Kauppi⁸, Gianni F Vettese⁸, Samuel Shaw⁴, Katherine Morris⁴, Gareth T W Law⁹

Affiliations

¹ Centre for Radiochemistry Research, Department of Chemistry, The University of Manchester, Manchester M13 9PL, UK,; Research Centre for Radwaste and Decommissioning and Williamson Research Centre, Department of Earth and Environmental Sciences, The University of Manchester, Manchester M13 9PL, UK.
² Centre for Radiochemistry Research, Department of Chemistry, The University of Manchester, Manchester M13 9PL, UK,; Radiochemistry Unit, Department of Chemistry, University of Helsinki, Helsinki 00014, Finland.
³ Department of Environmental Engineering and Earth Sciences, Department of Chemistry, Clemson University, Clemson, SC 29634, USA.
⁴ Research Centre for Radwaste and Decommissioning and Williamson Research Centre, Department of Earth and Environmental Sciences, The University of Manchester, Manchester M13 9PL, UK.
⁵ Diamond Light Source, Harwell Science and Innovations Campus, Didcot, Oxfordshire OX11 0DE, UK.
⁶ Savannah River Ecology Laboratory, University of Georgia, Aiken, SC 29808, USA.
⁷ Swiss Light Source, Paul Scherrer Institute, Villigen CH-5232, Switzerland.
⁸ Radiochemistry Unit, Department of Chemistry, University of Helsinki, Helsinki 00014, Finland.
⁹ Radiochemistry Unit, Department of Chemistry, University of Helsinki, Helsinki 00014, Finland. Electronic address: gareth.law@helsinki.fi.

PMID: 36521613
DOI: 10.1016/j.scitotenv.2022.160862

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.

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

MeSH terms

Oxidation-Reduction
Rivers
South Carolina
Spectrum Analysis
Uranium* / analysis
Water Pollutants, Radioactive* / analysis

Substances

Water Pollutants, Radioactive
Uranium