Abstract
A nuclear fuel fabrication facility released 43,500 kg of uranium into a riparian wetland located on the Savannah River Site between 1955 and 1988. Studies were undertaken to evaluate hydrological and geochemical processes influencing uranium accumulation in the wetland. Gamma-radiation-mapping surveys were conducted by systematically walking over the contaminated wetland with backpacks equipped with global positioning systems and NaI gamma detectors. Based on maps compiled from >700,000 gamma spectra and eight sediment uranium depth profiles, it was determined that 94% of the released uranium remained in the wetland. The uranium in the wetland is concentrated in five multi-hectare areas along the stream, accounting for ∼11% of the land area adjacent to the stream. While land type (upland or wetland) and topography provided a reasonable first approximation of where much of the uranium was deposited, hydrological watershed modeling revealed that the stream velocity was especially slow through many of the hot spots. Using autoradiography combined with SEM/EDX measurements of contaminated sediments, surprisingly few hot particles were detected. Instead, uranium was evenly distributed throughout the sampled sediment, suggesting that dissolved uranium had bound to sediment particles that became suspended and later deposited in low energy (low flow velocity) portions of the stream. EXAFS suggested that U atoms were present as individual ions in disordered complexes within the sediment. Furthermore, linear combination analyses suggested that the predominant component of the U(VI) was adsorbed to sediment minerals (∼70%) and a minor component (∼30%) was associated with organic matter phases. These studies show that wetlands can be extraordinarily effective at binding and retaining uranium, thereby providing a natural barrier to the transport of uranium out of a watershed. However, significant anthropogenic or climatic changes to wetlands, such as those associated with flooding, forest fires, or land use, may disrupt the complex hydrological and biogeochemical balance necessary to maintain long-term immobilization of uranium.
| Original language | English |
|---|---|
| Article number | 105718 |
| Journal | Applied Geochemistry |
| Volume | 155 |
| DOIs | |
| State | Published - Aug 2023 |
| Externally published | Yes |
Funding
The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Daniel I. Kaplan reports financial support was provided by US Department of Energy. Kenneth Kemner reports financial support was provided by US Department of Energy. Brian A. Powell reports financial support was provided by US Department of Energy.Support for this research came from the Wetland Hydrobiogeochemistry Scientific Focus Area (SFA) at Argonne National Laboratory funded by the Environmental Systems Science Program of the Office of Biological and Environmental Research, Office of Science, U.S. Department of Energy (DOE), under contract DE-AC02-06CH11357. The participation of SREL researchers was supported through a Cooperative Agreement (DE-EM0005228) between the DOE and the University of Georgia Research Foundation. SRNL personnel received support from the LDRD program through contract LDRD-2021-00263 and a DOE contract with Savannah River Nuclear Solutions, LLC, number DE-AC09-08SR22470. Florida International University personnel received support from U.S. DOE EM under Cooperative Agreement DE-EM0005213. Funding also came from the DOE Established Program to Stimulate Competitive Research (EPSCoR) under Award Number DE–SC–00012530. Gamma and X-ray field spectroscopy surveyors include Sarah Donaher, James Foster, Kelli Trotter (all from Clemson University); and Jeffrey Lott and Michael Laird (both from SREL/University of Georgia). This research used resources of the Advanced Photon Source, a U.S. DOE Office of Science User Facility, operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We thank the MRCAT/EnviroCAT beamline staff for assistance during data collection at the synchrotron. MRCAT/EnviroCAT operations are supported by DOE and the MRCAT/EnviroCAT member institutions. Support for this research came from the Wetland Hydrobiogeochemistry Scientific Focus Area ( SFA ) at Argonne National Laboratory funded by the Environmental Systems Science Program of the Office of Biological and Environmental Research, Office of Science , U.S. Department of Energy (DOE), under contract DE-AC02-06CH11357 . The participation of SREL researchers was supported through a Cooperative Agreement ( DE-EM0005228 ) between the DOE and the University of Georgia Research Foundation . SRNL personnel received support from the LDRD program through contract LDRD-2021-00263 and a DOE contract with Savannah River Nuclear Solutions, LLC, number DE-AC09-08SR22470 . Florida International University personnel received support from U.S. DOE EM under Cooperative Agreement DE-EM0005213. Funding also came from the DOE Established Program to Stimulate Competitive Research ( EPSCoR ) under Award Number DE–SC–00012530 . Gamma and X-ray field spectroscopy surveyors include Sarah Donaher, James Foster, Kelli Trotter (all from Clemson University); and Jeffrey Lott and Michael Laird (both from SREL/University of Georgia). This research used resources of the Advanced Photon Source, a U.S. DOE Office of Science User Facility, operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We thank the MRCAT/EnviroCAT beamline staff for assistance during data collection at the synchrotron. MRCAT/EnviroCAT operations are supported by DOE and the MRCAT/EnviroCAT member institutions.
Keywords
- Gamma spectroscopy
- Mapping
- Natural attenuation
- Stream particles
- XAS