SREL Reprint #3791

Temporal evolution of Pu and Cs sediment contamination in a seasonally stratified pond

Fanny Coutelot1,2, Jessica Wheeler1,2, Nancy Merino3, Daniel I. Kaplan4, Shannon Owings5,
Martial Taillefert5, Mavrik Zavarin3, Annie B. Kersting3, and Brian A. Powell1,2

1Department of Environmental Engineering and Earth Sciences, Clemson University,
Anderson, SC, United States
2Center for Nuclear Environmental Engineering and Science and Radioactive Waste Management,
Clemson University, Anderson, SC 29625, United States
3The Glenn T. Seaborg Institute, Lawrence Livermore National Laboratory, Livermore, CA, United States
4Savannah River National Laboratory, Aiken, SC, United States
5Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, United States

Abstract: There remains a lack of knowledge regarding ecosystem transfer, transport processes, and mechanisms, which influence the long-term mobility of Pu-239 and Cs-137 in natural environments. Monitoring the distribution and migration of trace radioisotopes as ecosystem tracers has the potential to provide insight into the underlying mechanisms of geochemical cycles. This study investigated the distribution of anthropogenic radionuclides Pu-239 and Cs-137 along with total organic carbon, iron, and trace element in contaminated sediments of Pond B at the Savannah River Site (SRS). Pond B received reactor cooling water from 1961 to 1964, and trace amounts of Pu-239 and Cs-137 during operations. Our study collected sediment cores to determine concentrations of Pu-239, Cs-137, and major and minor elements in solid phase, pore water and an electrochemical method was used on wet cores to determine dissolved elemental concentrations. More than 50 years after deposition, Pu-239 and Cs-137 in sediments are primarily located in the upper 5cm in area where deposition of particulate-bound contaminants was prevalent and located between 5 and 10cm in areas of high sedimentation, showing a limited migration of Pu-239 and Cs-137. A Factor analysis demonstrated different sediment facies across the pond resulting in a range of geochemical processes controlling accumulation of Pu and Cs. Highest concentrations appear to be controlled by particulate input from the influent canal, dominated by clay, silt, and sand minerals bearing Fe. Elevated Pu-239 in the sediments were observed in areas with high organic matter and higher deposition rate relative to the Pond B system near the outlet indicating strong association of Pu with OM and particulates. Therefore, organic matter cycling likely plays a role in Pu redistribution between sediment and overlying pond water, and deposition in organic rich sediments accumulating near the outlet. Though Pu appears to have been distributed throughout the pond, Cs-137 concentrations remained the highest near the influent canal.

Keywords: Plutonium; Cesium; Stratified lake; Sediment; Mobility; Pore water; Facies

SREL Reprint #3791

Coutelot, F., J. Wheeler, N. Merino, D. I. Kaplan, S. Owings, M. Taillefert, M. Zavarin, A. B. Kersting, and B. A. Powell. 2023. Temporal evolution of Pu and Cs sediment contamination in a seasonally stratified pond. Science of the Total Environment 857(159320).

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).