Date of Award
Master of Science (MS)
Environmental Engineering and Earth Science
Brian A Powell
Daniel I Kaplan
Studies of radionuclide concentrations in Pond B, an 82 hectare abandoned reactor cooling pond at the Savannah River Site in Aiken, South Carolina, have shown the accumulation of cesium-137 (137Cs) in the surface layers of sediments sampled from random locations within the pond. Pond B received discharged cooling water containing radionuclides from R reactor at the Savannah River Plant from 1961 until 1964, at which point the reactor ceased operation. Cesium-137, one of the fission-products released, has a significant tendency to sorb onto sediments available in aquatic ecosystems. Prior studies have demonstrated that Cs concentrations decrease in abundance with increased distance from the point of entry. Previous work has shown that thermal stratification of Pond B from April to October results in hypolimnion anoxia, which in turn leads to the release of 137Cs from bottom sediments into the water column. This suggests that seasonal variability in environmental conditions influences 137Cs mobility. The current work seeks to (1) build upon these previous studies to determine if historical observations have endured for a time period on the order of one half-life of 137Cs and (2) further elucidate the mechanisms effecting 137Cs mobility in the bottom sediments of Pond B. In this study, concentrations of 137Cs were measured in water samples and sediment cores sampled from the pond’s inlet stream as well as the open water near the outlet stream of Pond B in an effort to characterize the mobility of 137Cs, as the most recent, prior data was collected over 20 years ago. Results from the inlet stream cores indicate a pattern of preferential accumulation in the top layers of the sediment cores with an activity of approximately 16.0 Bq g-1, with decreasing concentrations to 137Cs sampled from an area closest to the outlet stream demonstrate the radionuclide’s tendency to adhere to sediment focusing processes (Pinder et al. 1995). Organic matter percentages at this location ranged from ~8 – 43% and were significantly higher than inlet stream percentages of 137Cs may accumulate in organic matter rich zones. Along with characterizing 137Cs concentrations in the pond, laboratory experiments were conducted to obtain a 137Cs Kf value of 45 L kg-1 and a diffusion rate of 1.51x10-8 m2 s-1.This evidence suggests that 137Cs distribution and concentrations have remained relatively unchanged since the 1980s and only fluctuate between the sediment-water interface as a response to seasonal variations in the pond.
Wheeler, Jessica, "Effects of Seasonal Variability on the Mobility of 137Cs in an Abandoned Reactor Cooling Pond" (2021). All Theses. 3567.