Remediation of 137Cs in a Former Reactor Cooling Pond at The Savannah River Site

Remediation of ¹³⁷Cs in a Former Reactor Cooling Pond at The Savannah River Site

Tracy Punshon and Domy C. Adriano

ABSTRACT

A garden crop study was initiated on ¹³⁷Cs-contaminated sediments exposed following the drawdown of a former settling pond on the Savannah River Site. Treatments consisting of a control, high rates of potassium fertilizer (‘Hi-K’), zeolite (clinoptilolite) treatment or coverage with topsoil were investigated to assess their ability to reduce uptake of ¹³⁷Cs into edible and non-edible tissues of a range of crop plants. Crops used were cabbage (Brassica oleracea var. capitata), collard (B. oleracea var. acephala), kohlrabi (B. olracea), turnip (B. campestris var. Purple Top), radish (Raphanus sativus var. Early Scarlet Globe), corn (Zea mays var. Pioneer Field Corn) and okra (Abelmoschus esculentus). Analysis of plant tissue and soil-associated ¹³⁷Cs activity was carried out throughout the study, conducted over 2.5 years (6 growing seasons). Application of topsoil was the most effective treatment, reducing ¹³⁷Cs uptake by 74.2%; bringing concentration ratios (CR) down towards regulatory limits. Hi-K and zeolite treatments were less effective, with only 45% and 38.9% reductions respectively. Background CR were high for exposed sediments, especially in cabbage and collard (2.12 and 1.75 respectively in the first growth season). Treatment efficacy changed over the course of the study topsoil and Hi-K became gradually less effective and zeolite treatments became slightly more effective. Bioturbation, or mixing of the upper layers of the soil through the activity of soil fauna and plant roots may have reduced the integrity of a topsoil cap. The inherently low K status of the extensively leached marine-derived soils of the Southeastern US may have required greater K application than was applied in this study. Site-specific studies are emphasized on Southeastern Atlantic Coastal Plain soils such as those at the Savannah River Site, where significant differences in nutrient status can influence the efficiency of certain amendments.