Effective Half-Life of Caesium-137 in Various Environmental Media at the Savannah River Site

Abstract

During the operational history of the Savannah River Site (SRS), many different radionuclides have been released from site facilities into the SRS environment. However, only a relatively small number of pathways, most importantly (137)Cs in fish and deer, have contributed significantly to doses and risks to the public. The "effective" half-lives (Te) of (137)Cs (which include both physical decay and environmental dispersion) in Savannah River floodplain soil and vegetation and in fish and white-tailed deer from the SRS were estimated using long-term monitoring data. For 1974-2011, the Tes of (137)Cs in Savannah River floodplain soil and vegetation were 17.0 years (95% CI = 14.2-19.9) and 13.4 years (95% CI = 10.8-16.0), respectively. These Tes were greater than in a previous study that used data collected only through 2005 as a likely result of changes in the flood regime of the Savannah River. Field analyses of (137)Cs concentrations in deer collected during yearly controlled hunts at the SRS indicated an overall Te of 15.9 years (95% CI = 12.3-19.6) for 1965-2011; however, the Te for 1990-2011 was significantly shorter (11.8 years, 95% CI = 4.8-18.8) due to an increase in the rate of (137)Cs removal. The shortest Tes were for fish in SRS streams and the Savannah River (3.5-9.0 years), where dilution and dispersal resulted in rapid (137)Cs removal. Long-term data show that Tes are significantly shorter than the physical half-life of (137)Cs in the SRS environment but that they can change over time. Therefore, it is desirable have a long period of record for calculating Tes and risky to extrapolate Tes beyond this period unless the processes governing (137)Cs removal are clearly understood.

Radionuclides of the Savannah River Site Environment: Recent Data and Monitoring Techniques in Support of WAES TTX#3

“…Shown in the gamma overflight map of SRS (Figure 3-6), much of this cesium was retained in the clayey soils/sediments of the L3R, SC, PB, and FM site streams. It has been shown that the "effective" half-life (which include both physical decay and environmental dispersion) of cesium-137 in SRS floodplain soil/sediment is about 17 years (Paller, Jannik, and Baker, 2014). So, after 3 effective half-lives since the 1960's releases, about 1/8 th of the original cesium remains in the stream beds and swamps.…”

Investigating the drivers of the unprecedented Chernobyl Power Plant Wildfire in April 2020 and its effects on 137Cs dispersal

“…To determine the spatial variation of soil 137 Cs prior to the CPPF in 2019, we applied the approach used by Ager et al (2019). Specifically, we used a point-based dataset of soil of 137 Cs from 1995 (Kashparov et al 2017) and then used these 1995 levels to estimate 2019 levels using a half-life of 17 years (Paller et al 2014; Eq. 3):…”

“…where A is 2019 contamination and A 0 is 1995 deposition values, DP (the number of years since the inventory was taken) is 24 years (1995-2019) mapping, and Te (the effective half-live) is 17 years (as suggested by Paller et al 2014). We used the empirical Bayesian kriging (EBK) interpolation method within ArcMap 10.3.1 to estimate soil 137 Cs for 2019 across the area affected by the CPPF.…”

Accumulation of Contaminants by Wild Turkeys and Potential for Consumer Exposure

“…Wildlife living near these areas are then exposed to radionuclides, and research has found that their tissues contain higher activity concentrations of these anthropogenic contaminants than wildlife living in other areas (Connelly and Markham 1983; Oldenkamp et al 2017). Because of the long half‐life of some radionuclides, such as radiocesium (Cs 137 ), contamination effects can persist in the environment for decades or more (Paller et al 2014).…”

“…The radionuclide Cs 137 can accumulate in the tissues of wildlife and can pose health risks to exposed wildlife and human consumers. When consumed, Cs 137 acts as an analog to potassium, allowing it to accumulate in muscle and other soft tissues of animals, which then act as a vector of exposure to predators and human consumers of meat (Paller et al 2014). Potassium has been found to accumulate in higher concentrations in “red” (e.g., leg) muscle compared with “white” (e.g., breast) muscle (Chutkow 1973), indicating that Cs 137 activity levels may also vary among muscle types in birds.…”