Radionuclide activity concentrations in forest surface fuels at the Savannah River Site

摘要

Background/objective: A study was undertaken at the United States Department of Energy's Savannah River Site (SRS), Aiken, South Carolina to investigate radionuclide activity concentrations in litter and duff from select areas at SRS. Litter (i.e. vegetative debris) and duff (i.e. highly decomposed vegetative debris) can often be the major fuels consumed during prescribed burns and have potential to release radiological contaminants into the environment. Methods: Repeated samples from 97 locations were collected systematically across SRS and analyzed for radionuclide activity. Radionuclide activity concentrations found in litter and duff were compared. As spatial trends were of interest, spatial distributions of radionuclide activity concentrations found in litter and duff and spatial dependency amongst the data were explored. Results: ~7Be, ~(40)K, and ~(137)Cs showed statistically significant proportional differences between litter and duff samples. Duff sample concentrations for ~(137)Cs (p < 0.0001) and ~(40)K (p = 0.0015) were statistically higher compared to litter samples. ~7Be activity concentrations were statistically higher in litter as compared to duff (p < 0.0001). For ~(40)K litter and duff samples, spatial correlation tests were not significant at p = 0.05 and the maps did not indicate any apparent high concentrations centered near possible radionuclide sources (i.e. SRS facilities). For ~7Be litter samples, significant spatial correlation was calculated (p = 0.0085). No spatial correlation was evident in the ~7Be duff samples (p = 1.0000) probably due to small sample size (n = 7). ~(137)Cs litter and duff samples showed significant spatial correlations (p < 0.0001 and p < 0.0001, respectively). Conclusions: To date, few studies characterize radionuclide activity concentrations in litter and duff, and to our knowledge none present spatial analysis. Key findings show that across SRS, ~(137)Cs is the primary radionuclide of concern, with the highest number of samples reported above MDC in litter (51.4%) and duff samples (83.2%). However, ~(137)Cs litter and duff spatial trends in the maps generated from the kriging parameters do not appear to directly link the areas with higher activity concentrations with SRS facilities. The results found herein provide valuable baseline monitoring data for future studies of forest surface fuels and can be used to evaluate changes in radioactivity in surface fuels in the southeast region of the U.S.