A comparison of 137 Cs radioactivity in localized evergreen and deciduous plant species

Abstract

A vegetation study at the Comanche Peak Steam Electric Station (CPSES) near Glen Rose, Texas was conducted in 1991 and 1992. The CPSES is a commercial nuclear power plant owned and operated by Texas Utilities Electric of Dallas, Texas. The U.S. Nuclear Regulatory Commission (USNRC) requires the CPSES to routinely sample broadleaf vegetation in place of milk samples. Few commercial dairies exist in the vicinity. Broadleaf tree species are scarce because the climate and local limestone geology, have produced a dry rolling hill topography. An evergreen juniper is the dominant tree species. Few broadleaves during the winter season have hindered year117CS round sampling. This study compares the environmental concentrations between broadleaf and evergreen foliage at CPSES. Soil 117CS concentrations from each vegetation location were also compared to the foliage 137CS concentrations. The study's objective was to determine if the deciduous and evergreen vegetation 137CS concentrations are statistically the same. If the concentrations are statistically the same, then a recommendation could be made to the CPSES for substitution of leaf type sampled. Broadleaf tree leaf samples were collected on and off CPSES. Evergreen leaf samples were collected in close proximity to broadleaf samples. The leaf and soil samples were dried and homogenized for analysis. Gamma-ray spectrometry was performed to measure 137Cs radioactivity in each leaf and soil sample. The 137CS concentrations for each leaf and soil sample were calculated and statistically compared. The mean values of the 137CS concentrations in broadleaf and evergreen foliage samples were found to be statistically the same and therefore from the same population. The individual soil sample 137CS concentration means were also statistically the same and from its own population. The foliage and soil populations, although, were found to be statistically different. This study's conclusion is that evergreen leaves from juniper trees can be used to supplement and/or substitute for the broadleaf samples-currently collected. This study may be used by CPSES to petition the USNRC for a modification of the current environmental sampling program. A change in foliage collection would allow the CPSES to better satisfy its environmental sampling regulatory requirements.