The Tennessee Valley Authority (TVA) has 17 nuclear reactors in seven separate nuclear sites that are either operating, under construction, or in various stages of licensing. As a result, TVA has developed an extensive radiological environmental monitoring program.

TVA's environmental monitoring program began in 1968 as a preoperational program around Browns Ferry Nuclear Plant to determine the levels of natural and man-made radiation present before plant operation. From a relatively modest number of 2000 samples and 8800 analyses in 1968, the number of samples has grown to 10 000 per year and the number of analyses has grown to over 42 000 per year. We expect a threefold increase over the next five years as new areas are added to the monitoring program.

Recognition of the large number of samples requiring analyses, and the desire to identify and analyze for specific isotopic content, led us to conclude early in our program that we would have to perform most analyses by gamma spectrometry. Considering costs and the instrumentation then available to us, we decided to use sodium iodide detectors, resolving the complex gamma spectra thus obtained by the use of least-squares analyses.

We are using a slightly modified form of the Alpha-M computer program developed at Oak Ridge National Laboratory by Schonfeld, and the TVA computing center at Chattanooga runs the program for us. We have also developed capabilities using germanium gamma detectors.

The laboratory recently completed detailed studies on both the germanium (lithium) and the sodium iodide (thallium) least-squares gamma analysis systems. These studies show the advantages and limitations of each system, and the application of each system to the analysis of environmental samples. By using the advantages that each system offers, we have developed a balanced approach to gamma-ray analyses.