The Segmented Gamma Scanner (SGS) is a common Non-Destructive Assay (NDA) instrument that is traditionally utilized to quantify radionuclides within debris-bearing waste packaged in 55-gallon (208 liter) drums. Mirion Technologies has recently modified and characterized a traditional SGS system intended for the assay of standard 55-gallon drums to include small containers ranging in size from 5-gallon (~19 liter) pails down to one liter, or smaller, poly bottles. The modifications allow for the measurement of dense powder materials containing heavy metals from Special Nuclear Materials (SNM). The assay of small containers using the footprint of the traditional SGS is technically challenging as the change in relative sample-to-detector and sample-to-transmission-source distances can introduce significant biases in the measurement result. These biases appear at multiple points in the analyses path and include increased sensitivity to slight misalignment effects, changes in the relative field of view and how the transmission beam traverses the smaller containers differently than for larger containers. In addition, whether low-density debris or high-density powders, the interaction of the material lumpiness and self-attenuation with the observed transmission ratios is enhanced by coupling the transmission ratios and a lump correction methodology based on differential self-attenuation. Finally, the effects on container fill height, inter-layer coupling effects and emission source localization have been significantly improved utilizing an “on-the-fly” modeling approach involving In-Situ Object Counting System (ISOCS™). In this paper we describe the small container adaptations to the standard, traditional, SGS system hardware and to the newly developed analyses methodologies to overcome the associated difficulties. The methods presented are applied to SNM-bearing (Uranium) samples containing debris and powders and integrated within Mirion Technologies flagship NDA 2000 software.
Year
2020
Abstract