Stochastic Approach for Nuclear Materials Quantification Applied on Waste Packages

Gamma ray spectrometry is a passive nondestructive assay commonly used for identification and quantification of the radionuclides present in huge complex objects such as nuclear waste packages, waste drums or glove boxes. Basic methods using empirical calibration with a standard in order to quantify the activity of nuclear materials by determining the absolute efficiency calibration coefficient are useless on non-reproducible, complex and single nuclear objects like waste packages. Package specifications change at any time. Actual quantification process uses numerical modeling of the measured scene and few available data. These data are density, material, screen, geometric shape, matrix composition, matrix and source distribution. Some of them are strongly dependent on packages data knowledge and operators backgrounds. Atomic Energy Commission (CEA) is developing a methodology to quantify nuclear materials in waste packages and waste drums without operator adjustment and package configuration knowledge. This method suggests combining a global stochastic approach with multi gamma ray emission radionuclides spectrum data. The methodology is on test to quantify activity in different kind of matrix, composition, and configuration of standard sources. Activity uncertainties are taking into account by this adjustment methodology. First experimental validation results are encouraging and discussed in this paper.