Year
2003
Abstract
The Integrated Waste Assay System (IWAS) is a hybrid non-destructive assay (NDA) system combining passive neutron coincidence counting, active neutron interrogation, and quantitative high-resolution gamma-ray spectroscopy. The IWAS assay chamber is based on the High Efficiency Neutron Counter (HENC) but modified to incorporate the gamma-ray spectroscopy and active neutron interrogation sub-systems. The system has been optimized to take advantage of the strength of each of the three measurement techniques over the mass range of interest. Design constraints encountered and overcome to combining these three normally incompatible systems into a single instrument are discussed. Results of the numerical modeling used in the design are compared with the measured values. The integrated approach provides a reliable assay result for a wide range of waste matrix types over the mass range from 10 mg to more than 200 grams of weapons grade plutonium in less than 20 minutes assay time. The combination of the individual assay results is performed automatically by the system software using well defined selection criteria and performance based parameters. Because the analysis is not “intelligent” there is no learned behavior and the analysis is simple to reconstruct from raw data. Calibration results and detection levels are presented for each of the analysis modes illustrating the preferred operating regions for each.