The Passive Neutron Albedo Reactivity technique (PNAR) was used to assay used nuclear fuel as a potential method for the measurement of fissionable material in fuel assemblies. A Monte Carlo transport code (MCNPX 2.6) was used to develop simulation models to evaluate the PNAR technique. The MCNPX simulated models consisted of two 17x17 Pressurized Water Reactor (PWR) used fuel assemblies; one with an initial 3 wt% uranium-235*, cooled for 20 years and second with an initial 4 wt% uranium-235*, cooled for 5 years. Each used fuel assembly was simulated at four different burn up rates of 15, 30, 45, and 60 GWd/tU. Four fission chamber (FC) detectors were placed around the used fuel assembly. The four FC detectors considered in this study used Highly Enriched Uranium (HEU), Uranium Dioxide (UO 2 ), Depleted Uranium (DU) and Thorium (Th) FC detectors as the neutron detection material.The purpose of this study as to understand the characteristics of PNAR method and to identify a FC detector system to analyze used nuclear fuel assemblies. Results showed HEU FC detectors responded better than the other FC detectors based on cadmium ratio and on the precision counting time. The cadmium ratio response using the PNAR measurement technique with both PWR Fuel Assemblies 1 and 2, the HEU FC detector performed 0.3% better than UO 2 , 3% better than DU and 30% better than thorium FC detectors. Based upon the detector counting time for both PWR fuel assemblies 1 and 2, the HEU FC detectoru27s counting time was less than one minute, considerably less than the other three FC detectors.
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