A GENERALIZED METHOD FOR FISSILE MASS CHARACTERIZATION USING SHORT-LIVED FISSION PRODUCT GAMMA MEASUREMENTS

摘要

A generalized approach of using short-lived fission product gamma-ray measurements to determine the original fissile composition in nuclear materials is being developed at the Oak Ridge National Laboratory High Flux Isotope Reactor (HFTR). This rapid and chemistry-independent method is aimed at meet nuclear forensics and safeguards nondestructive assay needs. Common Destructive Analysis (DA) techniques rely on sample dissolution, a time-consuming process which can be particularly difficult for certain sample matrices. Likewise, trace quantities of fissile material prove difficult to measure using Non-Destructive Assay (NDA) techniques due to relatively low emission rates and potentially activated materials in the sample matrix. Through use of active neutron interrogation and rapid subsequent gamma-ray measurements, the research conducted at HFIR aims to overcome these challenges. In the method being developed, the high thermal flux of HFIR and pneumatic transfer tubes at the Neutron Activation Analysis (NAA) laboratory are used to produce rapid irradiation and measurements of trace quantities of fissile material. The short-lived fission products created are used to both assay the original fissioning species and characterize mixtures of fissile material by evaluating differences in fission product yields. This analysis is conducted through SCALE modeling and simulation in combination with high-resolution gamma spectroscopy. In preliminary work, this method has been shown to be capable of analyzing nanogram quantities of ~(235)U and ~(239)Pu samples in a time period of less than ten minutes.