Safeguards assessment of gamma-ray detection for process monitoring at natural uranium conversion facilities

by Shaheen Azim Dewji

Institution: Georgia Tech
Department: Mechanical Engineering
Degree: PhD
Year: 2014
Keywords: Gamma-ray detection; Safeguards; Uranyl nitrate; Natural uranium; International Atomic Energy Agency; Uranium; Gamma ray detectors; Uranium compounds; Radioactive substances
Record ID: 2043994
Full text PDF: http://hdl.handle.net/1853/51794


Conversion, the process by which natural uranium ore (yellowcake) is purified and converted through a series of chemical processes into uranium hexafluoride gas (UF6), has historically been excluded from the nuclear safeguards requirements of the 235U-based nuclear fuel cycle. With each step in the conversion process from yellowcake to feedstock for UF6, intermediary uranium oxide and uranium fluoride compounds become progressively attractive products for diversion toward activities noncompliant with international treaties. The diversion of this product material could potentially provide feedstock for a clandestine or undeclared enrichment for weapons development for state or non-state entities. With the realization of this potential, the International Atomic Energy Agency (IAEA) has only recently reinterpreted its policies to emphasize safeguarding this feedstock in response to such diversion pathways. This project employs a combination of simulation models and experimental measurements to develop and validate concepts of nondestructive assay monitoring systems in a natural uranium conversion plant (NUCP). In particular, uranyl nitrate (UN) solution exiting solvent extraction was identified as a key measurement point (KMP), where gamma-ray spectroscopy was selected as the process-monitoring tool. The Uranyl Nitrate Calibration Loop Equipment (UNCLE) facility at Oak Ridge National Laboratory was employed to simulate the full-scale operating conditions of a purified uranium-bearing aqueous stream exiting the solvent extraction process in an NUCP. This work investigates gamma-ray signatures UN circulating in the UNCLE facility and evaluates various gamma-ray detector (HPGe, LaBr3 and NaI) sensitivities to UN.