Detector Validation and Source Term Analysis of Uranyl Nitrate to Detect Diversion at Natural Uranium Conversion Facilities

摘要

Conversion, the process by which natural uranium ore (yellowcake) is purified and converted through a series of chemical processes into uranium hexafluoride gas (UF_6), has historically been excluded from the nuclear safeguards requirements of the ~(235)Ubased nuclear fuel cycle. With each step in the conversion process from yellowcake to feedstock for UF_6 enrichment, intermediary uranium oxide and uranium fluoride compounds become progressively attractive products for diversion toward noncompliant activity. The undeclared diversion of this product material could potentially provide feedstock for a clandestine weapons program for state or nonstate entities alike. With the changing global political environment and the increased availability of dual-use nuclear technology, the International Atomic Energy Agency (IAEA) has evolved its policies to emphasize safeguarding this potential feedstock material in response to dynamic and evolving potential diversion pathways. Oak Ridge National Laboratory (ORNL) has developed the Uranyl Nitrate Calibration Loop Equipment (UNCLE) facility to simulate the full-scale operating conditions of a purified uranium-bearing aqueous stream exiting the solvent extraction process in a natural uranium conversion plant (NUCP). This work investigates gamma-ray signatures of uranyl nitrate (UN) circulating in the UNCLE facility and evaluates detector instrumentation sensitivity to UN. These detector validation activities include assessing detector responses to the UN gamma-ray signatures for such instruments as sodium iodide and germanium detectors. The results of gamma-ray source term modeling at various concentrations of UN will be presented as part of a comprehensive validation effort employing gamma-ray detection instrumentation for the detection of diversion from declared conversion activities.