Year
2019
Abstract
During the past three decades, International Atomic Energy Agency (IAEA) inspectors, national inspectors, and facility operators have used neutron coincidence counters and gamma-ray isotopic ratio measurements extensively to measure the plutonium content of various forms of nuclear materials in the fuel cycle. Large automated facilities for fabricating plutonium fuel present both difficulties and challenges for improved accounting of nuclear materials. The traditional methods of sample measurements, requiring the transfer of the sample from the production line to the assay measurement station, are not possible in automated facilities. The robotics used for automation require special containers for nuclear material that cannot be easily removed from the production line. Safety and radiation protection considerations also require that the assay instrumentation be installed in the fuel production lines because, in general, personnel cannot be in the fuel-handling area with nuclear material during operations. Such operational constraints are common in many of the modem facilities that have been designed for fabricating and processing plutonium fuel. A bilateral safeguards agreement between the U.S. Department of Energy (DOE) and Power Reactor and Nuclear Fuel Development Corporation (PNC) in Japan was signed to develop and implement nondestructive assay (NDA) systems to provide continuous safeguards measurements for material accountancy in the robot-automated Plutonium Fuel Fabrication Facility (PFFF). The PFFF assay systems were required to operate in unattended mode with a size and fuel mass capability to reduce the requirement for inspector's oversight of measurement operations, reduce the inspector's workload, and improve inspection efficiencies. In addition, unattended measurements become essential when facility constraints limit the access of inspectors to the operations area during material processing. Authentication techniques were incorporated into the NDA systems so that data obtained from unattended assays could be used by independent inspectors such as the IAEA. The standardized containers and robot-controlled fuel movements in automated facilities enable more accurate nondestructive assay (NDA) measurements than are possible in conventional non-automated facilities. This paper provides an overview of the key measurement systems that were designed for the inspection of the new automated plutonium processing facilities.