DOE OSTI2015
Increasingly, model-based methods founded in physics are employed to calibrate, or extend the calibration of, nondestructive assay (NDA) systems used to characterize materials contaminated with plutonium, uranium, and other radioactive isotopes. In addition, modeling and mathematical methods are used to establish system parameters, correction factors, and measurement uncertainty components in NDA measurements. The methods combine the characteristics of the measurement configuration (detector structure, object shape and dimensions, source-detector distance and orientation, and collimation), generator knowledge of the waste composition, and known physical properties of the system in order to establish these parameters, factors, and components. These methods offer several important benefits over traditional methods used to test, calibrate, operate, and certify radiation measurement systems. First, instruments can be set up and put into service more quickly and correctly using a model-based approach. Second, calibrations can be performed, tested, and modified with reduced use of plutonium and uranium standards when modeling and mathematical methods are employed. Also, modeled approaches avoid calibration error resulting from heterogeneous source distribution. Moreover, the parameters can be installed quickly and simply in an office setting without the need for the safety, security, and safeguards considerations that are present when standards are used. Calibrations can also be tailored to fit unique or nonstandard container configurations (for example, over-packed drums), new container types, or specialized matrices. Finally, when modeling methods are applied, correction factors and measurement uncertainty elements can be developed, tested, and validated relatively quickly and without the need for surrogate matrix materials and a large number of test measurements. A combined gamma and neutron NDA system has recently been moved from Idaho National Laboratory to the TA 55 facility at Los Alamos National Laboratory (LANL). The system will be used to assay transuranic waste packaged in drums. After the move, the system was modified to replace degraded components and improve system performance. Afterwards, it was set up to assay different container types and to extend the calibration range. Model-based approaches were used to adapt the system to its new purpose at LANL. This report will describe the setup, calibration, and certification of the combined system at LANL Included in this discussion will be the measurement applications and details of the measurement methods. The steps in these processes that involved the use of modeling and mathematical calculations to replace or supplement more traditional methods will be identified and discussed. Finally, an overarching discussion of the methods and advantages of model-based methods to establish the properties of NDA systems will be presented. We conclude that validated mathematical methods offer a robust, flexible, and mature approach which is technically defensible from first principle physics. (authors)
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗