Implementation of a System of Gamma Imagers for Measuring
Plutonium Holdup

The Surplus Plutonium Disposition (SPD) project is an effort to dilute and dispose of many tons of weapons grade plutonium. This work will take place in a shielded glovebox to protect workers from radiological dose. Accurate measurements of the holdup, or material left behind, in the gloveboxes is important for Nuclear Material Control and Accountancy, worker dose minimization, criticality safety, and process monitoring. Shielding around the gloveboxes presents an obstacle for the traditional Generalized Gamma Holdup (GGH) method. The uncertainties associated with that method, at around 28%, are also detrimental since the amount of holdup must be kept below an established limit with a high level of confidence. Passive gamma-ray imaging provides a more complete depiction of the distribution of radioactive materials. Recent refinement of the method has demonstrated that quantitative information can be extracted from the images with a well-characterized system. A permanently installed system of gammaray imagers is currently being developed to measure plutonium holdup in the SPD gloveboxes. This paper will report on progress with the development of this system. This application requires that the features of current commercially available instruments from H3D and PHDS, optimized for measurement performance in a mobile application, be translated into the constraints of the operational environment with fixed installations. The interaction between facility constraints and measurement capabilities will be addressed. A series of measurements with plutonium sources in a mocked-up glovebox geometry with imagers mounted above the ceiling of the glovebox has been taken. Imager performance with respect to angular resolution, minimum measurement time for quantification, and signal-to-noise ratio with a multitude of sources will be evaluated for those measurements. A series of prototypes of user interfaces will be presented for display of the data to its various consumers for the purposes of Nuclear Material Control and Accountancy, worker dose minimization, criticality safety, and process monitoring.