Nuclear Materials Measurement Impacts on Plutonium Storage and Disposition

The Department of Energy requires accurate measur ements of special nuclear material quantities and isotopics to support material control and ac countability upon creation of an item. Usually the initial non-destructive assay measur ements meet all requirements. However, at times the measure- ments must be repeated (e.g., verification measuremen ts for intersite transfers) or more accurate measurements are required to meet a specific sp ecification (e.g., a disposition program). Savannah River Site performs remeasurements to support f eed characterization for the Mixed Oxide Fuel Fab- rication Facility and to provide verification measurements for the plutonium and enriched uranium content in packages it has received for storage pending disposition. This paper describes key factors that impede accuracy in meeting the multiple program missions, including the presence of compet- ing elements and isotopes; limited counting duration; and shielding in packages that were created decades earlier.