TOOL FOR INVENTORY DIFFERENCE EVALUATION WITH FLEXIBLE MATERIAL BALANCE AREAS

All DOE sites that process special nuclear material (SNM) are required to periodically compute and evaluate inventory differences (IDs). IDs are reported for each material balance area (MBA), and propagation of variance (POV) is used to estimate the uncertainty in the ID, sID. There is a need to report the site-wide ID, and sID, and also the complex-wide ID and sID. Toward that goal we report our progress toward extending a prototype POV tool for a single MBA to combine two or more MBAs for a within-site (or within-RIS, the reporting identification symbol for the site) POV calculation. This tool: (1) estimates the measurement uncertainty for individual measurement methods using measurement control data (this includes “remeasurement database” data that captures “item-specific” biases); (2) evaluates the measurements to get the ID, and (3) uses simple analytical expressions to estimate the total sID for a given accountability period. By using a unique item identifier, the tool can locate shipments between MBAs and cancel their impact on sID if the user chooses to combine, for example, MBA1 and MBA2. In order to combine uncertainty across MBAs we must ensure the appropriate information is available, such as which is the shipper and receiver MBA, whether the material is received at the shipper or receiver value, whether it is remeasured with the same or a better method, etc. We assume the necessary information is in an XML file (presumed to be compatible with the accountability system’s measurement module).