Overview of an Automated, Near Realtime Materials Accounting System in Use at the Savannah River Plant

A reliable material accounting system is a requirement for the operation of any nuclear facility. At the Savannah River Plant, an automated, near realtime, accounting system has been developed to provide such reliability. The system's design provides timely detection of diversion or accounting problems by monitoring the activity in 18 unit process areas (UPAs). Material balance calculations are performed for each UFA after a batch of material has completed a processing step. Small quantities of material are used for each batch, resulting in a high frequency of material balance calculations. In most cases, an inventory difference (ID) for a UPA is established at least every 24 hours. Detection of an accounting problem is further enhanced by an online measurement control program. This program evaluates the performance of most measurement equipment every 12 hours. An estimated measurement error, derived from the control tests, is maintained for each device. Error estimates are propagated when a material balance is closed to provide a realtime limit of error for the inventory difference. Frequent material balance closures require large amounts of data. To minimize false alarms, the data must be reliable and free of input errors. Solution volumes, container identifications, material weights, etc., are all collected via direct computer connections. Manual data input is used only as a backup to the automated system. Automatic data collection also provides a quick and easy method of entering accounting data. Data entry is therefore performed simultaneously with production operations, without reducing throughput. Finally, requests for analytical results required to determine nuclear material concentrations are made online. Concentrations are determined using one of ten assay devices or by analysis performed in a dedicated laboratory. When results are available, the information is posted on the accounting computer and any required adjustments are performed automatically. If necessary, material balances are reclosed to reflect the ID changes caused by a posted results.