Estimation methods for process holdup of special nuclear materials

The US Nuclear Regulatory Commission sponsored a research study at the Los Alamos National Laboratory to explore the possibilities of developing statistical estimation methods for materials holdup at highly enriched uranium (HEU)-processing facilities. Attempts at using historical holdup data from processing facilities and selected holdup measurements at two operating facilities confirmed the need for high-quality data and reasonable control over process parameters in developing statistical models for holdup estimations. A major effort was therefore directed at conducting large-scale experiments to demonstrate the value of statistical estimation models from experimentally measured data of good quality. Using data from these experiments, we developed statistical models to estimate residual inventories of uranium in large process equipment and facilities. Some of the important findings of this investigation are the following: prediction models for the residual holdup of special nuclear material (SNM) can be developed from good-quality historical data on holdup; holdup data from several of the equipment used at HEU-processing facilities, such as air filters, ductwork, calciners, dissolvers, pumps, pipes, and pipe fittings, readily lend themselves to statistical modeling of holdup; holdup profiles of process equipment such as glove boxes, precipitators, and rotary drum filters can change with time; therefore, good estimation of residual inventories in these types of equipment requires several measurements at the time of inventory; although measurement of residual holdup of SNM in large facilities is a challenging task, reasonable estimates of the hidden inventories of holdup to meet the regulatory requirements can be accomplished through a combination of good measurements and the use of statistical models. 44 references, 62 figures, 43 tables