AN ASSESSMENT METHOD TO PREDICT THE RATE OF UNRESOLVED FALSE ALARMS*

A method has been developed for the U.S. Nuclear Regulatory Commission, Office of Nuclear Material Safety and Safeguards (NRC/NMSS) to predict the rate of unresolved false alarms of material loss in a nuclear facility. The computer program DETRES-1 (for detection and response) was developed by PNL. The program first assigns the \"true\" values of control unit components receipts, shipments, beginning and ending inventories. A normal random number generator centered on the true values with an associated measurement standard deviation is used to generate \"measured values\" of each component. A loss estimator is calculated from the control unit's measured values. If the loss estimator triggers a detection alarm, a response is simulated. The response simulation is divided into two phases. The first phase is to simulate remeasurement of the components of the detection loss estimator using the same or better measurement methods or inferences from surrounding control units. If this phase of response continues to indicate a material loss, a second phase of response simulating a production shutdown and comprehensive cleanout is initiated. A new loss estimator is found, and tested against the alarm thresholds. If the estimator value is below the threshold, the original detection alarm is considered resolved; if above the threshold, an unresolved alarm has occurred. A tally is kept of valid alarms (postulated theft is an analyst option), unresolved false alarms, and failure to alarm upon a true loss. The program also contains a plantwide loss estimator with similar response and alarm resolution sequences.