Design Study of Fixed-Detector Monitoring of Holdup in Ductwork

Ductwork surveys for nuclear material holdup are typically conducted manually and represent the highest level of effort for holdup monitoring. There can be hundreds of monitoring points which can be difficult to access often requiring detectors to be placed on long poles to reach the necessary measurement location. This not only results in short counting times (e.g., 6-10 seconds) due to the high number of monitoring points across the facility, but variation in the actual measurement location between each facility personnel performing the measurement as well as variation in location between each measurement cycle. These factors compound together resulting in undesirably high systematic error. Development of a real-time, in situ monitoring solution that is permanently installed at each of the monitoring locations would significantly alleviate these issues by enabling longer integration times, automated data analysis, and eliminate variations in the measurement position. Several different types of detector systems are feasible for this effort. To facilitate in optimizing the location and choice of detector type a Monte Carlo simulation has been developed. The models of the monitoring locations as well as detector types have been benchmarked against data collected from real-world source-geometry scenarios. A benchmarked model of the detectors is vital to reduce systematic uncertainties in the simulation due to manufacturing tolerances in both the detectors as well as the monitoring locations. The model will be used to inform and develop a permanently installed holdup monitoring system at nuclear facilities. The comparison between the fully developed Monte Carlo simulation of the various detector types against data collected in real-world scenarios will be presented.