EVALUATION OF RADIOLOGICAL DISPERSION USING THE HAZARD PREDICTION & ASSESSMENT CAPABILITY (HPAC) CODE

This report evaluates the capabilities of the Aerial Radiological Detection Identification and Mapping System (ARDIMS) as it will be operated on the MQ-8B Fire Scout, a fully autonomous helicopter. It also compares predictions of the Hazard Prediction and Assessment Capability (HPAC) computer program to the RadPuff model’s predictions of the dispersion of a Cs137 or Co60 Radiological Dispersion Device (RDD) following ground level detonation under scenarios that included dry, light rain, moderate rain, and heavy rain. HPAC produced ground concentrations (µCi/m2) versus distance from the source were coupled with fundamental radiation transport and detector interaction parameters to determine gamma interaction rates in an airborne ARDIMS system. The ground concentration lower limit of detection (LLD) was determined using the Currie criterion for the different scenarios including the effect of different number of detectors. The analysis showed that the isotope type effects dispersion distances and detections limits, more detectors decreases the LLD proportional to the square root of the number of detectors, and that light rain will increase dispersion while heavy rain will cause faster deposition versus distance from the detonation point. RadPuff and HPAC were determined to be inconsistent models because of the analytical nature of RadPuff solutions and the probabilistic nature of HPAC solutions.