Performance of Canberra TruckScan Waste Assay Measurement System - 16361

After the Fukushima accident, large (approximately cubic meter) super-sacks of potentially contaminated soil and vegetation were stored at various temporary locations throughout the prefecture. Canberra has developed the TruckScan system to perform rapid and accurate assay measurements for these waste sacks loaded on trucks to determine the individual and total sack activities for Cs-137 and Cs-134. The measurement system consists of eight 3x3 inch shielded and collimated NaI(Tl) gamma-ray detectors. Data collected with the eight detectors is analyzed using a maximum entropy fitting algorithm which optimizes and predicts the mean and maximum possible activity concentration present in each of the sacks. The algorithm uses SuperISOCS to generate detection efficiencies for each detector-sack combination in the measurement, which are then used to solve for the distribution of activity concentrations in each sack that yields the best agreement with the count rates observed in each detector. Throughout the summer and fall of 2015, a prototype system was developed and tested at Canberra's Meriden CT facility. In October 2015, the prototype system was installed and demonstrated in Japan. Results of the demonstration measurements are presented along with estimates of the total measurement uncertainty (TMU) budget. (authors)