Detecting radioactive atmospheric releases with an UAS: In-plume fights during normal operation of a nuclear research reactor with the ARMAGED-drone and the RadDetecTIF

In this report we describe the results of a measurements campaign performed around the stack of the BR1, an Ar-41 emitting air-cooled graphite moderated research reactor. Two UAS, a DJI Matrice 100 equipped with a CsI detector (i.e. RadDetecTIF), and a DJI Flame Wheel 550 equipped with a Geiger-Muller detector (i.e. ARMAGED-Drone) are used. Using successive flights, it was possible to make a reconstruction of the plume dynamics. Maximal count rates up to 125 cps (1924 nSv/h air kerma) and 24 cps (i.e. 13 µSv/h) could be detected with both systems at different locations. A clear reconstruction of the plume characteristics (i.e. identification of the Ar-41 and shape) could be performed. The experiments also indicated that the effect of plume rise is negligible. Elevated dose rates could only be observed directly near the exit of the stack between 50 and 70m.