Detection limit variation against coarse aerosol during airborne contamination measurement with continuous air monitor

In nuclear facilities, the mandatory airborne contamination surveillance is operated by continuous air monitors (CAMs). It samples the ambient air on a filter and measures the deposited activity. It is designed to trig an alarm whenever the measured activity concentration exceeds a defined threshold. However, in some sites, such as dismantling nuclear sites, a high rate of false alarm is experienced, mainly for artificial alpha. It has been shown that false alarms are directly related to a sudden variation of the aerosol mass sizes distribution, i.e. a wrong detection limit (DL) evaluation. Experiments on the ICARE tests bench have been carried out to compare the CAM's DL and an estimated DL as a function of the aerosol characteristics, to the measured one. This new estimation shows significant improvements over the previous one and highlights the need to consider aerosol characteristics for a correct airborne contamination measurement. (authors)