Rapid detection and estimation of an unexpected atmospheric release of I

Koarashi, Jun   ; Mikami, Satoshi   ; Akiyama, Kiyomitsu; Takeishi, Minoru 

A sampling system was designed to detect rapidly an unexpected release of I during a weekly batch-sampling of a stack gas. The system consisted mainly of a sampling unit and an iodine monitor with an NaI(Tl) scintillation detector. A relationship between in situ count rate of the monitor and I activity collected in the sampling unit was derived from several set of data obtained with the system in the Tokai reprocessing plant. The system and relationship allowed us to estimate the amount of I release at an arbitrary time during the batch-sampling. A different iodine monitor with a Ge detector was also tested to overcome a difficulty in selective measurement of I with the NaI(Tl) scintillation detector in the presence of Kr in the target gas. The test demonstrated a feasibility of the real-time, Kr-interference-free monitoring of atmospheric I release.