A Fence Line Noble Gas Monitoring System for Nuclear Power Plants
Abstract
Abstract A noble gas monitoring system has been installed at Ontario Power Generations's Pickering Nuclear Generating Station (PNGS) near Toronto, Canada. This monitoring system allows a direct measure of air kerma from external radiation instead of calculating this based on plant emission data and meteorological models. This has resulted in a reduction in the reported effective dose from external radiation by a factor of at least ten. The system consists of nine self-contained units, each with a 7.6 cm x 7.6 cm (3 inch x 3 inch) NaI(Tl) detector that is calibrated for air kerma. The 512-channel gamma ray spectral information is downloaded daily from each unit to a central computer where the data are stored and processed. A spectral stripping procedure is used to remove natural background variations from the spectral windows used to monitor xenon-133 ( 133 Xe), xenon-135 ( 135 Xe), argon-41 ( 41 Ar), and skyshine radiation from the use of radiography sources. Typical monthly minimum detection limits in air kerma are 0.3 nGy for 133 Xe, 0.7 nGy for 135 Xe, 3 nGy for 41 Ar and 2 nGy for skyshine radiation. Based on 9 months of continuous operation, the annualised air kerma due to 133 Xe, 135 Xe and 41 Ar and skyshine radiation were 7 nGy, 8 nGy, 26 nGy and 107 nGy respectively. Radiation Protection Dosimetry