Abstract: The low limit detection (LLD) and the influencing factors for air effluent sampling monitoring in first stage of Fangchenggang nuclear power plant was studied. The LLD of different radioactive isotopes in air effluent with certain relative standard deviation under certain confidence level was calculated. The relationship of the relative standard deviation varying with net counting rate in different counting time was analyzed. The results showed that only when the radioactive release of air effluent approached to the calculated level, the air effluent monitoring was able to get a meaningful outcome. The analysis provides a reference for other nuclear power stations to make their own air effluent monitoring program.

Key words: Fangchenggang NPP, air effluent, low limit detection, aerosol sampling system