Abstract: Internal exposure through inhalation is one of the main sources of occupational exposures of NPP staff. In order to ensure that personnel exposure meet the requirements of regulations and standards, and be as low as reasonably achievable, airborne radioactive concentration in nuclear island building should be effectively evaluated, monitored and controlled. Based on the calculation model that is widely used to evaluate the airborne radioactive concentration in nuclear island building of NPP in normal operation, the selection process of key parameters in this calculation model is analyzed and the monitoring threshold value of airborne radioactive concentration is calculated in this paper. Suggestions on the selection of key parameters and monitoring threshold value of some airborne radioactive nuclides are finally provided for designing the threshold value of start & stop of the key ventilation system, which is helpful to accurately evaluate, monitor and control the airborne radioactive concentration in nuclear island building of HPR1000, so as to reduce the personnel exposures of NPP staff.

Key words: internal exposures through inhalation, airborne radioactive, monitoring threshold value