The representativeness of sampling is crucial for the radiation impact assessment of airborne effluents from nuclear facilities. Irregularly-shaped chimneys (e.g., fan-shaped ones) are increasingly used in nuclear industries, posing challenges to industrial emission monitoring and the analysis of sampling representativeness. Their structures result in a complex internal flow field and uneven pollutant distribution. Current international standards do not clearly specify the sampling methods for such chimneys. This study conducts CFD simulations and analysis of sampling representativeness for a typical fan-shaped chimney. The simulation results show upward spiral eddies in the chimney, leading to significant spatial agglomeration of gaseous pollutants and aerosols with distinct distribution characteristics. The aerosol concentration is affected by velocity deviations inside the chimney and shows a highly non-uniform distribution on horizontal cross-sections of the chimney, while the gaseous pollutants are relatively uniform. This difference in the behaviors of distributions could be a co-working result of particle diameter and inertia. Based on the analysis of 5 key parameters of mixing homogeneity, 40 m is recommended as a qualified sampling height in the typical chimney. Under this scenario, a preliminary 12-point sampling layout is proposed adapting the sampling principles of current international standards for cylindrical chimneys. Nevertheless, achieving precise sampling requires additional experimental work. This study provides a reliable theoretical basis for the representative sampling of pollutants in irregularly shaped chimneys for nuclear industries and can serve as theoretical guidance for future experimental studies.
Cui et al. (Thu,) studied this question.