Experimental study on particle loss in horizontal straight tube of sampling system in nuclear facilities

[Background] The accurate monitoring of radioactive substances in gaseous effluents from nuclear facilities is critical for ensuring environmental safety. The gas sampling monitoring system facilitates continuous sampling and measurement of these substances. However, the deposition of gaseous effluents within the system can compromise the representativeness of the sampling results if not accurately accounted for. [Purpose] This study aims to investigate the penetration efficiency of micron aerosols in horizontal sampling pipes used in nuclear power plant chimneys and to develop a more accurate prediction model for particle deposition. The purpose of this study is to investigate the penetration efficiency of micron aerosols in horizontal sampling pipes used in nuclear power plant chimneys and to develop a more accurate prediction model for particle deposition.[Method] This paper presents an experimental study that considers the effects of effective roughness, turbulent diffusion, and gravitational settlement on particle deposition. A revised prediction formula for deposition velocity in both the diffusion region and the diffusion-collision region is proposed. The hypothesis is that effective roughness may displace the origin of the velocity profile, leading to a significant impact on deposition rates.Firstly, the TSI 3321 aerodynamic particle size spectrometer was utilized to precisely measure the penetration of the horizontal sampling pipeline for aerosols, encompassing the influence of various pipe roughnesses, aerosol particle sizes, wind speeds, and pipe diameters. Further, a modified prediction model of aerosol penetration was constructed by taking into account factors such as effective roughness, turbulent diffusion, gravitational settlement, and particle inertia. By comparing the model with this experimental data and the historical experimental data, the accuracy of the predicted settlement rate is verified, and the error was basically controlled within 10%. Finally, in combination with the model and experimental data, the impacts of wind velocity, pipe diameter, and aerosol particle size on deposition velocity and amount were analyzed. [Results] The experimental results were compared against empirical formulas and historical data, revealing that the revised formula predicts deposition velocity with an error margin of less than 10%. The study found that surface roughness variations significantly affect the flow field and wall resistance, influencing deposition rates. Even minor changes at the micron level can result in substantial differences in turbulent deposition rates. [Conclusion] The conclusions drawn from this research emphasize the substantial influence of surface roughness on particle deposition rates and highlight the existence of an optimal sampling wind speed that maximizes particle penetration in the diffusion-collision zone. For smaller particles predominantly in the diffusion region, sedimentation is primarily governed by gravity and Brownian diffusion, resulting in lower sedimentation velocities. The findings contribute to the enhancement of sampling system design and operation in nuclear facilities for more precise monitoring of gaseous effluents.