Abstract: Taking the release of radioactive aerosols in containment to the environment through cracks during nuclear power plant accidents as the research background, the transport and retention of aerosols in capillary tubes are numerically simulated by using driftflux model. The analysis software used in this paper was Fluent. By means of user defined functions (UDF), the transport and diffusion equation with aerosol volume concentration as independent variable was added to Fluent. The equation considered the interphase slip caused by gravity sedimentation and the aerosol deposition caused by Brownian diffusion and turbulent diffusion. The transport and deposition behaviors of aerosols are closely related to the flow of carrier gas, so it is necessary to accurately simulate and validate the gas flow in numerical simulation. In this paper, the capillary tube with a length of 12 cm and an inner diameter of 397 μm was adopted as the simulation object, because Kagoshima University has adopted this type of capillary tube to research the flow characteristics in capillary tube and the experimental results were available online. The structured grid was used for mesh generation and the number of grids is about 1.7 million. The numerical simulation results of compression flow in capillary tube are in good agreement with experimental results, which proves the accuracy of the CFD model. On this basis, this paper carries out the simulation of aerosol transport and retention under different stagnation pressures. During the simulation, the flow equation is closed and only the aerosol transport and diffusion equation is solved, so as to improve the solution speed. The simulated aerosol particle size is 2 microns and the stagnation pressure is 150700 kPa. The simulation results show that the aerosol concentration decreases gradually in the direction of gas flow, indicating that the aerosol has deposited on the capillary wall. The aerosol concentration distribution on the cross section of the capillary presents an updown symmetrical structure, indicating that the gravity deposition can be ignored. The order of aerosol turbulent diffusion rate is 10-4, while the order of Brownian diffusion rate is 10-11. Therefore, turbulent diffusion plays a leading role in the three aerosol deposition mechanisms considered in this paper. The aerosol penetration coefficient is defined as the ratio of the average aerosol concentration at the capillary outlet to the average concentration at the capillary inlet. In this paper, the variation law of the aerosol penetration coefficient with the stagnation pressure was obtained on the basis of simulation results. With the increase of the stagnation pressure, the aerosol penetration coefficient decreases continuously. When the stagnation pressure exceeds 550 kPa, the penetration coefficient is less than 0.02. Therefore, considering the aerosol retention in the gap in the radioactive consequence evaluation of serious accidents in nuclear power plants will greatly optimize the evaluation results and reduce conservatism. This study provides a new technical method for the analysis of aerosol transport and retention in the gap. Later, other deposition mechanisms will be added to the model and validated by experiments.