ABSTRACT
Objective To evaluate the migration of plutonium aerosol caused by α recoil. Methods In this paper, the recoil deposition and Brownian motion of plutonium-containing nanoaerosols were simulated by Monte Carlo method. The recoil angle and the vertical first landing time of Brownian motion in the process of settling were sampled, and then the lateral displacements of Brownian motion were sampled to determine the final settling position of aerosol. Results For aerosols with particle sizes of 10-50 nm, the maximum migration distance of a single recoil settling was 1.39 μm. Brownian motion increased the migration capacity. Although there was a high likelihood that aerosols settled within 100 μm, there remained a slight probability of long-term suspension in the air. Conclusion The α recoil is one of the mechanisms of plutonium aerosol migration. An important mechanism for long-distance migration of nanoaerosols is that Brownian motion after recoil may cause them to suspend for a long time.
ABSTRACT
Objective To investigate the effects of particle size, wind speed and dumping velocity on aerosol concentration distribution during powder dumping in a reprocessing plant. Methods CeO2 powder was selected as the substitute material of PuO2. FLUENT software was used to calculate the pouring process of CeO2 powder under different operation conditions. Then the aerosol concentration distribution under different dumping speeds was measured by particle size spectrometer to verify the accuracy of simulation results. Results The particles with small particle size are more likely to be separated from the mainstream area by the drag force of the surrounding gas, and the radius of the diffusion range also increases with the decrease of the particle size. 2) When the ventilation speed is less than 1 m/s, the dust lifting can be reduced and the concentration of dust particles in the chamber can be reduced to a certain extent. 3) In the process of powder dumping, the spoon is rotated anticlockwise at a speed of 100° in 2～3 s, and less dust aerosol is produced on the right side of the tray. Conclusion When operating the powder particles with smaller particle size, more attention should be paid to the monitoring of aerosol at different positions; the change of air inlet velocity makes the flow field in glove box more complex, and the volume fraction of dust particles is related to the size and location of vortex formed by airflow. The greater the wind speed, the greater the impact on the powder dumping process. The experimental results are basically consistent with the simulation results, and the results show that the lower the dumping speed, the smaller the aerosol concentration near the tray.