污染场地放射性气溶胶颗粒再悬浮释放的CFD模拟研究

CFD simulation of the resuspension release of radioactive aerosol particles from contaminated sites

难以通过食物链转移的核素(如铀等),很可能通过再悬浮的气溶胶颗粒的形式被人体吸入,造成内照射。因此,研究放射性气溶胶颗粒的再悬浮行为对于控制其对人体的危害以及保障人类健康意义重大。该文使用CFD软件模拟了进风引起的放射性气溶胶颗粒的再悬浮运动过程和运动轨迹,分析了进、排风口设置对再悬浮箱体内气流场分布特征的影响。模拟结果表明:进风口风速设置为10 m/s时会引起地面上放射性气溶胶颗粒的再悬浮,且空间内气流分布均匀,颗粒再悬浮量较多;近地面处中心区域的模拟风速处于该地区地表面风速范围内,能很好地表征该地区地表风速对颗粒再悬浮的影响。该模拟研究可为放射性气溶胶颗粒的沉降和再悬浮实验设计提供依据,也可为放射性污染区域工作或者活动人员的辐射防护行动提供指导。

[Objective]Radioactive materials may enter the soil through atmospheric deposition,surface water,and groundwater pathways,resulting in radioactive contamination.Physical disturbances caused by natural winds or anthropogenic activities may cause particulate matter in the soil to be resuspended from the ground into the air.Some nuclides(e.g.,uranium) that are difficult to transfer to the human body through the food chain are likely to be inhaled in the form of resuspended particulate matter and cause internal irradiation.Therefore,the resuspension behavior of radioactive particulate matter must be investigated for the control of suspended particles.CFD(computational fluid dynamics)studies are mostly carried out on the resuspension of particulate matter in the pipe wall;only a few CFD numerical simulation studies have been conducted on the resuspension release of particulate matter from contaminated soil.[Methods]In this work,a CFD simulation of the resuspension release of radioactive aerosol particles from a contaminated site is carried out.First,the resuspension of radioactive aerosol particles caused by the air inlet is achieved,and the influence of the air inlet and exhaust outlet settings on the distribution characteristics of the airflow field is then analyzed.In the simulation,the air supply port is set as the velocity inlet,and the air velocity of the air inlet is set to 10 m/s.The air exhaust port is set as the outflow boundary,the wall is set as the solid-wall boundary condition,and the ground surface is set as the surface source for generating aerosol particles.The generated aerosol particles have a size of 2.5 μm and a density of 1.65 g/cm^(3).The discrete phase model is chosen to solve the gas-solid two-phase flow,and the transient state is used to calculate the motion-diffusion characteristics of the resuspended aerosol particles.To determine the state of particulate matter and the trajectory of the motion with time and space,the coupled SIMPLE algorithm of pressure and velocity is selected with the standard pressure and the second-order on-wind discrete format,and the turbulence model is adopted as the standard k-ε model.According to the resuspension motion of the aerosol particles,the ventilation of the air inlet violently disturbs the airflow in the box,forming an approximate left-right symmetric airflow field in the box.[Results]Simulation results show that:1) when the inlet wind speed is 10 m/s,the airflow inside the resuspension box is uniformly distributed,and the vortex flow is sufficient to resuspend the radioactive aerosol particles on the ground.In addition,the amount of resuspension of particles is large,which is convenient for aerosol sampling and measurements.2) The simulated wind speed of the resuspension box near the ground is within the range of the ground surface wind speed in the area and thus can be applied to characterize the effect of surface wind speed on the resuspension of particles in this area.[Conclusions]This simulation provides a basis for the experimental design of the deposition and resuspension of radioactive aerosol particles.The findings provide guidance for the radiation protection of people working or moving in radiation-contaminated areas.