Investigation On Removal Characteristics Of Aerosol Under Pool Scrubbing Condition

Fission products can be trapped by liquid phase due to various removal mechanisms during laden gas passing through the liquid pool,which is called pool scrubbing.Pool scrubbing is a typical phenomenon of aerosol retention process occurred in accident scenarios and corresponding mitigation measures of nuclear power plants.Thus,the study on the removal characteristics of aerosol by pool scrubbing is of great significance to the evaluation of source terms and the formulation of mitigation measures under accident conditions of nuclear power plants.However,the corresponding research is so insufficient at home and abroad.Therefore,the removal characteristics of aerosol,including insoluble aerosol and soluble aerosol,under bubble scrubbing and jet scrubbing conditions were studied by combining experimental research and theoretical analysis in this paper.The experiment is mainly carried out in pure air or nitrogen,and the main research work completed is as follows:1.The removal characteristics of insoluble aerosol by bubble scrubbing was studied.The effects of inlet aerosol concentration,aerosol size,gas flow rate and water temperature on aerosol removal efficiency were mainly analyzed.The results show that increasing aerosol inlet concentration is conducive to the removal of aerosol under the condition of high inlet aerosol concentration.The removal efficiency of aerosol decreases first and then increases with the increase of particle size,and the most easily penetrating particle size is between 0.1and 0.4μm.Aerosol removal efficiency is closely related to gas-liquid flow pattern and bubble characteristics.With the increase of water temperature,the removal efficiency of aerosol decreases,especially under the condition of low subcooling degree.Then,the obtained aerosol counting efficiency was used to verify the aerosol scrubbing model-SPARC90 model in MELCOR.Based on the experimental results and model sensitivity analysis,the SPARC90 model was modified appropriately to improve the prediction accuracy.2.Visual mechanism experiment on the removal characteristics of insoluble aerosol was carried out.The relationship between the aerosol removal characteristics and gas-liquid flow characteristics was mainly analyzed.The removal efficiency of aerosol corresponding to bubbles with different sizes was quantitatively obtained.Then,the aerosol counting efficiency obtained from the experiment was used to verify the relevant theoretical model.The results show that the calculated results of Moody model are in good agreement with the experimental results,and the Moody model can predict the removal efficiency of aerosol by bubbling scrubbing well.Based on this,three distribution parameters of aerosol size spectrum(quantitative concentration N,geometric mean diameter d_pgand geometric standard deviationσ_g)and the evolution of aerosol decontainment factor with time were deduced by using lognormal moment method,which can realize the rapid evaluation of aerosol removal characteristics by bubble scrubbing.3.The steady-state hygroscopic model of soluble aerosol based on K（?）hler’s theory was used to evaluate and improve the hygroscopic model in MELCOR with the experimental data of hygroscopic growth factor of CsI and CsOH.The influence of different parameters on the hygroscopic growth characteristics of soluble aerosol is analyzed by using the hygroscopic model of soluble aerosol,which will provide a basis for sampling measurement and analysis of bubble scrubbing characteristics of soluble aerosol.Then,the experimental study on the removal characteristics of soluble aerosol under bubble scrubbing condition was carried out.The results showed that the hygroscopic growth of soluble aerosol can be occurred in the process of bubble scrubbing.It can lead to the aerosol with small particle size original in the brown diffusion-dominant region grows up into the most easily penetrating region,which is the transition region from brown diffusion-dominant region to inertia-dominant region.Thus,the aerosol removal efficiency decreases.However,aerosol in the most easily permeable region will enter the inertia-dominant region and the removal efficiency increases.In addition,the effects of submergence depth,gas flow rate and nozzle size on bubble scrubbing characteristics of soluble aerosol were analyzed.4.Experimental study and model analysis were carried out on the removal characteristics of aerosol under horizontal submerged jet.The experimental results show that the decontamination factor of aerosol is closely related to the outlet gas velocity of nozzle and aerosol size.The decontamination factor of aerosol increases with the increase of nozzle outlet gas velocity.The decontamination factor of aerosol decreases first and then increases with the increase of particle size,and the most easily penetrating particle size is between 0.7and 1μm.A theoretical calculation model of aerosol removal efficiency under horizontal submerged jet was established.The capture mechanisms of aerosol takes into account the entrainment droplets and crest at jet wave.Then,the experimental results are used to verify the model,and the results show that the prediction accuracy of the model can meet the requirements of source term analysis.