Investigations On The Aerosol Wash-down Characteristics Model Under Wall Condensation Conditions

The harm caused by severe accidents in nuclear reactors to human beings is immeasurable.With the improvement of science and technology and human safety awareness,the prediction and prevention of severe accidents in nuclear reactors have gradually received attention.When the serious accident such as core meltdown occurs in a nuclear power plant,a large amount of radioactive material is deposited on the vertical wall of the containment or the surface of the equipment in the form of aerosols.The condensate formed by steam condensation will scour and carry aerosols away from the wall,resulting in the redistribution of radioactive source terms in space and in the pit.It is of great significance to accurately grasp the mass transfer process of aerosols under condensation wash-down conditions for post-accident radioactive evaluation.In this paper,the aerosol wash-down process under the condition of wall condensation is taken as the research background,and the aerosol wash-down experiment under the steam thermal environment is carried out.The theoretical analysis and model exploration are carried out for the condensation process of the deposition wall and the aerosol wash-down characteristics.The main results of this paper are as follows :(1)The phenomenon of condensate wash-down aerosols on horizontal and vertical walls under steam condensation environment is analyzed.It is found that the mass of aerosols on the wall decreases exponentially with time under condensation conditions.The secondary deposition of particles in condensate under horizontal wall conditions affects the aerosol washdown rate.Under vertical conditions,the aerosol wash-down rate is affected by the area share of wet zone on the wall.(2)The horizontal wall aerosol wash-down model under condensation conditions was constructed.The simulation results are consistent with the experimental results,and the model considering secondary deposition is closer to the experimental results than not considering deposition.By analyzing the horizontal model,it is found that the increase of particle diameter will significantly accelerate the aerosol wash-down process,and because the particles are more prone to secondary deposition,the aerosol wash-down rate will be reduced.With the increase of steam condensation rate,the aerosol wash-down rate of horizontal wall shows an increasing trend.(3)The vertical wall aerosol wash-down model under condensation conditions was constructed.The vertical model is in good agreement with the experimental results.The model considers the influence of the accumulation process of condensate in the early stage of condensation on the area fraction of the wet zone,which is better than the existing model prediction results based on the steady-state stage of steam condensation.The model analysis results show that the contact angle hysteresis only has a significant effect on the critical parameters and the initial condensation time t0,but the scouring process and results are mainly affected by the equilibrium contact angle.The increase of contact angle reduces the aerosol wash-down rate,while the increase of vapor condensation rate significantly increases the vertical wall aerosol wash-down rate.