Study On Retention Characteristics Of Aerosol In Submerged Gas Jet

Under the condition of LOCA accident in nuclear power plant,fission products are released into the containment in the form of radioactive aerosol.The BWR nuclear power plant reduces the containment pressure and filters the radioactive aerosol by passing the steam and non condensable gas in the containment into the pressure suppression pool.When the gas velocity at the outlet of the downcomer pipe is high,the submerged gas jet would form in the pool.It is important to analyze the retention characteristics of aerosol in submerged gas jet to evaluate the radioactive level in the containment gas space.In this paper,to research the flow process of non-condensable gas submerged jet and the scrubbing efficiency of aerosols in gas submerged jet,several experiments were carried out.The effect of gas injection direction and nozzle inlet pressure on aerosol scrubbing efficiency were analyzed.In addition,a calculation model of scrubbing efficiency of aerosols in non-condensable gas submerged jet is established and the results were verified by experiments.Through the study on the flow process of non-condensable gas submerged jet,it is found that the gas-liquid interface fluctuates greatly when the gas flow state at the nozzle outlet is subcritical flow,and the gas-liquid interface is smooth under the critical flow condition.The amount of droplets in gas increases with the increase of inlet pressure.It is considered that the gas velocity is an important factor affecting the amount of droplets entrained in the jet.It is found that the scrubbing efficiency of aerosol in horizontal submerged gas jet increases with the increase of nozzle inlet pressure when the gas flow at nozzle outlet is subcritical.Under the critical flow condition,the scrubbing efficiency of aerosol in gas couldn’t increase obviously with the increase of nozzle inlet pressure,and the scrubbing efficiency is close to 100 %.The scrubbing efficiency of aerosol in vertically downward submerged gas jet also increases with the increase of inlet pressure.When the inlet pressure is low and the gas flow state is subcritical flow,the scrubbing efficiency of aerosol in non-condensable gas submerged jet could be lower than 90 %,and the effect of gas injection direction on aerosol scrubbing efficiency is obvious.When the inlet pressure is higher than 0.3 MPa,the scrubbing efficiency is close to 100 %,and the effect of gas injection direction on aerosol scrubbing efficiency is not obvious.The model established in this paper calculates the scrubbing efficiency of aerosol in submerged gas jet under different inlet pressures and gas injection directions by analyzing the interaction between entrained droplets and aerosol particles.As for the horizontal submerged gas jet,the calculation results agree well with the experimental results under different inlet pressures.As for the vertically downward submerged jet,the deviation between the calculation results and experimental results is relatively high when the inlet pressure is lower than 0.2 MPa.