Impact of HPR1000 PCS heat transfer tubes on aerosol removal within containment

SUN Xiaohui; GU Haifeng; WANG Hui

doi:10.13732/j.issn.1008-5548.2025.02.015

Abstract：Objective During a severe accident at a nuclear power plant,the containment,serving as the final barrier to confine radioactive fission products,plays a crucial role in preventing the spread of radiation.Passive containment cooling systems(PCS)are incor-porated into third-generation reactors,such as AP1000 and Hualong series,to cool and depressurize the containment vessel fol-lowing a severe accident,thereby preventing containment failure.During the cooling process in Hualongreactors,temperature and gas concentration gradientsform near the PCS heat transfer tubes.These gradients drive aerosol dynamic phenomena such as diffusiophoresis and thermophoresis in the PCS,which enhance the removal of aerosols from the containment vessel during severe accidents.However,due to our insufficient understanding of PCS's enhanced aerosol removal effect,the effect has not been considered in traditional source term assessments.Therefore,research on the enhanced aerosol removal effect of PCS is benefi-cial for optimizing source term assessments and improving economic efficiency. Methods In this study,the discrete zone method was employed to solve the aerosol transport equation,focusing on the impact of PCS heat transfer tubes on aerosol removal within the containment.The theoretical calculation model was compared and verified through experiments.The calculations considered various processes affecting aerosol particles,including convection,diffusion,coagulation,condensation,nucleation,and deposition.The deposition process includes four mechanisms:gravitational set-tling,Brownian diffusion,thermophoresis,and diffusiophoresis.Experiments were conducted in a simulation chamber with a volume of approximately 12 m3,where the parameters of the heat transfer tubes were consistent with those of the prototype PCS in the Hualong pressurized reactor 1000(HPR1000).Titanium dioxide aerosols were generated using a Palas RBG2000 aerosol generator,and their particle size distribution was measured using a Palas Promo3000HP aerosol spectrometer.To investigate the impact of PCS on aerosol size evolution,experiments were conducted under two conditions:with and without heat transfer tubes.During the experiments,after introducing aerosols into the chamber,they were allowed to mix thoroughly before initiating mea-surements of their size distribution to establish a baseline.The evolution of aerosol particle sizes within the chamber was subse-quently tracked over time. Results and discussion The process of solving the aerosol transport equation using the discrete zone method is described in the paper.The effects of various factors,including heat transfer tube surface area,temperature gradient between the heat transfer tube wall and surrounding atmosphere,and non-uniform aerosoldistribution within the containment,on aerosol removal were studied.The results showed that:1)the calculated results of the theoretical calculation model in the paper matched well with experimental results,indicating its applicability for analyzing aerosol deposition processes.2)Increasing PCS heat transfer tube surface area and the temperature gradient near the tube wall could both enhance aerosol removal.Therefore,increasing the sur-face area of heat transfer tubes can be consideredin PCS design to optimize the source term.3)When evaluating the enhanced effect of PCS on aerosol removal,non-uniform aerosoldistribution within the containment should be considered,as results based on uniformity assumptions are not conservative.4)In the scaled-down containment model of the HPR1000 studied in the paper,PCS heat transfer tubes increased aerosol deposition efficiency by approximately 12％. Conclusion The following conclusions are drawn from the analysis:1)The developed theoretical model can be used for studying aerosol deposition processes.2)Increasing the surface area of the PCS heat transfer tubes and the temperature gradient near these tubes greatly enhance aerosol removal.3)When evaluating the enhanced effects of PCS heat transfer tubes on aerosol removal within the containment,the non-uniformity of aerosol distribution within the containment must be considered,as evalua-tions based on uniformity assumptions are not conservative.4)PCS heat transfer tubes can significantly enhance aerosol removal within the containment.