| When a break accident occurs in a nuclear power plant,a large number of radioactive substances will be released from the break.If the containment fails at the same time,a large number of radioactive fluids and radioactive aerosols will be released into the environment,causing serious harm to the environment and surrounding residents.The occurrence of a break accident will inevitably lead to the investment of the spray system.The spray system will lower the temperature and pressure inside the containment,thereby ensuring the integrity of the containment and reducing the consequences of the accident.Therefore,by analyzing the diffusion characteristics of fluid and aerosol particles in containment and the influence of spray system input on the diffusion characteristics of fluid and aerosol particles,suggestions can be provided for the layout of spray system and the radioactive consequences of the accident can be predicted.In this paper,the Fluent module in ANSYS software is used to establish a calculation model with a typical passive reactor as the research object,and different sizes and directions of the break are selected for calculation and analysis.Based on the simulation of the transient process of the break accident,this paper focuses on the influence of different size and direction of the break on the flow and distribution of the fluid and aerosol particles in the containment,and analyzes the influence of the spray system on the flow and distribution of the fluid and aerosol.The calculation results show that:After the break accident,the fluid flow has a strong directivity,and two similar vortices will be formed near the containment wall directly opposite the break.Different components of the multicomponent mixture released from the break in a short period of time are distributed similarly in the containment.Under the action of buoyancy,the flow released at the break will flow up to the space;Weak concentration stratification occurs in the containment space.The position and size of the two vortices generated by the secondary flow in the containment are slightly different under different break size accidents.The change of the direction of the break will change the flow directivity of the fluid in the containment space.The farther the break is from the opposite containment wall,the more uniform the fluid radioactivity distribution in space.The flow of aerosol in the containment is similar to that of fluid,and most of aerosol accumulate in the space below the break.Near the break,the aerosol is mainly affected by Saffman force and drag force.Near the wall,the aerosol is mainly affected by drag force,thermophoretic force and Saffman force.With the increase of the size of the break,the distribution of the radioactive activity of aerosol in the containment becomes more uneven.The farther the break is from the opposite containment wall,the more uniform the fluid radioactivity distribution in space.After the spray system is started,both the pressure in the containment and the mass share of soluble gas have decreased significantly,the velocity of the fluid in the containment has decreased slightly,the size of the secondary flow vortex has increased and the shape has changed;for aerosol,The activation of the spray system will significantly reduce the Saffman force and drag force on the aerosol in the containment,the size of the secondary flow vortex will also increase,and the capture rate of aerosol will increase significantly.The spray system flow is set as the spray flow near the wall and center is larger,and the flow at other positions is lower. |
