Research Of The Plume Diffusion With Nuclear Island Radioactive Waste Gas In The Nuclear Power Plant’s Cooling Towers

Actively the development of nuclear power plant, large natural draft coolingtower will be more and more. The nuclear island will be released radioactive wastegas during normal operation, the prediction of the behavior of these wastegas diffusion is the important work of the nuclear power plant environmental impactassessment. Hot and humid steam come from large natural draft cooling tower withthe rising momentum in the role of the horizontal environmental wind will form aplume; the plume will change the aerodynamic field on the cooling tower downstream.If the radioactive waste gas of nuclear island is located in this region, the spread ofradioactive waste gas will be affect by the plume.Nuclear radioactive waste gas is general discharge by the ventilation system(DVN) of the nuclear island auxiliary building to the atmosphere by altitude chimney.Under the influence of the ambient wind, the leeward side of large cooling tower in awide range of space will make up a very complex three-dimensional aerodynamicfield, the traditional analytical methods (such as Gaussian plume model) will not beable to accurately predict the plume and the diffusion behavior of radioactive wastegas from the nuclear island. In order to predict the plume diffusion of cooling towerand the Proliferation of nuclear island radioactive waste gas in the environmentalwind and building’s affect, this research proposes using3D CFD(Computational FluidDynamics) numerical simulation method, relying on FLUENT powerful softwarecomplexity of boundary treatment, the mesh generation capacity, turbulence modeland numerical simulation of heat and mass transfer model to carry out:1) Numerical simulation of the cooling tower plume.The results show that the different environments of wind speed on plume risebending have a larger impact; turbulent Schmidt number on the plume of the humidityfield has a greater impact. The plume near field increase the cooling tower airdiffusion capacity, Sc lower, the ability to spread will be stronger, which willpromote the spread of radioactive waste gas from nuclear island.2) Steady-state calculation of the spread of radioactive waste gas of the cooling tower plume.The results show that cooling tower plume velocity has a greater impact on therelease of radioactive waste gas from nuclear island with a altitude chimney, Theshape of the cooling tower plume depends on the intensity contrast of thetransverse to the airflow speed and the vertical upward flow of the cooling tower3) Non-steady-state calculation of the spread of radioactive waste gas of the coolingtower plume.The results show that in low wind speed, the spread of radioactive wastegas plume influence; Environmental wind in high wind speed has a direct effect ofradioactive waste gas diffuserThe plume of cooling tower and proliferation of radioactive waste gas for thenuclear island is a typical jet flows, this research focuses on the environmental windcross-flow velocity, temperature, and cooling tower exit velocity, temperature spreadof radioactive waste gas on the downstream of nuclear island, as well as the affect ofturbulent diffusion parameters on the calculated result. The establishment ofnon-steady-state radioactive waste gas decay mode can be used for normal operatingconditions or accident operating conditions of the nuclear island radioactive waste gasand radio nuclides (e.g. I-131, etc.) of the prediction calculation, calculated by theabove results, we can conclude as follows:In general, the cooling tower wake has more impact than the cooling tower plumeto the radioactive of nuclear island;When high exhaust outlet location of the nuclear island, the aerodynamicfield formed by the cooling tower plume directly affect the diffusion trajectoryof the radioactive waste gas of nuclear island;The cooling tower plume increases the diffusion field of scalar diffusioncoefficient, which is conducive to the spread of the waste gas;With no winds, the plume vertical ascent, had no effect on the proliferation ofradioactive waste gas of nuclear island;The turbulent Schmidt number on the ambient atmospheric flow field plumedistribution has a greater impact; Non-steady-state calculation with steady-state calculation results are consistent,however, due to the non-steady-state calculation taking into account theradioactive decay, concerned about the spread of radioactive waste gas dynamicprocesses (especially nuclear power accident conditions), the use ofnon-steady-state model can predict the changes in the scope of the plume and thespread of nuclear radioactive waste gas.