Simulation Study On Diffusion Of Airborne Radioactive Contaminants In Nulear Accident

Nowadays,Nuclear power has been and will continue to be an important energy source which could meet increasing electricity demand for electricity while protecting air quality.Although various nuclear facilities have strict management systems and defense in-depth measures,but cannot completely exclude the possibility of accident.When major radioactive accident occurs in a nuclear facility,it will have a serious impact on the surrounding land and marine environment within a short period of time.Therefore,the consequences assessment and analysis of nuclear accident is particularly important,because it is necessary to take emergency protective measures in advance to reduce or even avoid possible radiation exposure.The pollutants generated by the nuclear accident can be divided into two parts:gaseous radionuclide and radioactive aerosols.There may be hundreds of fission products and activating products,and the main nuclides released into the environment are those with high fission products,medium half-life and the corresponding those radioactive material properties of the gaseous or volatile substances.Within these gaseous radionuclide,we mainly monitor the concentration distribution of ¹³¹I,⁸⁵Kr and ¹³⁷Cs.And the aerosol which particle size of 0.01μm to 100μm is formed by the capture of atmospheric suspended matter.Based on geographic information system,the output exposure dose or distribution diagram of concentration and data table are respectively output for ¹³¹I,⁸⁵Kr,¹³⁷Cs and radioactive aerosol,and then output concentration distribution diagram respectively as the decision-making reference.In this paper,the Lagrange Smoke Puff model is used to simulate the gaseous radionuclide.The model has lower standards for the computer resource,less demanding for the operators.Besides,the concentration field at any time can be distinguished through the model.Tt is suitable to simulation the movement of amounts of particles according to random waking-smoke model,on account of the randomness of particle diffusion in the spreading of radioactive aerosol.The model features the definite structure and simple in calculation.Because above two models rely on local wind field in a certain extent,this paper will construct small-size part wind field by using CFD fluid calculation software named‘star-ccm‘combining with interpolation method.We choose maritime nuclear facilities to conduct simulation test and construct the wind field according to the local terrain conditions and meteorological conditions.In order to achieve the prediction of nuclear accident concentration in a specific area or nuclear facilities,we base on wind fields and the local weather conditions at the time to select the parameters such as atmospheric stability and other parameters.The simulation results show that the diffusion of radioactive material at a small scale increases with the increase of the downwind distance,and the diffusion of radioactive concentration on the axis will get larger.The distribution of radioactive concentrations per hour is consistent with the theoretical situation.The wind field model the Lagrange Smoke Puff model and the random walk-the smoke group model used in this paper can simulate the diffusion process of radioactive material under nuclear accident very well.