Research On Simulation Of The Radionuclide Migration Using Lagrangian Particle Model

A lot of measures were taken to avoid nuclear accident happened in nuclear power station, but Three Mile Island accident, Chernobyl accident and Fukushima accident have shown that nuclear accident are inevitable. After the nuclear accident, the timely assessment of the severity of the accident, the accident prediction of radionuclide concentration distribution, etc., can provide emergency bases for government agencies to facilitate the use of appropriate methods to reduce harmful levels of accidents on the environment. Now, the international community usually use accident consequence assessment method to simulate the dispersion of radionuclides in the environment, through simulating the plume trajectory and diffusion law, estimate the radiation dose concentration finally.In this paper, after making research of the atmospheric evaluation models, the Lagrangian particle model was selected as a radionuclide migration model, and had intense research in follows:1) Wind field diagnostic method was used to analyze the monitor data, adjust the monitor data to whole area, and simulate the wind speed in different height with terrain following coordinate.2) The building downwash effect was considered, and OML model was used to solve the influence affected by the building.3) Considering the wet deposition caused by the rain or the snow, and parameterized principle was used to solver the wet deposition.4) The release rate is different in different time, so the decay equations are changed and the calculate result is much accurate.Finally, a Lagrangian particle simulation code SDUL was developed using Fortran 90 Language, SDUL atmopsheric dispersion model was used to simulate the air concentratin distribution of radionuclide 131Ⅰ during 10days after the accident. The simulation area is a 180km×180km region which center is located in the Fukushiam Daiichi nuclear power plant, and compared with aerial survey results; and Mito City was choosed as a monitor to test the accuracy of SDUL code. And the result showed that SDUL model can simulate the atmopsheric diffusion in case of nuclear accidents very well and provide more actural information for early emergency and consequence assessment as nuclear emergency dicision support system.