The Research Of Offshore Liquid Radioactive Material Diffusion Model

With Japan’s Fukushima nuclear accident happening, the leaked liquid radioactive material makes the radioactive content near to the accident address rising sharply, impacting the environment around and the safety of Marine biodiversity.Therefore, the transport diffusion mechanism of radioactive material in water has taken high attention by outside world. Through numerical simulation after the nuclear accident rapidly and accurately figuring out time and space distribution features of radioactive pollutants in waters near the accident has become an important research subject.This article will analysis the main source offshore and various types from the main reactors in our country’s nuclear power plant. To systematically describe the Lagrange Random Walk Theory which simulate the spread of radioactive material transport. To give the method to get the turbulent diffusion coefficient and obtain the three dimensional ocean flow field information which are needed in the process of numerical simulation. By constructing an ideal instantaneous point source releasing model with numerical simulation,it proves that the introduction of Kernel Function Method instead of the traditional method of particle concentration calculation in Lagrangian random walk model concentration calculation part is feasible. Using the numerical method to simulate the different situations changing with the total number of particles and pollutants convection diffusion time finally to give the optimal values of the frequency width correction factor under corresponding conditions.Following are the conclusion from this paper.1) Determine the main radionuclides in our numerical simulation to the radioactive material transport diffusion offshore are Cs-137,I-131, Sr-90and Sb-124.2) Give the turbulent diffusion coefficient values of radioactive material transport diffusion by the Lagrange Random Walk theory.a) For horizontal turbulent diffusion coefficient, when the horizontal velocity is unkown, the two horizontal turbulent diffusion coefficient values both are6.318×10-7t1.34; When the horizontal velocity is known, the turbulent diffusion coefficient values both are0.0025U2t.The unit of the above two cases for both horizontal turbulent diffusion coefficient is m2s-1.b) For vertical turbulent diffusion coefficient, its value can be divided into two categories:one is getting a certain value in the whole vertical direction: Kv=ξCv(?)u2+v2h, the ξ ranging from0.1to0.5, the Cv is0.0025; Another is that the vertical turbulent diffusion coefficient changes with the height of the vertical direction:Kv In both two cases, the unit of the vertical turbulent diffusion coefficient is m2s-1.3) Determine in the part of the particles random walk model in the Concentration Calculation using wide frequency Epanechnikov Kernel Function method instead of the traditional method to calculate pollutant concentration of particles can effectively overcome the fluctuation of the contamination concentration increased with the simulated particles convection diffusion distance during the concentration Calculation.4) Using wide frequency Epanechnikov Kernel Function method to simulate the different situations changing with simulated particles and pollutants convection diffusion time, the results come out that the number of simulated particles is106and the width frequency correction factor is0.45.Take the calculated contamination concentration attribution. the maximum decrease of Contamination Concentration and time needed into consideration, the results are the optimal.