Research On Simulation Of Sodium Droplet Combustion Of Sodium Fire

Compared to the previous generations of reactors, the fourth generation reactor on economy,uranium resource utilization has greatly improved,and the sodium cooled fast reactor is a typical representative of the fourth generation reactor. However,when the liquid sodium leak from coolant systems, it can react violently with oxygen and pose a risk for the potentially dangerous consequences,it could cause a serious security problem to the safe operation of the nuclear reactors, and sodium droplet combustion is the basis of the sodium fire. So in this paper, the detailed study on simulation model of sodium droplet combustion of sodium fire.In this paper, combined with the simulation experience of other metal and non-metal droplet combustion,used the sodium droplet pre-combustion model and gas phase zone combustion model,the simulation model of sodium droplet combustion is completed. Chosen the FLUENT software to simulate the sodium droplet combustion, In order to verify the simulation model, based on sodium droplet combustion experiment, the simulation results and experimental results are compared,the simulation model has a high precision,and the prediction error is not more than 7 to 10%. Finally, based on the simulation model, the characteristics of sodium droplet combustion is analyzed, including heat of reaction,concentration distribution of species and so on. In addition, the factors affecting of sodium droplet combustion are studied, such as initial temperature, diameter, oxygen concentration and intensity of convection.According to the simulation results, sodium-oxygen reaction occurs on the surface of the droplet, and the high heat of reaction is produced at this position, when the initial temperature of 523K, oxygen concentration 12%, the maximum heat of reaction is 4.98W. Due to the occurs of reaction and the entry of oxidant, making the sodium vapor can't spread to far from sodium droplet surface, When sodium droplet combustion occurs, the highest temperature as the flame temperature of combustion zone. At the initial stage of sodium droplet combustion,because of the rate of evaporation is smaller, oxygen mass fraction is lower in the environment, chemical reaction is weaker, as time increase, the sodium-oxygen reaction become violent, it make the heat of reaction and reaction products to increase rapidly, due to the sodium peroxide breaks down into sodium oxide and oxygen at high temperature, so the mass fraction of sodium oxide is greater than the sodium peroxide. Oxygen mass fraction in combustion chamber is mainly determined by air inlet velocity, outlet exhaust rate and ability of react, mass fraction of sodium vapor is mainly determined by ability of reaction and rate of evaporation. By varying the oxygen concentration can change the mechanism of sodium droplet combustion, and the other factors affecting only can change the intensity of sodium droplet combustion, the corresponding value of factors affecting is upper, the sodium droplet combustion more intense, but with the increase of its value, the effect of factors affecting on the sodium droplet combustion is decreased.Combining with the characteristics of sodium spray fire, chosen the FLUENT software to preliminary simulate for the characteristics of sodium droplets in atomization field, under the different initial diameter (5-8mm), the DPM model track the sodium droplet diameter,Reynolds number and the distribution. The greater of the initial diameter, the sodium droplet diameter change rate is smaller,more concentrated sodium droplet position, the greater of the Reynolds number. The result for the study of sodium fire offer a certain theory basis.