Numerical Simulation Of Flow And Heat Transfer Characteristics Of The Molten Pool Oxidation Layer Based On Experiment

When a serious accident happened at the nuclear power plant, the fuel elements inside the pressure vessel and the internal components of reactor melt. The molten material drops into the bottom head of the pressure vessel, and forms into the molten pool structure. As the oxide layer is the heat source of the whole molten pool, its internal flow and heat transfer characteristics determine the heat flux of the polar angle and metal layer. By researching the oxide layer, it could reduce the uncertainty in the process of pressure vessel heat flux calculation and it is of great significance for the improvement of the reactor power.This topic chooses a CFD software and suitable calculation model, and conducts a numerical simulation study, using the molten pool of oxide layer experiments conducted as the geometric prototype. By careful comparison, this paper chooses the Fluent as the simulation software, and selects the large eddy models (LES) and solidification and melting models as the simulation models. Through the study of the numerical simulation of nitrate experiment carried out, it validates the correctness of the selected calculation model.On the basis of verifying the applicability of the calculation model, the boundary condition is fixed temperature boundary 1178K, to numerical simulate the two phase mixing region and the melting zone in the molten pool of the mixed oxide of calcium oxide. Then the simulation results are analyzed from three aspects, including the flow field distribution, the temperature field distribution and the heat flux. By the result of the two-phase mixing zone and internal simulation, it can be known that the oxidation flows from the bottom to the upper by the internal heat source, and forms eddy in the upper zone, then flow to the wall in the function of eddy and down along the hemisphere wall. The temperature in the bottom is stratification, but it is broken by the eddy in the upper zone. The heat flux of the hemisphere wall is mainly constant at the small angle (blow 30°) , once exceeding 30° the heat flux increased rapidly. It also can get the corresponding relationship between Nu of molten pool and Ra under the molten pool.On the basis of the analysis of the flow and heat transfer characteristics in the inner region of the oxide layer, through the shell, the heating power, the upper cooling condition and the molten pool height four aspects, the numerical simulation of oxide layer melt pool is conducted. The temperature boundary conditions are obtained by the numerical simulation of the hemisphere passage model and the upper cooling passage. The result indicates thickness of shell decreases with polar angle increases. That the existence of shell can increases the heat flux in low polar angle, and it could reduce the pool of transfer heat flow upwards. Through analysis of the simulation results of different heat source in power pool, the formula of the heat transfer can be got. When the molten pool height is lower than the molten pool radius,the upward heat transfer formula downward shall not apply. For the different power of the pool, the relation of the different angle heat flux and the wall average heat flux can be expressed by the same empirical formula. For the different height of molten pool, only in polar angle more than half maximum polar angle, the formula apply.