| The molten pool formed by core melting will directly threaten the integrity of the pressure vessel.In order to better achieve the nuclear safety goal of containing radioactive materials without leakage,it is necessary to conduct a detailed study on the molten pool and its internal melts,build a molten pool model and analyze the behavior of melts.Moving particle semi-implicit(MPS)method plays a very important role in computational fluid dynamics.In the process of calculating particle motion parameters,this method only needs to set the initial structure of the model,and does not need to set the topological relationship between particles.Therefore,MPS method has strong flexibility in simulating severe accidents and other complex conditions with large deformation.In the field of nuclear safety research,because the real experimental conditions are more stringent,the research of numerical simulation method and the development of related calculation program can not be ignored.MPS method was first proposed in 1996 to calculate the motion of incompressible fluid.Subsequently,many scholars at home and abroad have used this method to carry out academic research.In the field of calculation and analysis of nuclear power severe accidents,researchers have improved the initial MPS method to study the melting behavior of fuel rods,the eutectic reaction of lead and tin,the jet in the core,the delamination and solidification of melts,the interaction between melts and concrete,and the coupling calculation of particle method and grid method.MPS method has the advantages of direct calculation of particle motion and clear interface,so there is still a lot of research space in the flow and heat transfer analysis of molten pool.In this paper,the traditional MPS method is improved by adding the calculation part of heat transfer between particles and improving the MPS calculation program.Firstly,the steady-state heat conduction model of MPS heat transfer program is compared and verified by Fourier heat conduction law.It is found that the error between the calculated value and the theoretical value of MPS model is less than 1.5%under the steady-state condition,which verifies the feasibility of the calculation program.The practicability of the program is verified.Secondly,the natural convection model of square cavity with the same size and the same boundary condition is established by MPS program and fluent software.The temperature distribution of the two models at the same position at different times is compared and analyzed.The feasibility of MPS heat transfer program is proved again.Finally,the MPS program is used to establish the assumed initial conditions to simulate the process of high-temperature melt falling from the lower core support plate to the low-temperature melt in the lower head.The sensitivity of MPS method to the geometry of boundary conditions is analyzed by the shape of the molten pool model.The different behaviors of high-temperature melt falling from the left,middle and right positions of the support plate are discussed,The heat transfer and flow behaviors of high-temperature and low-temperature melts were obtained,which verified the feasibility of the improved MPS program for the simulation of flow and heat transfer behavior of molten pool.In this paper,the feasibility of MPS heat transfer model in steady state is verified by Fourier’s law of heat conduction,and the feasibility of natural convection model in square cavity of MPS heat transfer program is verified by fluent modeling.The behavior of molten material falling into the lower head is simulated by assuming initial conditions,and the flow and temperature distribution of molten material in the molten pool are analyzed,It is found that the simulation results are in good agreement with the expectation,which provides support for the numerical simulation of the flow and heat transfer problems related to molten materials in the reactor molten pool by MPS method. |
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