Numerical Simulation of Structure Phase Change under High Heat Flux Condition Coupled with Nuclear System Analysis Code

high heat flux transient analysis;solid phase change heat transfer;mushy zone;mesh adaptation technique;blanket;MARS;FLUENT;622.33

원자핵공학 ;

University:서울대학교 대학원

关键词: high heat flux transient analysis;    solid phase change heat transfer;    mushy zone;    mesh adaptation technique;    blanket;    MARS;    FLUENT;    622.33;   

Others  :  http://s-space.snu.ac.kr/bitstream/10371/161033/1/000000157386.pdf

美国|英语

来源: Seoul National University Open Repository

【 摘 要 】

Under the high heat flux transient conditions that can occur in a nuclear system, the thermal and structural integrity of several structures can be worsened. In particular, because of the high temperature plasma and its instabilities, high heat flux conditions can easily apply to the plasma facing components in a nuclear fusion reactor. It causes the phase change of the material, such as melting and evaporation of structure. Furthermore, the temperature increase due to the applied high heat flux may cause a burnout situation in the cooling channel, so that the heat transfer efficiency can be drastically reduced. The phase change of structure affects the heat transfer phenomenon in both solid material and cooling system connected to it. Thus, the thermal-hydraulic analysis for the phase change behavior of the structure and the two-phase flow heat transfer in the cooling system are necessary for the safety analysis. Studies on the safety so far, however, have been limited to segregated calculations for a structure phase change or a system analysis. Therefore, the main objective of this study is to simulate the phase change in structures by a code coupling with a nuclear system thermal-hydraulic analysis code.First, for the simulation of heat transfer including the phase change through the wall, the one-dimensional phase change calculation module with evaporation and melting model was developed. The limitations due to the imaginary concept of mushy zone used in the effective heat capacity method, the melting model, were identified. To improve it, a mesh adaptation technique using a monitoring function was adopted in the module. The technique reconstructs the mesh at each time step, according to the temperature profile in the structural material. As a result, the calculation efficiency and utilization of the calculation module were improved. With the improvements in the numerical module, calculation time was reduced by 5 times and it facilitates a more realistic melting simulation. After the improvement, the one-dimensional phase change simulation module was coupled with MARS-KS using its DLL version. Its purpose was to analyze the cooling system with the coupled code between the solid phase change and thermal-hydraulic behavior.Afterwards, the phase change simulation was conducted for the first wall of blanket, one of the plasma facing structures in a nuclear fusion demonstration reactor, K-DEMO. The VDE scenario caused by plasma instability was analyzed in 5 cases classified by the heat flux size and the transient duration time. For these cases, evaporation and melting thickness, penetration depth, and the duration of phase change time were compared with each other.In addition, the two-dimensional melting calculation was conducted using ANSYS-FLUENT to identify the natural convection effects that could occur inside of the melted layer. As a result, the internal flow of the structure made a slight shape change of the solid–melt interface. The coupled calculation between ANSYS-FLUENT and MARS-KS was progressed as well. CORBA was used as a program-to-program control method and both socket communication and file input/output method were used for code coupling. According to the established code coupling methodology, the transient phenomenon under high heat flux condition on the blanket was simulated and the occurrence of film boiling in the coolant channel was observed. Following the transition to the film boiling, it was also identified that reduced cooling performance and increased melting duration time.