Thermal Stress Analysis During Divertor Baking Process Based On 1D And 3D Coupled Model

Divertor is an important component within the vacuum chamber of a Tokamak reactor, which is used to absorb the plasma outside the magnetic flow interface to avoid the ablation of first wall, also, it can remove the helium ash from vacuum chamber. Before the running of Tokamak, divertor need to be baked to remove moisture and impurities attached to the surface. However, high thermal stress in the fixed structure of divertor targets can be produced during the baking process due to the temperature gradient. The main purpose of this thesis is to study the thermal stress of divertors during the baking process. By analyzing the thermal stress of EAST and ITER divertor under different baking rate, it shows the best baking rate of the two kinds of divertors that can decrease the thermal stress. By the way, in order to simplify the calculation process of flow within the pipeline, this thesis develops a model coupling one-dimensional flow and heat transfer calculation and three-dimensional heat transfer calculation. The coupling model is preliminarily used in the thermal stress analysis of Tokamak divertor. The main contents are listed as follows:(1)Development of a one-dimensional flow and heat transfer model and writing of the calculation program of one-dimensional model with Fortran language. This model can simplify the calculation process of flow and heat transfer within divertor pipeline.(2)Coupling of the one-dimensional flow and heat transfer model and Fluent three-dimensional heat transfer model by Scheme script. By comparing the results of the coupling model with Fluent software, it proves the accuracy of the coupling model.(3)Establishment of the simplified model of EAST divertor and analysis of the thermal stress of EAST divertor during the baking process by calculating the temperature and thermal tress distribution under different baking rate. The results show that there is a large correlation between thermal stress and temperature gradient. Thermal stress is greatly influenced by baking rate, and slowing down the baking rate can significantly reduce the thermal stress. When the baking rate is reduced to 0.001 K/s, the thermal stress can meet the strength requirements.(4)Establishment of the simplified model of ITER divertor, and analysis of the thermal stress of ITER divertor during the baking process by calculating the temperature and thermal tress distribution under different baking rate. The results show that strong constraint connection such as welding will cause excessive thermal stress during baking process, so ITER divertor needs weak constraint connection such as pin linking. When the target plate and bottom plate are connected by pins, the overall stress is much smaller than the welding. And the faster the baking rate, the bigger the maximum thermal stress. When the baking rate is reduced to 0.1 K/s, the influence of temperature gradient on the thermal stress is very small. In addition, the study also finds that a large shaping yield phenomenon of pure copper interlayer occurres in the baking process. It can reduce the thermal stress in the junction of tungsten monoblock and CuCrZr pipe, and the thermal stress of support structure also can be reduced at the same time.