Numerical simulation of airflow characteristics during the loss of vacuum accident of CFETR

During a loss of vacuum accident (LOVA) of China Fusion Engineering Test Reactor (CFETR), the high velocity airflow will result in the migration, re-suspension even explosion of theradioactive dust deposited in the vacuum vessel (VV) during plasma burning. In addition, large amounts of hydrogen may be produced from the exothermic reaction between tungsten and water/steam. In order to minimize the risk of explosion and the leakage of radioactivity, the airflow characteristics must be well studied at the first step. In this paper,a break due to a failed component is assumed to take place at the equatorial port. The numerical simulation has been performed by using ANSYS CFX code with a simplified VV model of CFETR. The airflow field during LOVA has been studied in detail under different initial pressure and first wall (FW) temperature. The results show that the FW temperature significantly affects the pressurization process. Besides, the friction velocity is also greatly affected by the FW temperature and initial pressure. From the 3D airflow distribution, the velocity near the lower part of torus can reach up to 87.4 m/s. This study provides indispensable basis for the research about dust resuspension, migration, dust/hydrogen explosion and the radiological safety of CFETR.