Numerical Study on the Turbulence Penetration and Thermal Stratification Characteristics of CFETR Divertor PHTS Pressurizer Surge Line

The thermal stress and thermal fatigue caused by the turbulence penetration and thermal stratification could cause damage to the pressurizer surge line, which will further endanger the safe operation of the divertor primary heat transfer system (PHTS) in the China Fusion Engineering Test Reactor (CFETR). In this article, the new criteria for determining the length of turbulence penetration and thermal stratification level are proposed to predict turbulence penetration and thermal stratification behaviors. The velocity W (velocity component in the
$z$
-axis direction) and temperature gradient can be used as criteria to judge penetration length. Meanwhile, the stratification intensity factor is considered as a criterion of the thermal stratification level. According to the computational fluid dynamics (CFD) simulation results and the criteria, it is observed that the swirling penetration phenomenon occurs in the turbulence penetration region, and the penetration length is 1.35 m. It is also found that the most severe thermal stratification occurred in this position with a stratification intensity factor of 0.67. This work lays a foundation for the surge line analysis in the field of fusion reactor such as CFETR and provides the reference for evaluating the thermal state of the surge line in the future.