Characteristics of Helium Gas with High Temperature and High Pressure Flowing through a 90-Degree Elbow

There exists a certain 90° elbow structures in the helium circulation of HTGR-10. In terms of energy-saving and design simplification of reactor’s primary loop, 90° elbow can be used to measure the helium flow and the content of water vapor, both of which are significant in an accident. It is necessary to make an in-depth research of the flow characteristics of helium flowing 90° elbow. Simulation results indicate that fluid’s motion in the elbow is under the control of the centrifugal forces. Static pressure near the extrados is higher than that near the intrados. Boundary layer separation occurs at the latter half intrados of the elbow. The vortex emerges during the separation process and increases the energy dissipation. Velocity in the near-intrados region is higher than that in the near-extrados region, which is opposite to the pressure distribution trend. Under the action of the centrifugal forces, the secondary flow emerges in the latter half of the elbow and complicates the flow field by generating two vortexes which rotate in a different direction. 1. Introduction High temperature gas-cooled reactor (HTGR), which is developed from gas-cooled reactor and advanced gas-cooled reactor, is an advanced type of reactor in nuclear power reactors. High temperature gas-cooled reactor has a lot of advantages over traditional rectors, such as higher inherent safety, better economy, and higher power generation efficiency, and also the process heat generated by HTGR can be applied in nuclear hydrogen production [1] and some other fields. The HTGR has the potential to become one of the advanced reactors which will be upgraded preferentially [2]. The primary circuit of high temperature gas-cooled reactor works with helium as the cooling medium. The helium flow through the gap between the spherical fuel elements takes away the heat generated by the fission of U-235 and then transfers the heat to the steam generator. Then, the working fluid of the secondary circuit absorbs the heat energy and moves the steam turbine work. The system figure of a 10-MW HTGR is shown in Figure 1. Figure 1: The primary circuit of the HTGR-10. The integrality and resistance characteristic of the primary circuit has a significant influence on the safety and economy of HTGR. The accurate measurement of the helium’s flow and pressure is the precondition for safe and stable operation of the HTGR, especially in an accident. At present, these critical parameters are measured by additional local resistance component. But additional local resistance components engender some serious harm that