Temperature and High Resolution Velocity Measurements of Natural Circulation Flow in a Scaled Water Reactor Cavity Cooling System (WRCCS)

In the U.S., the helium-cooled VHTR has become the centerpiece of DOE NGNP program. Among the VHTR design’s many technological innovations is a safety system called reactor cavity cooling system (RCCS). The RCCS provides means entirely external to the vessel to reject decay heat to the environment without the need for pumps, diesel generator, or human intervention. Besides keeping structures under designed temperatures during normal operations; the RCCS can take advantage of the high temperature in the vessel to passively remove the heat from the reactor cavity and maintain the reactor system under safe conditions throughout the transient in case of a loss of forced coolant accident. Computational Fluid Dynamics (CFD) tools may provide a mean to analyze the behavior of the system, and conduct proper sensitivity analysis and design optimization. Industrial CFD codes have been employed for this scope, but there is still a lack of natural circulation experimental data to confirm the capability of these codes to faithfully simulate such phenomena. The present study investigated temperature and flow distribution in the TAMU’s 1/23 scaled facility under steady-state conditions. Temperature distributions is studied using time-averaged temperatures. Flow distribution is studied using different decompositions including Reynolds decomposition, Galilean decomposition, and proper orthogonal decomposition (POD). Lastly, flow frequency is studied using Welch approximation together with Tukey’s fence. Results found volumetric flow rate to be low for the system. Within the range of Re analyzed, temperature and flow is symmetric at the lower Re, and asymmetric at the higher Re. Flow’s dominant frequencies are found to be 0, 20, and 40 Hz