Ultrasonic Doppler Velocimetry (UDV) for Cold Shock Transients in a Scaled Liquid Metal Cooled Reactor Plenum

Abstract Liquid metal reactors experiencing low convective flux face a handful of issues that may deteriorate reactor safety. These long-standing issues, such as thermal stratification or thermal striping, can negatively impact the thermal behavior, mechanical systems, and neutronics of the nuclear reactor. To overcome these issues, safety analysis codes can be established. However, high-quality, validation grade experimental data are required for the development of such computational models, yet, such high-quality data are limited for low Prandtl number fluids such as liquid metals. To provide validation grade data for liquid metal, researchers at Purdue University have constructed the Gallium Thermal-hydraulic Experiment (GaTE). The GaTE is an experimental facility designed to study liquid metal cooled reactor transient conditions within a 1/20th scale model of the Advanced Burner Test Reactor (ABTR) outlet plenum. Gallium serves as a surrogate for sodium in the facility as the metal also exhibits a low Prandtl number in liquid form. Additionally, gallium is not cost prohibitive, nontoxic, and non-reactive with air and water, unlike sodium. To produce the desired transient conditions within the scaled plenum, the GaTE is capable of controlling the plenum inlet jet velocity and pool temperature as well as the system circulation. Control of the flow throughout the system is permissible through use of a moving magnet pump. An electromagnetic flow meter (EMFM) is employed to provide flow rate feedback data. The temperature of the gallium entering the plenum is regulated via a heat exchanger utilizing hot oil on the secondary side. Similarly, the fluid exiting the plenum passes through a heat exchanger using cool water on the secondary to reduce the temperature of the liquid metal. Thermocouples monitor the temperature of the gallium throughout the loop. A fiber optic distributed temperature sensing system is positioned within the plenum to provide temperature measurements of the liquid metal pool. Previously, the GaTE has been used to examine thermal stratification in a scaled liquid metal cooled reactor plenum based on flux Richardson number (Rif). These tests utilized the distributed temperature sensing system to characterize thermal stratification and the fluctuations associated with the stratification thermocline based on the proximity to the critical Rif. To relate the flux parameters to global parameters, flow velocity data within the plenum must be collected in addition to the temperature data. Ultrasonic Doppler velocimetry (UDV) is employed to obtain the desired data under cold shock transients in the scaled liquid metal cooled reactor plenum.