Session: 07-07: Experiments and Analyses - VI

Paper Number: 136650

136650 - Experimental Study on Bubble Rising Behavior in Low-Temperature Molten Lbe With Ultrasonic Doppler Velocimetry 

Abstract: 

Lead-based Fast Reactor (LFR) is regarded as one of the six most promising generation-IV nuclear reactor systems due to its excellent performance in neutronics, thermal-hydraulics and inherent safety. Lead-based alloys (most commonly pure lead and Lead-Bismuth Eutectic: LBE) as the primary coolant candidates possess several advantages in properties such as low neutron capture cross section, low saturation vapor pressure, high boiling point, high thermal conductivity and chemical inertness with water and air. During a Steam Generator Tube Rupture (SGTR) accident in Lead-bismuth cooled Fast Reactor (LFR), the highly-pressurized water in secondary loop will discharge into the low-pressure high-temperature molten Lead-Bismuth Eutectic (LBE) in the primary reactor vessel, leading to sudden water vaporization, rapid pressurization, and even potential threat to in-vessel structure. When the generated steam bubbles enter the reactor core, it would further cause reactivity fluctuation and even deteriorate the heat transfer. Hence, fully understanding the behavior of bubbles in molten LBE is very important for the safety design of LFR. The bubble rising behavior in liquid metals are difficult to observe optically since the liquid metal is opaque. While Ultrasonic Doppler Velocimetry (UDV) can effectively overcome the observation problems and can be used to measure bubble rising velocity accurately. In this study, two apparatuses were designed and built. The first apparatus is a molten LBE-bubble two-phase flow apparatus, which is used for the measurement of the terminal velocities of rising bubbles in molten LBE. The main part of the apparatus is a stainless-steel cylindrical container with an inner diameter of 100 mm and an inner height of 250 mm. The nozzle is an integrated high-temperature resistant structure deployed at the bottom of the f apparatus, which is connected to a stainless-steel tube. The other end of the tube is connected to a high-precision mass flow controller. Intermittent electromagnetic heating was used to heat the LBE and maintain the temperature of the molten LBE at about 155°C during the experiment. The second apparatus is used to verify the reasonability of UDV measurement, where a single bubble is released in transparent liquid and the bubble rising velocity is measured simultaneously by high-speed camera and UDV. Then, the terminal velocity of a single nitrogen bubble with different diameters in liquid LBE was measured. The following conclusions are obtained: (1)   UDV measurement is accurate for the rising velocity of bubbles with diameters of 3-8mm in several liquids. And the small offset of the bubble in the horizontal direction from the axis of the UDV probe does not affect the velocity measurement results. (2) The trend of bubble rising terminal velocity is consistant with the velocity predicted by Mendelson and also satisfies the predicted effect of Jamialahmadi's empirical formula. (3)   The bubble rising terminal velocity in molten LBE is in the range of 200mm/s-230m/s.

Presenting Author: Hui Cheng Harbin Engineering University

Presenting Author Biography: Dr. Hui Cheng got his B.S. degree from Sun Yat-Sen University and PhD degree from City University of Hong Kong. He is currently an associate professor in the college of nuclear science and technology of Harbin Engineering University. His research interests include thermal-hydraulics and safety of Gen IV nuclear reactor system, nuclear severe accidents analysis and advanced numerical modeling method.

Authors:

Hui Cheng Harbin Engineering University
Jiayuan Li Harbin Engineering University
Minyang Gui Harbin Engineering University
Songbai Cheng Harbin Engineering University
Zhaolong Li Sun Yat-Sen University