Experimental Study on Atomization Characteristic of Liquid Sodium in Sodium-cooled Fast Reactor

Abstract

Liquid sodium leaks and sodium fire accidents are common occurrences during the operation of sodium-cooled fast reactors and pose key and challenging issues in their development. Of the different forms of sodium fire, spray sodium fire has the most severe consequences and is the primary threat to plant safety. The atomization characteristics of liquid sodium are a crucial factor affecting the spray sodium fire. Studying these characteristics through experimental research could provide essential data for simulating and evaluating the safety of spray sodium fires. In this paper, an experimental visualization device that takes into consideration the material characteristics of liquid sodium was designed and constructed. In the experiments, the liquid sodium with varying masses (20-150 g) and temperatures (200-400℃) was injected from nozzles of different shapes (round, oval, sharp crack, rough crack) at different heights (55-85 cm) using high-pressure nitrogen (0.1-0.5 MPa), generating sodium liquid sprays. The experimental phenomenon was noted and recorded. Finally, the sodium spray was collected within a cooling tank filled with liquid paraffin, which caused liquid droplets to solidify into solid sodium particles. The size distributions of the liquid sodium droplets in the spray field were inferred by measuring those of solid sodium particles. The study analyzed the effects of injection pressure, initial sodium mass and temperature, leakage height, and leakage boundary shape on the liquid sodium spray characteristics. It is found that the process of liquid sodium spray can be divided into three stages:the column flow stage, the transition stage and the atomization stage. As the stages develop, the liquid sodium spray angle will progressively rise, reaching its peak during the atomization stage. The raising of leakage height and injection pressure causes increased flow rate of liquid sodium resulting in intensified air disturbance for more atomized sodium flow, leading to a decrease in mass intermediate diameter of the sodium spray. The atomization characteristics of liquid sodium are greatly influenced by the leakage boundary, and the mass intermediate diameter of the spray decreases approximately linearly with the increase of the shape factor of the leakage boundary. Increasing the initial temperature of liquid sodium may lead to a reduction in its surface tension and viscosity, potentially promoting sodium flow atomization. However, such changes are likely to be negligible, thereby limiting the impact of the initial temperature on the atomization characteristics within experimental conditions. The rise in sodium mass would result in an elevation of the liquid level within the crucible, thereby reducing the impact of high-pressure gas on the leakage end in the proximity of the nozzle. Consequently, the intermediate mass diameter of the spray will increase with the initial sodium mass. This research can provide fundamental experimental data for the simulation and safety assessment of spray fires of liquid sodium and can provide technical references for sodium fire prevention and control measures.

Keywords

• liquid sodium
• atomization characteristic
• particle size distribution
• leakage boundary
• spray angle