When a heat transfer tube wall in a steam generator of a sodium-cooled fast reactor fails, high-pressure steam leaks into low-pressure liquid sodium side. Then the chemical reaction between steam and liquid sodium causes the erosive and corrosive reaction jet, and the secondary failure of a neighboring heat transfer tube is expected. The objectives of the present experimental study are to understand the structure of an underexpanded impinging gas jet which is injected into liquid sodium and to grasp a relationship between the gas jet velocity and the erosion characteristics of liquid sodium droplets which are entrained into the gas jet.
In the present study, the structure of an underexpanded inert gas jet impinging on a single cylinder within liquid sodium was clarified using the visualization method, which has been constructed by the authors. Then the erosion tests were carried out at the most erosive geometry, which was confirmed by the visualization experiments.
From the visualization, the underexpanded impinging gas jet in liquid sodium could be classified into four regions: core region, droplet flow region, liquid film flow region, and separation region. The erosion phenomenon on the cylinder surface was observed only when the droplet flow region was impinged. In this region, the liquid droplet impingement type erosion was confirmed. The erosion rate, the ratio of the volume loss of specimens to the duration time, was correlated as the function of the gas jet velocity at the end of the external expansion region.