Measurement of free-surface velocity of liquid lithium flow for IFMIF

Experiments on the high-speed liquid lithium flow with free surface were conducted using the lithium circulation loop at Osaka University for International Fusion Materials Irradiation Facility (IFMIF). The test section of the loop has a contraction nozzle which is 1/2.5 scale of IFMIF and provides a flat plane jet of 70 mm width and 10 mm thickness. In the present study, new surface velocity measurement was tested, to develop a diagnostics system in view of its application on IFMIF lithium target. The measurement is based on particle image velocimetry (PIV) technique. Patterns of surface waves generated on the flow are tracked using a pair of images with short time delay with using an algorithm called gray level difference accumulation, and a velocity field is attempted to be calculated by correlating the two images. As a result, the surface velocity field was successfully measured even very close to the nozzle exit. It is expected that the present velocity measurement method could be applied to the monitoring and diagnostics system of the IFMIF target.