Visualization of nuclear thermal-hydraulics

The VISUALIZATION is the strong tool to understand the complicated two-phase flows, including boiling. Many problems on the Nuclear Thermal-hydraulics are multi-disciplinary problems, e.g., Interaction between Material and Fluid, Interaction between Radiation and Heat Transfer, and so on. For these complex interdisciplinary problems, visualization studies help to investigate the mechanisms. In this decade, the technology of the high-speed camera has been progressed drastically. One Mega-pixel image can be captured with a sampling rate of 7000 Hz upto several seconds continuously. The complicated two-phase phenomenon can be clearly visualized using these tools. The boiling phenomenon under the irradiation condition has different characteristics to that under the non-irradiation conditions. The phenomenon was called as the RISA, Radiation Induced Surface Activation. With the gamma-ray irradiation to oxidized material surface, many interesting phenomena have been reported including, boiling enhancement, corrosion protection, and so on. The visualization study with high-speed camera can reveal the mechanism of the nucleate boiling degradations. The RISA is the interdisciplinary problems, i.e., Interface area of Radiation, Material and Thermal-hydraulics. Other applications of the high-speed camera on the interdisciplinary thermal-hydraulic problems will be discussed. Also, the future researches using the visualization technology will be reviewed. (author)