Cavitation is a key engineering issue in various turbo-machinery applications. Also in an advanced loop-type sodium-cooled fast reactor (advanced SFR), vortex type cavitation has become an important issue to be cared from the viewpoint of the integrity of structural materials of the reactor. Therefore, a method to evaluate this type of cavitation needs to be established. In this paper, vortex cavitation behavior is studied using a 1/22-scale upper plenum water model of the advanced SFR. Vortex cavitation occurrences are quantitatively grasped through visualization measurements, including the transient behavior under various conditions of inlet velocity at the suction pipe, water temperature, and system pressure. In addition, the relationships between the local velocity around a vortex and vortex cavitation occurrences are investigated based on the results from the visualization and Particle Image Velocimetry measurements. The experimental results show the difficulty of evaluating vortex cavitation occurrences based on a macroscopic parameter, i.e. cavitation factor. In contrast, the results of vortex evaluation with local circulation give a good agreement with the vortex cavitation occurrence data. Therefore, the local circulation is considered as the most important evaluation parameter.

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Experimental studies were conducted on heat transfer characteristics of a JEST (Jet Explosion Stream Technology) -type loop thermosyphon. Similar to conventional loop thermosyphons, the present loop thermosyphon consists of an evaporator section, a condenser section, a vapor line and a liquid line. However, it has a unique technology termed JEST, which induces a jet inside the evaporator section to enhance the cooling performance of the loop thermosyphon. In experiments, the evaporator section was heated by a heating block and the condenser section was water-cooled by using a thermostatic bath. The temperatures, the pressure and the flow rate of the working fluid inside the loop thermosyphon were measured by changing the heat input to the evaporator section. Water was used as the working fluid, and a transparent evaporator was also employed to visualize the jet inside the evaporator section. From the experimental results, a stable operation of the present loop thermosyphon is confirmed. The image of the jet captured by a high-speed camera is shown. As the basic operational characteristics in the steady state, the maximum heat transfer rate and the maximum heat flux at the evaporator section are found to be 901 W and 127 W/cm², respectively under the condition that the temperature of the heated section is less than 90 °C. It is also shown that the heat transfer coefficient at the evaporator section is in a range from 17500 to 46500 W/(m²·K). The present loop thermosyphon works without using any external power, and then the cooling performance is significantly higher than traditional thermosyphons, heat pipes and liquid cooling systems.

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