The Steam Injector (SI) is a passive pump with a simple structure that does not require an external power source nor moving machinery for the start-up. The SI constitutes five working parts: the inlet nozzle, mixing nozzle, throat, overflow line, and diffuser. Water and steam are injected into each inlet nozzles, and they flow separately through the mixing nozzle, in which the steam condenses onto the water jet surface. The water jet passes through the throat, and then it flows out from the diffuser where the pressure of the condensed fluid increases. Hence, the SI also possesses the capability as a jet pump, by obtaining a higher discharge pressure than the inlet steam pressure. Furthermore, it has high heat transfer characteristics resulting from direct contact condensation between steam and water. Therefore, SI has a high potential to be utilized as passive safety system that can continuously inject water into the reactor core or auxiliary safety systems in the event of station-black-out. At present, we evaluated the detailed characteristics of SI performances as passive coolant injector from both experimental and analytical approaches.

In this study, axial pressure and temperature measurements with flow visualization of SI were carried out. A detailed database of discharge pressure, internal axial temperature, and pressure distribution, the location of shock wave generation was established by changing the inlet conditions and back-pressure as well as other parameters, to clarify the optimal working conditions. The internal flow behavior of SI was visualized with a high-speed camera, and the images of internal flow characteristics were obtained. Furthermore, the one-dimensional numerical analysis model is improved, and the performance of SI is analyzed according to the experimental results.

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