In the case of a severe accident, such as a loss of power supply, it is necessary to keep the nuclear power plant in a safe condition. Therefore, steam-water injectors (SI) have been attracting attention as a device that can cool the plant without power supply in the event of a severe accident. In a SI, the steam condenses by direct contact between steam and water interface. As the steam condenses, negative pressure is generated, and a force that attracts water is generated. The SI can process a large amount of cooling water with this force. It can also function as a reactor condenser for nuclear reactors due to its high condensation performance. There are some characteristics of SI that the discharge pressure is expected to exceed the inlet pressure after being accelerated at the throat, and it has a very simple structure with converging-diverging part, which is expected to reduce the cost of installation and maintenance. Previous studies have indicated that GROLMES et al. (1968) inferred the flow in the reduced test section by measuring the void fraction and MIWA et al. (2018) suggested a relationship between internal flow and the operating range of SI, referring to the results inferred by GROLMES et al. (1968). Although these existing studies have suggested some relationship between the internal flow and the operating range, the relationship between the stability of the water jet and the behavior of the SI has not been clarified.

Therefore, the aim of this study is to clarify the effect of water jet behavior on the operating range of SI. The taper angle of the water jet outlet was varied and the relationship between the water jet behavior and the operating range was investigated. In this study, experiments were conducted using two types of taper angles at the water jet outlet: 20 and 7 degrees. As a result of detailed observation inside the SI, it was confirmed that the water jet with the taper angle of 7 degrees was less spreading than that with the taper angle of 20 degrees. In the operating range of this experiment, no significant difference was observed when the taper angle of the water jet was changed. However, it is suggested that the water jet with a certain degree of dispersion might be better in terms of heat exchange due to large surface area. These results suggest that the stability of the water jet is a necessary but not a sufficient condition for operation.

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