Pressurizer spray line of PWR plant cools reactor coolant by injecting water into pressurizer. Since the continuous spray flow rate during commercial operation is considered insufficient to fill the pipe completely, there is a concern that a water surface exists in the pipe and may periodically sway. In order to identify the flow regimes in pressurizer spray piping and assess their impact on pipe structure, a two-phase flow experiment under steam-water condition was conducted. In the experiment, temperature fluctuation due to swaying was investigated. With a full-scale mock-up made of stainless steel, two-phase flow of 100°C steam and 60°C water under atmospheric pressure condition was investigated. The experiment revealed continuous temperature fluctuation of 5°C at edge of the water surface. Also, the fluctuation disappeared when concentration of non-condensable gas (Dissolved Oxygen) reached 1ppm. Even though DO concentration reached minimum of 20ppb and the gas phase could be considered almost 100% steam, no violent motion of the surface was observed which was concerned when steam condensation involved. Water levels and values of steady state heat transfer coefficient were estimated and compared with the values by Dittus Boelter correlation.

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