In a wall crack accident or loss-of-coolant accident (LOCA) in an advanced reactor with water filled containment, high pressure saturated water is discharged from the pressure vessel into the low-pressure, low-temperature water of the containment. The discharged saturated water causes flashing and generates steam. Steam is then condensed by the water in the containment. This paper describes our study of high pressure saturated water that rapidly contacts low-pressure, low-temperature water. The purpose of the study was to clarify the transient phenomena that occur when high pressure saturated water blows down from a pressure vessel into a water filled containment during a wall crack accident or LOCA in an advanced reactor. The experimental results revealed that flashing of high-pressure saturated water and a subsequent water hammer occurred under the specified experimental settings. Pressure peaked when steam generation or flashing occurred at the wall surface and the flashing steam condensed. After the peak, pressure oscillated and reached equilibrium condition in a short time. The pressure oscillation might have been caused by a balancing action between the flashing of high pressure saturated water and condensation of the steam generated by flashing in low-pressure, low-temperature water. To check the results of the experiments, numerical analyses were conducted. The numerical results cleared the mechanism behind flashing hammer phenomenon.

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