飽和水の液中フラッシングの研究

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Recently, the research and development on advanced passive safety reactors with a water filled containment have been done in some countries whose aim is at the safety improvement of the nuclear reactor. An experimental study on a saturated high-pressure water discharging into a water pool was performed. The purpose of the experiment is to clarify the phenomena that occur by a blow-down of the water from the pressure vessel into the water-filled containment in the case of a wall-crack accident or a LOCA in a passive safety reactor. The results show that a flashing oscillation (FO) occurs when the water discharges into the pool, under specified experimental conditions. The range of the flashing location oscillates between a point very to and some distance away from the vent hole. The pressures in the vent tube and water pool constantly fluctuate due to the flashing oscillation. The pressure oscillation and alternating flashing location might be caused by the balancing action between the supply of saturated water, flashing at the control volume and steam condensation on the steam-water interface. The frequencies fo FO,or frequencies of pressure oscillation and alternating flashing location, increased as water subcooling increased, and as discharging pressure and vent hole diameter decreased. Nozzle length little affects on the frequency. It means that the location where the flashing occurs and steam generates, at the nozzle side on in the pool, does not affect on the frequency of FO.A linear analysis was conducted using a spherical flashing bubble model in which the motion of bubble is controlled by steam condensation. The effects o these parameters on the period of FO in the experiments can be predicted well by the analysis.