飽和水の液中フラッシングの研究

近年来，一些国家以提高核反应堆的安全性为目的，对先进的充水安全壳被动安全反应堆进行了研究和开发。对饱和高压水排入水池进行了实验研究。本实验的目的是阐明在无源安全反应堆发生壁裂事故或失稳事故时，压力容器内的水向充水容器内排入所发生的现象。结果表明，在一定的实验条件下，水进入池内时，会发生闪动振荡。闪光位置的范围在离排气孔很近的一点和离排气孔一段距离的一点之间振荡。由于闪蒸振荡，排气管和水池内的压力不断波动。压力振荡和闪蒸位置交替可能是饱和水供应、控制容积闪蒸和蒸汽-水界面蒸汽冷凝之间的平衡作用造成的。随着水过冷度的增大、排气压力的减小和排气孔直径的减小，压力振荡和闪蒸位置的频率增大。喷嘴长度对频率影响不大。这意味着闪蒸发生和蒸汽产生的位置，即在喷嘴侧和池中，不影响FO的频率。采用由蒸汽凝结控制气泡运动的球形闪蒸气泡模型进行了线性分析。通过分析，可以很好地预测这些参数对实验中FO周期的影响。

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.