This fact showed that FO was basically dominated by bubble motion in the pool water. The phenomena of flashing and condensation when saturated high-pressure water was discharged into pool water were clarified by that study. The study however, investigated only a steady flow condition after discharge was initiated.

This paper describes our experimental 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. To check the results of earlier experiments, experiments and numerical analysis were conducted for the case of saturated high-pressure water discharging into an air field. The test geometry was similar to a classical test case of rapid depressurization in a horizontal pipe initially filled with subcooled liquid (Edward's pipe). The acquisition of hydrothermal data on the phenomena will be indispensable for the detailed design and development of heat plants or reactors for marine use.

　

NOMENCLATURE

B average brightness in test section

A thermal diffusivity

e enthalpy

e_i differential brightness, defined by equation (1)

F steam generating ratio, defined by equation (A-4)

ΔF corrector for numerical calcuration

h_fg latent heat of evaporation

Ja Jacob number

P calculated pressure, defined by equation (A-10)

P_HO initial pressure of high-pressure saturated water

P_HP peak pressure of high-pressure saturated water

P_LO initial pressure of low-pressure water

P_a initial pressure of inertial layer under depressurization

q heat flux

R bubble radius

R⁺ nondimensional bubble radius

T temperature

ΔT liquid superheat. (T_∞-T_sat)

T_LO temperature of low-pressure water room

u velocity

u_r slip velocity

t time

t_r nondimensional time

x space

v specific volume

W weight

　

GREEK LETTERS

α void fraction

Γ steam generation ratio

ρ density

τ shearing stress

θ subcooling factor. (T_w-T_b)/(T_w-T_sat)

　

SUBSCRIPTS

b bulk

F expanding-layer

m average

v vapor

l liquid

I cell number

I_maxMaximum cell number

W inertial-layer

　

2. APPARATUS

　

Fig. 1 Apparatus

　

Figure 1 shows the apparatus used in the experiments. It consisted of a 10-liter high-pressure saturated water tank, which was equivalent to a pressure vessel; a 10-liter low-pressure, low-temperature water tank. which was equivalent to a water-filled containment; and a tube with an inside diameter of 21.7 mm connecting the two tanks. Rapid contact of high-pressure saturated water and low-pressure, low-temperature water (cold water) or air was produced by opening a valve that separated the two water columns in the horizontal tube [10]. The valve opening duration was 0.1 ms. A heater and cooler installed at the tanks controlled the pressure and temperature of the water. The experiments were performed with initial pressures in the high-pressure saturated water tank ranging from 0.2 MPa to 1.2 MPa. Initial pressure of the low-pressure water or air tank was atmospheric pressure. Pressures and temperatures in the tube and tanks were measured by semiconductor pressure transducers (with a natural frequency of 40 kHZ and bi-directional span of 0.5 MPa) and thermocouples, respectively. The output signals from these sensors were first transmitted to a fast Fourier transform (FFT) analyzer, then to a personal computer. The sampling rates of the data acquisition system were 50 kHZ for pressure measurement. The phenomena were observed by a high-speed video camera that operated at 2000 frames per second, with a backlit stroboscope.

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