The present study concerns itself with the condensation oscillation phenomena by steam-jetting into subcooled water through a sparger in the In-containment Refueling Water Storage Tank (IRWST) of Advanced Power Reactor 1400 (APR 1400) to mitigate the beyond design basis event.
The scaling methodology and the similarity correlation between the test facility and the real plant is implemented. The scaling parameters are derived by use of three governing equations: mass conservation equations, momentum conservation equations, and energy conservation equation. This scaling approach produces the global scaling parameters such as geometrical parameters, time constants and friction parameters. The steam cavity volume playing a major role in condensation oscillation phenomena is included in the scaling parameters. In the corroboration stage, various experimental tests are conducted. The scaling-related parameters experimentally considered are water temperatures, mass flux, discharge system volumes, tank sizes, source pressure, steam-jetting directions, and numbers of discharge holes. Each scaling parameter is ranked in terms of their relative importance for the condensation oscillation phenomena.
At around the water temperature of 80℃, unstable condensation occurs and the oscillation amplitude becomes its maximum. With an increase of the steam mass flux, the steam cavity enlarges and the oscillation amplitude increases. In low steam mass flux, water inertia plays an important role in the motion of the steam cavity. In high steam mass flux, the steam cavity infinitesimally oscillates.
When an additional volume is connected in with pipe run locations, the larger the additional volume, the oscillation amplitude decreases, accordingly. It is concluded that the additional volume acts like as another source of steam-jetting and provides a volume of dampening the perturbation wave translated upstream. The thickness of the boundary layer that encloses the steam cavity is found to be equal to the maximum length of the steam cavity formed. In order to preserve the scaling similarity, the thickness of the minimum boundary layer should be kept. Variations of the oscillation amplitude are small when steam-jetting directions are altered.
The Reynolds number, the Jacob number, and the Weber number are used to correlate the steam cavity length. The experimental ranges of Re, Ja, and $W_e$, are $7.06\times10^4 ~ 1.23\times10^6$, 10.82 ~ 43.27, $1.42\times10^4 ~ 1.23\times10^5$, respectively. Three key scaling parameters are identified and empirically correlated with the maximum amplitude of pressure oscillation: flow restriction coefficient, area ratio of discharge hole to steam cavity, and density ratio of water to steam. The concept of a reduction factor is introduced for estimating the oscillation amplitude of multi-hole spargers with test data from a single-hole sparger.
Based on the assumption that the condensation flux at equilibrium is equal to the mass flux through the discharge hole at equilibrium, the second order linear differential equation for the oscillation frequency can be derived. The density-weighted Strouhal number derived from second- and third-order linear differential equations are compared with experimental data.
