Effective momentum induced by steam condensation in the oscillatory bubble regime

Abstract

The spargers used in Boiling Water Reactors (BWR) discharge steam from the primary coolant system into a pool of water. Direct steam condensation in subcooled water creates sources of heat and momentum determined by the condensation regimes, called "effective sources" in this work. Competition between the effective sources can result in thermally stratification or mixing of the pool. Thermal stratification is a safety concern in BWRs since it reduces the steam condensation and pressure suppression capacity of the pool. In this work, we present semi-empirical correlations to predict the effective momentum induced by steam condensation in the oscillatory bubble regime, relevant for the operation of spargers in BWRs. A Separate Effect Facility (SEF) was designed and built at LUT, Finland, in order to provide the necessary data. An empirical correlation for the effective momentum as a function of the Jakob number is proposed. The Kelvin Impulse theory was also applied to estimate the effective momentum based on information about the bubble dynamics. To do this, new correlations for the bubble collapse frequencies, maximum bubble radius, velocities, pressure gradient and heat transfer coefficient are proposed and compared to available data from the literature. The effective momentum induced by sonic steam jets appears to be constant in a wide range of studied Jakob number. However, further experimental data is necessary at larger Jakob numbers and steam mass fluxes.

CFD Study of Thermal Stratification in a Scaled-Down, Toroidal Suppression Pool of Fukushima Daiichi Type BWR

“…The optimal pool depth is determined based on the prevalent pool parameters, such as pool temperature and steam outflow. Several researchers focused their thermal stratification studies on steam condensation regimes, such as complete condensation in the pipe [6][7][8], chugging [5,7,[9][10][11], jetting [12][13][14][15][16] and bubbling [4,[17][18][19][20]. The impact of type of condensation regime on the formation and disappearance of thermal stratification has also been a topic of concern.…”

“…Figure19. Temporal variation in bulk average temperature with respect to the elevation ranges in the pool for aspect ratios of (a) 0.5 (Case J) and (b) 2.0 (Case K); free surface temperature is area-averaged temperature.…”