ICONE23-1367 THE THERMAL-HYDRAULIC BEHAVIOR OF SEAWATER IN AN INTERNALLY HEATED ANNULUS

Abstract

The progress of the 2011 Fukushima Daiichi nuclear disaster has been calculated by severe accident analysis codes in order to understand the causes of accidents and the current status of the reactors in the Fukushima Daiichi nuclear power plants. However, effects of seawater are not considered in these calculations, although the seawater has been attempted to inject into the reactors to cool down the nuclear fuels. The seawater provides a potential to affect the heat transfer due to the changes of the physical properties of the coolant. Besides, deposition of a scale may change thermal-hydraulic performance in the reactor pressure vessels. Although it is important to clarify these effects of the seawater on cooling of a heated surface, the conventional researches which evaluated these effects of the seawater quantitatively are hardly found. In order to make clear these effects, we have conducted an experiment with an internally heated vertical annulus using manmade seawater as a working fluid to measure basic thermal-hydraulic behavior of the seawater. In the present study, we measured heat transfer coefficient, boiling behavior and flow velocity distributions in the internally heated vertical annulus. Working fluids were pure water, manmade seawater and NaCl solution. The heat transfer coefficients were estimated by measuring temperature differences between a heater rod and these working fluids. The boiling behavior was observed with backlight of LEDs. The flow velocity distributions were estimated by a PIV (Particle Image Velocimetry) with fluorescent particles. These observations were conducted with a high speed video camera. From these experiments, the heat transfer coefficients of the manmade seawater was the same as that of the pure water in the heating condition without boiling. However, in boiling conditions, the heat transfer coefficients of the manmade seawater and the NaCl solution was larger than that of the pure water. From the observations with the high speed video camera, it is considered that the differences are caused by differences of boiling behavior in each working fluid. The velocity distributions in the manmade seawater and the NaCl solution were also different from that in the pure water in the boiling conditions. Therefore, although there is no obvious difference of the thermal-hydraulic behavior in the pure water, the manmade seawater and the NaCl solution in single phase flows, the thermal hydraulic behavior of the boiling flows is different in each fluid.