Observation of dissolved gas separation and accumulation in stationary water

Abstract

Unexpected gas accumulation in a safety system of nuclear power plants can damage system elements and degrade cooling performance. To prevent the gas accumulation, it is important to define the mechanism of gas accumulation occurred by separation of dissolved gas. In the current research, it is investigated how the variations of temperature and pressure affect separation of dissolved gases and accumulation of non-condensable gases. The experimental study is conducted on three subjects; gas accumulations by variations of (1) pressure, (2) temperature and (3) order of temperature and pressure changes. Before performing each experiment, demineralized water is stabilized under the initial condition (20 °C and atmospheric pressure) for more than 24 h. In a closed system, the gas accumulation cannot be occurred by pressure change. By heating water, the gas accumulation is generated. When the water is kept in higher temperature, the more gases are accumulated. Even if the water is cooled back to the initial condition, the accumulated gas is remained more than 50%. By changing the order of temperature and pressure variations, the gas is accumulated. In results, it is found that the gas accumulation can be generated if the solubility of dissolved gas becomes lower than initial condition. Additionally, it is found that the gas already accumulated in the system is difficult to remove without additional venting process.