Experimental analysis of the flow behavior in the safety injection tank of APR1400

Abstract

Advanced Power Reactor 1400MWe (APR1400) has four Safety Injection Tanks (SIT) in the Emergency Core Cooling System (ECCS). Because SIT has a key role in the safety of the nuclear power plant, the performance of the SIT should be validated. The amount of ECC water discharge flow rate from the SIT and possible threat caused by nitrogen entrainment are the target of the validation. There were several researches which tried to evaluate the performance of SIT, including full-scale experiment and computational approaches. The attempts were successful to validate the mass flow rate of ECC water. However, the computational model of the SIT still need an improvement to demonstrate the nitrogen entrainment during the flow mode transition accurately. Fluidic device was introduced to the SIT for the passive control of the discharge flow rate of ECC water. The fluidic device has complicated structures to develop swirly flow in the device which hinder the computational analysis of the SIT. As the first step of figuring out the appropriate modelling of the SIT, the experimental analysis of the one-tenth scale model of the SIT was carried out with the visualization of the fluidic device. The fluidic device was simplified as a single control port and a single supply port structure of which the original fluidic device has 4 control ports and 4 supply ports. The experiment was done at the room temperature and the SIT was pressurized by nitrogen gas to the 10 bar. The discharge water flow rate, the pressure inside the SIT, the pressure difference over the fluidic device, the temperature inside the SIT were measured. The flow behavior in the fluidic device was observed by the camera. The discharge mass flow rate ratio of high flow mode and low flow mode is between 4 to 5. About 39% of nitrogen gas in the SIT was discharged during the flow mode transition. Nitrogen entrainment was clearly observed by the form of bubbles in the fluidic device. The results were used to validate the system code results. The results matched well at the low flow mode.