SIT (Safety Injection Tank) with passive flow controlling device, has technical issues to be analyzed. The emergency core cooling water discharge flow rate from the SIT, pressure loss coefficient of the fluidic device, and nitrogen entrainment phenomena are them. In this paper, the technical issues of a SIT were discussed with the experimental analysis over the one-tenth scale model of the SIT. The experiment was carried out with the visualization of the fluidic device. The fluidic device was simplified as a vortex chamber connected with the single control pipe line and single stand pipe line. The experiment was done at the room temperature. The discharge water flow rate, pressure inside the SIT, pressure difference over the fluidic device, and temperature inside the SIT were measured. The discharge mass flow rate ratio of high flow mode and low flow mode was between 4 and 5. With initial pressure of 10 bar, 39% of nitrogen gas in the SIT was discharged during the flow mode transition. The percentage of the entrained nitrogen decreased through the decrease of the initial pressure. Nitrogen entrainment started when the water level is 7mm above from the top of the stand pipe which indicates the vortex sink in the SIT at the time. The nitrogen entrainment criteria was brought out with the concept of equilibrium water level which is the stand pipe water level to compensate the pressure loss at the control pipe. Entrainment of nitrogen last until the equilibrium water level reaches 19.5 cm with the initial pressure of 10 bar.
피동유량조절장치가 도입 된 안전주입탱크의 시간에 따른 방출유량, 유량조절장치의 압력손실계수, 1차 계통에의 질소혼입현상은 안전주입탱크 설계와 개선에 직결되는 주요 요소이다. 본 논문은 축소모형 실험을 통해 위 사항들에 대해 논하였다. 축소모형실험은 1/10 크기의 안전주입탱크와 가시화된 유량조절장치를 연결하여 상온에서 수행하였다. 고유속 모드와 저유속 모드에서 방출 유량의 비는 4~5였으며 초기 압력 10 바(bar) 기준 39%의 질소가 혼입되었다. 질소 혼입은 초기 압력과 관계 없이 안전주입탱크 내부의 수위가 스탠드 파이프 위 약 7mm 지점부터 시작되었다. 질소혼입이 중지되기 위한 기준을 정립하기 위해 균형수위개념을 도입하였다. 초기 압력 10 바 (bar) 기준 질소혼입이 중지되기 위하여 스탠드 파이프 내부에 19.5cm의 균형 수위가 확보되어야 함을 확인하였다.
