Available online at www.sciencedirect.com Nuclear Engineering and Design 238 (2008) 1525–1534 Air clearing pressure oscillation produced in a quenching tank by a prototype unit cell sparger of the APR1400 Seok Cho ∗ , Chul-Hwa Song, Choon-Kyong Park, Hwan-Yeol Kim, Won-Pil Baek Korea Atomic Energy Research Institute, 1045 Daedeokdaero (150-1 Deokjin-dong), Yuseong, Daejeon 305-353, Republic of Korea Received 30 January 2007; received in revised form 29 November 2007; accepted 5 December 2007 Abstract KAERI has performed a series of experiments to investigate the performance of a prototype sparger for the APR1400 in view of a dynamic load oscillation with a variation of the test conditions such as a discharged air mass, a submergence of the sparger, the valve opening time, and the pool temperature during an air clearing phase. The air mass and pool temperature are in the range of 0.8–1.5 kg and 20–90 ◦ C, respectively. The valve opening time can be adjusted within the range of 0.6–1.8 s. The maximum positive pressure amplitude, which is observed at the bottom of the quenching tank, is increased with the maximum header pressure of the sparger. The valve opening time has a considerable effect on the maximum amplitude. As the opening time decreases, the maximum amplitude at the tank wall is increased. Air mass and pool temperature, however, have a weak effect on the maximum amplitude. Oscillation frequency is decreased with an increase of the air mass in the range of 2.5–4.5 Hz. © 2007 Elsevier B.V. All rights reserved. 1. Introduction The Korean advanced reactor (APR1400), a light water reac- tor of a 4000 MW th class, is now being developed by KEPCO and KOPEC to be brought into commercial operation in 2010. The APR1400 adopts several safety features to enhance its safety and mitigate the severity of accident consequences, and an experimental program for a thermal hydraulic evaluation and verification of the new design features in the APR1400 is now in progress for selected items at the Korea Atomic Energy Research Institute (KAERI) (Song et al., 2000). One of the key features of the APR1400 is the In-containment Refueling Water Storage Tank (IRWST) which is integrated with the Safety Depressur- Abbreviations: ABB Atom, Asea Brown Boveri Atom (former ASEA Atom and currently Westinghouse Electric Sweden); APR1400, Advanced Power Reactor with 1400MWe; IRWST, In-containment Refueling Water Storage Tank; KAERI, Korea Atomic Energy Research Institute; KEPCO, Korea Electric Power Corporation; KOPEC, Korea Power Engineering Corporation; POSRV, Power Operated Safety Relief Valve; SDVS, Safety Depressurization and Vent System. ∗ Corresponding author at: Thermal Hydraulics Safety Research Center, Korea Atomic Energy Research Institute (KAERI), 1045 Daedeokdaero (150-1 Deokjin-Dong), Yuseong, Daejeon 305-353, Republic of Korea. Tel.: +82 42 868 2719; fax: +82 42 868 8362. E-mail address: scho@kaeri.re.kr (S. Cho). ization and Vent System (SDVS). This feature originated from a boiling water reactor, and it represents a significant advance in the safety of the APR1400, but it has not been adopted in any operating pressurized water reactor (Schrum, 1978; Kim and Bae, 2001). In the event of transients or a small break LOCA coincident with a steam generator secondary side heat removal unavailable, the pressurizer Pilot Operated Safety Relief Valves (POSRVs) provide the Reactor Coolant System (RCS) with an overpressure protection by discharging high-pressure steam through sparg- ers from the pressurizer to the IRWST, and the SDVS of the APR1400 provides the feed and bleed capability with the SIS (Safety Injection System) to maintain the integrity of the RCS and the reactor core. The actuation of the POSRVs results in a time-varying high energy and momentum flow from the pres- surizer into the IRWST. During the initial blowdown period, the air in a discharge pipe at an atmospheric pressure is rapidly compressed, and it bursts into the IRWST through spargers. Naturally these discharged bubbles are at a higher pressure con- dition than the surrounding water, and therefore they start to expand. Together with the ambient water in the pool, these bub- bles form an oscillating volume, which imposes the relevant hydrodynamic loads both on the structures submerged in the IRWST and on the IRWST boundaries (Fredell, 1981; Bae et al., 2001). 0029-5493/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nucengdes.2007.12.001