Transactions of the Korean Nuclear Society Autum Meeting Gyeongju, Korea, October 25-27, 2017 1 Scaling Analysis to Design an Air-Water Loop Seal Clearing SET Facility Using MARS-KS Code Muhammed Mufazzal Hossen a,b , Jun-Young Kang b , Byoung-Uhn Bae b , Kyoung-Ho Kang a,b* a University of Science and Technology, 217 Gajeong-ro, Yuseong-gu, Daejeon 305-350, South Korea b Korea Atomic Energy Research Institute, Dae-deok, Dae-ro 989-111, Yuseong-gu, Daejeon 305-353, South Korea *Corresponding author:khkang@kaeri.re.kr 1. Introduction Loop seal clearing (LSC) is one of the most important phenomena in a small break or medium break loss of coolant accident in a pressurized water reactor (PWR). The loop seal formation (LSF) is closely related to the depression of liquid level of core while LSC reduce the depression of liquid level of core. A typical PWR has U- shaped crossover pipes which connect the steam generator outlet plenum to the reactor coolant pump and water in this pipe is called loop seal. Steam venting through the break in a cold leg small break loss of coolant accident (SBLOCA) is achieved only after the water in at least one of the crossover legs is blown out to either the break or reactor vessel [1]. During a SBLOCA in a Westinghouse type PWR, the core liquid level is depressed temporarily before steam clears liquid out of the primary loop seals [2]. The LSC in SBLOCA is an important phenomenon that governs the whole thermal–hydraulic behavior of the primary system. In a physical sense, sustaining of a loop seal clearance can be interpreted using a countercurrent flow limitation (CCFL) or flooding condition suggested by Wallis [3].The most widely used correlations of CCFL phenomenon are Wallis type [4] and Kutateladze form [5] can be expressed as equation (1) and (2) respectively. Jg *1/2 + mJl *1/2 =c ……… (1) Kug *1/2 + mKul *1/2 =c ……… (2) Where, J * g=Jgρg 1/2 /[gD(ρl-ρg)] 1/2 ; J * l=Jlρl 1/2 /[gD(ρl- ρg)] 1/2 ; Ku * g= Jgρg 1/2 /[gσ(ρl-ρg)] 1/4 ; and Ku * l= Jlρl 1/2 /[gσ(ρl-ρg)] 1/4 . The parameter J * , Ku * J, ρ, g, σ, D, m, and c, are the dimensionless flux of Wallis type, dimensionless flux of Kutateladze type, superficial velocity of fluid, density, gravitational acceleration, surface tension, diameter, slope, and gas intercept, respectively. The subscript l and g are liquid and gas phase, respectively. On the basis of the significance of LSC phenomenon in the PWR safety analysis, a separate effect test (SET) facility for air-water fluid is required to investigate the thermal hydraulics phenomena comprehensively. The calculation of inlet superficial air velocity (Jair) is necessary for the design of air blower or air fan capacity to provide air into the loop seal which requires theoretical formulation on the basis of conservation of air-water flow in a SET facility with respect to the steam-water flow in an integral effect test (IET) facility. The main objectives of this study are to derive a generalized formula of Jair of SET facility with respect to steam-water IET facility by scaling analysis, to investigate the physical significance of the calculated superficial air velocity, and to verify the calculated Jair using MARS-KS code simulation for the proposed SET of LSC. 2. Scaling Analysis To get the inlet superficial velocity of air in a SET facility, it is decided to use dimensionless number, Wallis parameter Jg * and Kutataledge parameter Kug to ensure the similarity of governing phenomenon of air– water countercurrent flow. To preserve the non-dimensionalized superficial air velocity of a SET facility with respect to prototype superficial velocity of steam can be written according to Wallis form as equation (3). Jair * (SET, Patmospheric) =Jsteam * (Prototype, Pprototype) … (3) The equation (3) ultimately provides the superficial velocity of air for a SET facility as equation (4). Jair=(DR) 1/2 Jsteam{(ρsteam/ρair)(ρl,set-ρair)/(ρl,prototype -ρsteam)} 1/2 ……….. (4) Where, DR= DSET/Dprototype is the ratio of diameter and P is the pressure. If diameter and superficial steam velocity of prototype facility are known, Jair can be calculated using equation (4) from a known diameter of a SET facility. In a similar fashion, by preserving the Kutateladze parameter of a SET facility with respect to prototype facility, the inlet Jair for a SET facility can be found as equation (5). The required Jair for a SET facility does not depend on the diameter in case of Kutateladze form. Jair=Jsteam(ρsteam/ρair) 1/2 {(σair,l/σsteam,l)(ρl,set-ρair/ρl–ρsteam)} 1/4 ………… (5) The diameter of the proposed SET facility is selected as equal in vertical and horizontal pipe, and vertical height is equal in both upward and downward leg. The Wallis parameter, Jsteam *1/2 value varies from 0.53 to 1.11 and the Kutataledge parameter, kusteam varies from 1.75 to 8.23 in the ATLAS SBLOCA tests [3].The value of Wallis and Kutataledge parameter varies from 0.47 to 0.55 and from 1.81 to 2.54