Mechanism of loop seal clearance occurring at U-shaped pipe with air-water two-phase flow

•Mechanism of LSC phenomena is investigated by using the LOCAL facility.•Onset of the LSC is defined by several hydrodynamic variables.•Vertical upward flow shows the slug regime with single Taylor bubble at the onset of the LSC.•Rapid transition of flow regime causing the critical velocity of gas i...

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Bibliographic Details
Published in:Nuclear engineering and design 2020-04, Vol.359, p.110398, Article 110398
Main Authors: Kang, Jun-young, Hossen, Muhammed Mufazzal, Bae, Byoung-Uhn, Kim, Yeon-Sik, Lee, Jae Bong, Shin, Yong-Chul, Jeon, Woo Jin, Kang, Kyoung-Ho
Format: Article
Language:English
Subjects:
Critical velocity
Cross-over leg (COL)
Crossovers
High speed
High speed visualization
Light water reactors
Loop seal clearance (LSC)
Loss of coolant accidents
Multiphase flow
Rapid flow
Scaling analysis
Slug flow
Taylor bubbles
Two phase flow
Two phase flow regime
Visualization
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Summary:•Mechanism of LSC phenomena is investigated by using the LOCAL facility.•Onset of the LSC is defined by several hydrodynamic variables.•Vertical upward flow shows the slug regime with single Taylor bubble at the onset of the LSC.•Rapid transition of flow regime causing the critical velocity of gas is related to the LSC. Main purposes of the LOCAL (LOop seal Clearance separate effect test of ATLAS) facility are to investigate the effect of cross-over leg (COL) diameter at the loop seal clearance (LSC), to evaluate the two-phase flow regime through high speed visualization, and to suggest the mechanistic models for the LSC prediction at Small Break-Loss of Coolant Accident (SB-LOCA) in Light Water Reactors (LWRs). In this paper, we introduce a key mechanism of the onset of the LSC occurring at U-shaped COL with air-water two-phase flow condition. The onset of LSC is coupled with the flow regime transition at vertical upward and horizontal section of COL. Slug flow with single Taylor bubble results in decrease of pressure difference at vertical upward section and causes rapid flow regime transition at horizontal section from the stratified to the slug. The critical velocity of gas leading to flow regime transition at horizontal section can explain the onset of LSC and high speed visualization can provide the clear understanding of LSC phenomena at the local point of view.
ISSN:0029-5493
1872-759X
DOI:10.1016/j.nucengdes.2019.110398