1 / 2017-10-13 07:21:24

Overview of Reflux Condensation in SBLOCA Tests of ATLAS Facility

SBLOCA, Reflux-condensation, CCFL, Loop seal clearing

The behavior of the reflux condensation heat transfer in a hot side steam generator (SG) U-tubes during a
cold leg (CL) pipe and a direct vessel injection (DVI) line break in small break loss-of-coolant accident
(SBLOCA) tests of the ATLAS facility was investigated including MARS code calculations. Among the
SBLOCA tests, a 600-CL pipe and 50%-DVI line break SBLOCA test were selected to investigate the behavior
of the reflux condensation. A reflux condensation heat transfer seemed to occur from the time the SG Utubes
were half-empty to near the loop seal clearing (LSC). It was found that a transition regime existed
between the reflux condensation heat transfer and reverse heat transfer. The remaining reflux condensate
in SG U-tubes owing to the counter-current flow limit (CCFL) phenomenon and a separating effect
of liquid carry-over and/or entrainment with steam moisturizing seemed to affect the thermalhydraulic
behavior of the transition regime. It was also found that the steam flowrate of the loop pipings
and SG U-tubes seemed to have a strong effect on the duration time of the transition regime, e.g., a larger
steam flowrate results in a longer duration. From a comparison of the reflux condensation behavior
between the ATLAS tests and MARS code calculations, overall qualitative agreements were found
between the two cases. The largest discrepancies were found in the SG inlet plenum water level between
the two cases, and the authors suggest that the combination effects of the remaining reflux condensate in
SG U-tubes and a separating effect of liquid carry-over and/or entrainment with steam moisturizing are
the reasons for the discrepancies in the water levels of the SG inlet plenum, which seems to be difficult to
simulate in the current version of the MARS-KS code.