LARGE-SCALE MULTIDIMENSIONAL PHENOMENA FOUND IN CCTF AND SCTF EXPERIMENTS

MURAO Y IGUCHI T AKIMOTO H IWAMURA T

Y. Murao et al., LARGE-SCALE MULTIDIMENSIONAL PHENOMENA FOUND IN CCTF AND SCTF EXPERIMENTS, Nuclear Engineering and Design, 145(1-2), 1993, pp. 85-95

18

INGLESE

Article

Nuclear Sciences & Tecnology

Nuclear Engineering and Design → ACNP

0029-5493

145

1-2

1993

85 - 95

ISI

0029-5493(1993)145:1-2<85:LMPFIC>2.0.ZU;2-0

Thermal-hydraulic behavior in the pressure vessel during the reflood p hase of a PWR-LOCA is discussed based on the results from tests with C ylindrical Core and Slab Core Test Facilities, which model a 1100-MWe- class PWR with a scaling ratio of about 1/20. Major findings on core t hermal-hydraulics are: (i) substantial water accumulation in the upper part of the core, (ii) radially uniform water accumulation, and (iii) fluid circulation and/or concentration to high power bundles. These m ulti-dimensional phenomena cause better core cooling in the high power bundle than expected from an evaluation model for licensing based on one-dimensional reflood experiments. After comparison with data from t he FLECHT low-flooding tests the substantial water accumulation is con sidered to be caused by recirculation flow. Based on small scale reflo od experiments, effect of local mass flow on heat transfer enhancement in film boiling was correlated and all phenomena except the flow conc entration effect were numerically well-simulated by using an analytica l model with this correlation. The flow concentration effect on core h eat transfer was empirically correlated with local power ratio. It was observed that the core coolability was enhanced by non-uniform fluid mixing between core flow and subcooled water from the hot legs for PWR s with combined-injection ECCS. This is a multi-dimensional phenomena. The heat transfer enhancement was also well-simulated with the above- mentioned model.