%0 Journal Article
%T Numerical Simulation of Size Effects on Countercurrent Flow Limitation in PWR Hot Leg Models
%A I. Kinoshita
%A M. Murase
%A A. Tomiyama
%J Science and Technology of Nuclear Installations
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/907364
%X We have previously done numerical simulations using the two-fluid model implemented in the CFD software FLUENT6.3.26 to investigate effects of shape of a flow channel and its size on CCFL (countercurrent flow limitation) characteristics in PWR hot leg models. We confirmed that CCFL characteristics in the hot leg could be well correlated with the Wallis parameters in the diameter range of . In the present study, we did numerical simulations using the two-fluid model for the air-water tests with £¿m to determine why CCFL characteristics for £¿m were severer compared with those in the range, . The predicted CCFL characteristics agreed with the data for £¿m and indicated that the CCFL difference between £¿m and m was caused by the size effect and not by other factors. 1. Introduction Reflux condensation by steam generators (SGs) is considered as one of the possible core cooling methods under hypothetical accident conditions in pressurized water reactors (PWRs). During the reflux condensation, the water condensed in SG U-tubes has to flow countercurrent to the steam generated in the reactor core. The core cooling performance heavily depends on the occurrence of countercurrent flow limitation (CCFL) in the hot leg which consists of a horizontal pipe, an elbow, and an inclined pipe. As reviewed by Al Issa and MacIan [1], many experiments have been conducted to investigate the CCFL characteristics in the hot leg, and empirical correlations have been proposed using Wallis parameters [2]. The review showed that many differences between CCFL data were simply due to geometrical effects. To compare CCFL characteristics in hot leg models, Vall¨¦e et al. [3] selected three geometrical factors: the horizontal pipe length to diameter ratio , the inclined pipe length to diameter ratio , and the elbow angle . They showed that even for similar geometrical factors, there was clear deviation between CCFL characteristics due to size effects. In order to evaluate effects of size better, numerical simulation using CFD (computational fluid dynamics) software is expected to be useful. In order to investigate effects of shape of a flow channel and its size on CCFL characteristics in hot leg models, we have previously done numerical simulations using a two-fluid model implemented in the CFD software FLUENT6.3.26 [4¨C6]. We found that the two-fluid model could reproduce CCFL characteristics under low-pressure conditions, and we confirmed that those in the hot leg could be well correlated with the Wallis parameters in the region of m [6]. On the other hand, CCFL characteristics for m
%U http://www.hindawi.com/journals/stni/2012/907364/