Two-phase flow regimes in a large-diameter model of a PWR hot leg

Knowledge of flow regimes in the hot legs and the steam generators of a pressurized water reactor (PWR) is essential in understanding and predicting the overall system thermal-hydraulic response during a small-break loss-of-coolant accident (SBLOCA). Flow regime characterization becomes especially important when natural circulation conditions prevail (low flow rates and high quality) and the potential for breakdown in flow is enhanced. To characterize flow regimes in PWR hot leg geometry, an experimental investigation with 10.2-cm diam glass pipe was carried out. These results showed that valuable information can be obtained from atmospheric pressure air-water flow tests in reactor geometries. This paper describes some preliminary results of 30.5-cm pipe tests.