Hot leg flow characteristics during two-phase natural circulation in pressurized water reactor

The characteristics of two-phase flow in the hot legs of a PWR under off-normal conditions of two-phase natural circulation was studied experimentally using the ROSA-IV Large Scale Test Facility (LSTF). The LSTF is a 1/48 volumetrically-scaled simulator of a Westinghouse-type PWR. The cocurrent flow of steam and water through the hot legs formed a horizontally stratified two-phase flow during two-phase natural circulation. However, a flow regime transition to non-stratified flow occurred at the leg downstream end such that liquid could be pushed up by interfacial drag into the steam generator located above the hot leg. For relatively large two-phase natural circulation rates, this flow regime transition included a three-dimensional hydraulic jump since the hot leg flow was supercritical. (orig.)