Steam-Water Two-Phase Flow Testing Under Nominal Pressure and Temperature Conditions for Natural Circulation Performance of Chimney in BWRX-300 SMR

Abstract The BWRX-300 is a water-cooled, natural circulation, small modular reactor developed by GE Hitachi Nuclear Energy in cooperation with Hitachi-GE Nuclear Energy. BWRX-300 is equipped with passive safety systems and leverages the design and licensing of USNRC-certified ESBWR. The BWRX-300 uses a tall chimney above the core to provide natural circulation head to drive sufficient core flow and ensure fuel is operated within its thermal limits. Thus, calculated void fraction in the chimney is a key quantity for estimation of the natural circulation core flowrate. BWR transient analyses are performed with Transient Reactor Analysis Code, GE version (TRACG) which has been qualified for calculating thermal limits in BWRs. This extent of qualification includes the evaluation of core flow rate and evaluation of void fraction in chimney or upper plenum of BWRs. To support extending the TRACG qualification of void fraction evaluation to the large-diameter chimney of BWRX-300, additional test data were obtained with steam-water two-phase flow test and the void fraction modeling and calculation in TRACG were validated. The test was conducted in Hitachi Utility Steam Test LEading facility (HUSTLE) using a chimney test section, which was down-scaled to around 0.5 m in diameter. Distributions of the void fraction and the gas-liquid interfacial velocities in the chimney were measured by differential pressure gauges and the Wire-mesh Sensor (WS) for nominal BWR operating conditions of 7 MPa and 290 °C and flow conditions scaled from conditions of BWR-300 chimney at a range of reactor power levels. The average void fraction in the chimney estimated by the TRACG model and compared with the HUSTLE data. Consequently, the qualification of the void fraction estimation of the TRACG model was extended to the large-diameter chimney of BWRX-300.