BWRX-300’s Nominal Pressure and Temperature Testing (2): Steam-Water Two-Phase Flow Evaluations in Large Diameter Chimney Based on Void Fraction Measurement using Double-Plane Wire-Mesh Sensor

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. Like the 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. The TRACG system code has been qualified for calculating thermal limits in BWRs including the natural circulation ESBWR. To support extending the TRACG qualification to the large-diameter simplified chimney of BWRX-300, we have obtained additional data and shown the effectiveness of the measurement data in the previous study. This study aims to validate the void fraction estimation with the TRACG for the large-diameter chimney based on the measurement data using a Double-plane Wire-mesh Sensor (DWS) in a down-scaled chimney of around 0.5 m diameter. In Hitachi Utility Steam Test LEading facility (HUSTLE), void fraction distributions and velocities of the gas-liquid interface were measured by the DWS at nominal BWRX-300 operating conditions of 7.17 MPa and 289 ℃. The flow regimes in the chimney were discussed based on the void fraction distributions and representative scale of the dispersed phase measured by the DWS. Furthermore, the average void fraction in the chimney was estimated by the TRACG and showed good agreement with the HUSTLE test results. Consequently, we confirmed the validity of the TRACG estimation for the large-diameter chimney.