Development of BWR Regional Stability Experimental Facility SIRIUS-F, Which Simulates Thermal Hydraulics-Neutronics Coupling, and Stability Evaluation of ABWRs

To investigate the stability of a boiling water reactor (BWR), the SIRIUS-F facility was designed and built for highly accurate simulation of thermal-hydraulic (channel) instabilities and coupled thermal hydraulics-neutronics instabilities of the BWR. By using two sets of measured void-fraction distributions in a reactor core section of the SIRIUS-F facility, a real-time void-reactivity feedback simulation was performed on the basis of the modal point kinetics of reactor neutronics and fuel rod thermal conduction. A noise analysis method was performed to calculate decay ratios and resonance frequencies from dominant poles of transfer function based on the AR method using time-series measurement data of a core inlet flow of the facility. Channel and regional stability experiments were conducted for a wide range of operating conditions, including maximum power points along the minimum pump speed line and the natural circulation line of advanced BWR plants. The experimentally obtained decay ratios and resonance frequencies are in good agreement with those calculated by the linear stability analysis code ODYSY. The SIRIUS-F experimental results demonstrated stability characteristics as a function of power and revealed a sufficiently large stability margin even under hypothetical power level conditions.