Development of core-wide and regional stability test facility, SIRIUS, that simulates void reactivity feedback, and stability evaluation

The SIRIUS facility was designed and constructed for highly accurate simulation of core-wide and regional instabilities of the BWR. A real-time simulation was performed in the digital controller for modal point kinetics of reactor neutronics and fuel-rod conduction on the basis of measured void fractions in reactor core sections of the thermal-hydraulic loop, which simulates thermal-hydraulics of a natural circulation BWR. A solid-state, series-regulated power supply, that plays a role of simulation output, was designed to attain fast response speed without loss of accuracy. A noise analysis method was performed to calculate decay ratios from dominant poles of a transfer function by applying AR method to time series of the core inlet flow rate. Experiments were conducted with the SIRIUS facility for the nominal operating condition of 3.13GWt natural circulation BWR. Channel and regional stability decay ratios were determined to be 0.38 and 0.54, respectively, which indicates sufficient margin for the instabilities. Experiments were extended to evaluate the stability sensitivity of the design parameters such as the power profile on the basis of three-dimensional steady-state analysis, the void reactivity coefficients, the core inlet subcooling, and the thermal conductance of the fuel rod.