Regional stability estimation of 1/3 MOX BWR-5 core with SIRIUS-F facility

The SIRIUS-F facility was designed and constructed for highly accurate simulation of channel instability, core-wide instability and regional instability of ABWR. A real-time simulation was performed by the modal-point kinetics of reactor neutronics and fuel-rod thermal conduction on the basis of a measured void fraction in a reactor core section of the facility. A noise analysis method was performed to calculate decay ratios and resonance frequencies from dominant poles of transfer function on the basis of the AR method using time series measurement data of a core inlet flow of the facility. By utilizing this method, one can estimate stability in any specific operating point online without assuming excess conservative conditions. 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 the BWR-5 core with one third of MOX fuels installed. The decay ratios and resonance frequencies are in good agreement with the analyses results calculated by design analysis code, ODYSY The SIRIUS-F experimental results demonstrated stability characteristics such as a stabilizing effect of the power, and revealed a sufficiently large stability margin even under hypothetical conditions of power level.