Nonlinear dynamic analysis of a two-phase natural circulation loop with multiple nuclear-coupled boiling channels

This study integrates the models developed previously by the authors to explore the stabilities, nonlinear dynamics and oscillation modes of a two-phase natural circulation loop with multiple nuclear-coupled boiling channels. The results indicate that both the pure thermal-hydraulic and nuclear-coupled boiling systems indeed have two instability regions, i.e. type-I and type-II instabilities, respectively. The pure thermal-hydraulic system tends to present in-phase mode of oscillations at the type-I boundary states and, in general, out-of-phase oscillations along with the type-II stability boundary. The oscillation modes may be affected by the configuration of parallel channels. By introducing the void-reactivity feedback together with neutron interaction, the coupling thermal-hydraulic and nuclear effects would induce complex influences on the system stability as well as the nonlinear oscillation modes. The in-phase mode, instead of out-of-phase mode, majorly dominates over the type-II boundary as the neutronic feedback is increased through void-reactivity coefficient. The complex nonlinear phenomena, such as complex periodic and chaotic oscillations, may appear in this multi-channel nuclear-coupled boiling natural circulation loop subject to a strong void-reactivity feedback (3Cα) coupled with a weak subcore-to-subcore neutron interaction (ɛij = 7.0).