Nonlinear Dynamics of Flashing in a Natural Circulation Two-Phase Flow Loop under Low Pressure

摘要

We present a review of our recent work on stability and bifurcation analyses of a new model for natural circulation boiling water loop that allows local pressure dependence of water saturation enthalpy, and hence can capture start of boiling in the unheated riser section. Thermal hydraulics model is based on single- and two-phase flow. Results of steady-state and stability analyses of the thermal-hydraulics model compare well with the experimental data. For neutronics-coupled-thermal-hydraulic systems, stability boundaries (SBs) and 7.5% oscillation curves (representing types of bifurcations along SBs) are plotted in inlet-subcooling-total-power parameter space. Stability and bifurcation analyses show that supercritical and subcritical bifurcations can occur along the SBs. Results of numerical simulations agree with those of steady-state and stability analyses. Effects of design and operating parameters on stability are also reported.