Investigation of density wave instability in once-through superheated steam generators using SIGHT

Density-wave oscillation is the most common type of two-phase flow instability in the steam generators. A computer code SIGHT was derived to study on flow instability for the superheated steam generator under high pressure. The drift flux model was used for two-phase flow analysis. Linear, frequency-domain method was used for modeling and the flow stability was evaluated by Nyquist stability criterion. The unified and representative variables, namely water/steam mass flow density, water/steam enthalpy and liquid sodium temperature were selected to describe steady state and perturbations. The density perturbation of subcooled water was taken into account since the large subcooling degree of feedwater. The code has been tested against the existing experimental data and compared with results of past analysis code. Also the effect on flow stability caused by system parameters and density changes in subcooled water was analyzed. Lastly, preliminary stability thresholds were given for Steam Generator of China Fast Reactor 600 (CFR600) using SIGHT.