Effects of Power Oscillations on Natural Circulation Flow Instability With a Neutronic-Thermo-Hydraulic Loop

Nuclear power in a water-cooled reactor changes with reactivity under the influence of temperature and void fraction. Effects of power oscillations on natural circulation are experimentally investigated with a neutronic-thermo-hydraulic loop to better understand neutronic-thermo-hydraulic effects. Heating power can be precisely controlled by a DC power supply. Both stable natural circulation flow and flow instability experiments are conducted. Amplitude of flow oscillations increases with the increase of amplitude of power oscillations for the stable natural circulation flow. Period and amplitude of power oscillations are compared with those of flow oscillations. Period of flow oscillations corresponds with the period of power oscillations due to the relative balance between driving force and resistance. Amplitude and period of power oscillations are changed to obtain stability boundary by keeping other parameters constant. Experimental results indicated that small amplitude and short period power oscillations has little influence of the stability boundary. However, power oscillations cause the premature of flow instability when period and amplitude of power oscillations are further increased. The destabilizing effects of power oscillations on natural circulation flow depend on the period and amplitude. The stability region reduces with the increase of amplitude and period of power oscillation in this experimental loop.