Start-up transient test simulation with and without void-reactivity feedback for a two-phase natural circulation reactor

In order to understand and identify the instability phenomena during the start-up of the reactor, a scaled experimental facility is designed based on the sound scaling approach. The scaling laws are used to obtain design parameters to maintain the similarities between prototype and experimental facility. Modified power scaling is used for transient tests. Four heater rods are used to simulate the chaotic flashing phenomena. In order to investigate the instability during the start-up procedure, start-up transient tests are performed with and without void-reactivity feedback for different core heat-up rate. These experimental results show that IMR is susceptible to instability during the start-up procedure at very low pressure. These oscillations are condensation induced oscillations and occur due to high subcooling in chimney section. It is investigated that, since amplitude of power oscillation is low, void-reactivity feedback effect does not affect the stability of the system for this type of given power transient.