Analysis of parallel channel instabilities in the CANDU supercritical water reactor

The present work investigates the parallel channel density wave instability in the CANDU supercritical water reactor (SCWR) using a 1-D thermal-hydraulic model in the time domain. The model, which was used to analyze a single channel in-phase mode of instability in the SCWR, is extended for parallel channels in the reactor core to determine both in-phase and out-of-phase modes of oscillations considering the origination of the instabilities purely due to the thermal-hydraulic feedbacks without taking into account the influence of neutronic reactivity feedback effects. The capability of the proposed model to analyze the parallel channel instability is validated against the available experimental data. Extensive numerical investigations are carried out to determine the marginal stability boundary for each of the modes of oscillations in the working regime of the CANDU SCWR. The effect of the asymmetric heating power on the instability thresholds is also studied. Finally, the relative dominance between the in-phase and out-of-phase modes of oscillations at the operating regime of the CANDU SCWR is determined.