The study of two-phase flow instability attracts lots of attention due to its significance and complexity. Density wave oscillations are the most common dynamic instability, one type of flow instability, in two-phase systems. In this paper, various channe l models are constructed based on RELAP5. The 3×3 channel is chosen to analyze the stability and operation security of the system based on the comparison of stability boundaries. For the understanding of basic phenomenon, thermal hydraulic and transit time characteristics in the 3×3 channel are analyzed. The period of flow rate oscillations is an almost constant value along the axial direction. There is a phase lag between inlet and outlet which is nearly equal to 1/2 oscillating period. Flow oscillations may cause dryout when oscillations are divergent. This phenomenon is dangerous for reactors, and should be avoided. For the analysis of the decrease of CHF induced by oscillatory flow, the transit time is taken into consideration as an crucial parameter. The correlation developed by Masini et al. is the most accurate for transit time evaluation by comparison of different methods. Based on the analysis of parameters effect, transit time is positive with subcooled number Nsub. Transit time decreases linearly, and then transit time becomes flat with the increase of pressure when Nsub is fixed.
Wanga, S., & Yanga, B. W. (2017). Numerical Investigation on Thermal Hydraulic and Transit time Characteristics of Density Wave Oscillations. In Energy Procedia (Vol. 127, pp. 291–301). Elsevier Ltd. https://doi.org/10.1016/j.egypro.2017.08.111