This paper presents the stability analysis of a supercritical water-cooled system. A model of simplified supercritical water-cooled system is introduced and then its thermal-hydraulic equations, initial conditions and boundary conditions are given. Based on perturbation linearization and Laplace transformation, the transfer function between inlet mass flow rate oscillation and pressure drop oscillation of the simplified system model is established, and the characteristic equation of the simplified system model is derived. Applying control theory to solve the characteristic equation, the stability boundary points are found by judging whether the real parts of all roots solved by characteristic equation are greater than zero. A stability map which consists of these stability boundary points is generated by using both dimensionless sub-pseudo-critical number and trans-pseudo-critical number. An unstable region nearby the pseudo-critical point is determined. The effects of some important parameters on the stability map are investigated also by using decay ratio. The sensitivity analysis shows that the system is stabilized with a higher hydraulic system resistance, fluid inlet velocity or system pressure. It also shows that a longer heating zone, a harder pump characteristics or a larger gravitational acceleration (orientation angle) leads to a larger stability margin of the system. The stability map is also found to be not sensitive to a higher friction resistance or system pressure.

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