Dynamic stability boundaries of a liquid metal cooled reactor system

Part of the reactor design process is the assessment of the impact of different design changes on predefined performance criteria including stability of the reactor system under different conditions. This work focuses on the stability analysis of a combined reactor and primary heat transport system where system parameters are free to vary, with particular interest in low reactor power, low reactor coolant flow conditions. Such conditions might be encountered, for example, after a loss-of-flow without scram in some passively safe reactor designs. Linear stability analysis based methods are developed to find the stability regions, stability boundary surface in system parameter space, and frequency of oscillation at oscillatory instability boundaries. Models are presented for the reactor, detailed thermal hydraulic reactivity feedback associated with coolant outlet and inlet temperatures, decay heat, and primary system. Developed stability analysis tools are applied to the system model. System parameters include integral reactivity parameters, decay heat primary system mass, coolant flow, and natural circulation flow. The resulting stability boundary surface and its associated frequency of oscillation surface in multidimensional system parameter space show the effect of system parameter changes. By adopting model parameters for a reactor design, a stability prediction procedure is illustrated.