Reactor dynamics and stability analysis for two gaseous core reactor space power systems

Reactor dynamics and system stability studies are performed for two conceptual gaseous core reactor space nuclear power systems. The analysis is conducted using non‐linear models which include circulating fuel, point reactor kinetics equations and appropriate thermodynamic, heat transfer and one‐dimensional isentropic flow equations. The studies reveal the existence of some unique and very effective inherent reactivity feedback effects such as the vapor fuel density power coefficient that are capable of stabilizing these systems safely and quickly, within a few seconds, even when large positive reactivity insertions are imposed. However, due to the strength of these feedbacks, it is found that external reactivity insertions alone are inadequate for bringing about significant power level changes during normal operations. Additional methods of reactivity control such as changes in the gaseous fuel mass flow rate, or gaseous fuel core inlet pressure are needed to achieve the desired power level control.