1992-08-03

Dynamic Neutronic and Stability Analysis of a Burst Mode, Single Cavity Gas Core Reactor Brayton Cycle Space Power System 929347

Reactor dynamics and system stability studies are performed on a conceptual burst mode Gaseous Core Reactor (GCR) space nuclear power system. This concept operates on a closed Brayton Cycle in the burst mode (on the order of 100 MW output for a few thousand seconds) using a disk Magnetohydrodynamic (MHD) generator for energy conversion. The fuel is a gaseous mixture of UF4 or UF6 and helium. Dynamic analysis is performed using circulating fuel, point reactor kinetics equations along with thermodynamic, lumped parameter heat transfer and 1-D isentropic flow equations. The gaseous nature of the fuel plus the fact that the fuel is circulating leads to dynamic behavior which is quite different from that of conventional solid core systems. For the examined transients, Doppler fuel temperature and moderator temperature feedbacks are found to be insignificant when compared to reactivity feedback associated with fuel gas density variations. The gaseous fuel density power coefficient of reactivity is found to be capable of rapidly stabilizing the system, within a few seconds, even when large positive reactivity insertions are imposed; however, due to the strength of this feedback, standard external reactivity insertions alone are found to be inadequate for bringing about significant power level changes during normal reactor operation. Additional methods of reactivity control, such as changes in the gaseous fuel mass flow rate or core inlet pressure are required to achieve desired power level control.

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