STARTING AND CONTROL CHARACTERISTICS OF NUCLEAR ROCKET ENGINES

Abstract

The problem of the starting and control of a hypothetical nuclear rocket engine with a bleed cycle arrangement is studied parametrically with the aid of an analog computer. The study includes the investigation of both the open-loop (with a programed control rod ramp) and controlled system. Starts are considered with the reactor initially subcritical and critical. The open-loop system is inherently well behaved. Temperature changes are not as severe as power variations, although permissible temperature gradients may be exceeded. The initial transients of the uncontrolled system are due mainly to the time constants associated with thermal and mechanical processes, whereas the long-term transient is the result of the neutron precursor groups with long half lives. It is possible to control the temperature and pressure satisfactorily and to meet realistic limitations on maximum design temperature and temperature rise rates. Control is accomplished by a reactor core exit pressure reference feedback control of the turbopump system flow rate and a reactor core exit gas temperature reference feedback control of the reactor power output. Controlled but rapid transitions from initial to full power are possible, and changes in thrust at design conditions are performed rapidly without excessive temperature excursions. (auth)