On the Dust-curtain Model Gaseous-core Reactor for Space of a Radiation Shield in A

The interest in interplanetary space travel has stimulated much discussion on the desirability of using nuclear, rather than chemical, energy for the spacecraft propulsion. Comparisons of the relative merits of various propulsion systems have been extensively discussed in the literature. The results of such studies yield a diversity of conclusions, depending on the assumptions which are made in such an analysis regarding the rocket parameters, e.g. specific impulse, ratio of the gross weight to the propellant weight and to the propulsion thrust, etc. Suffice it to say, a flight mission, such as an interplanetary travel, would benefit greatly from the use of a high-impulse propulsion, which can best be achieved by means of a nuclear energy source. The principle of rocket propulsion rests on the production of a highly heated working fluid, called the propellant gas, that is expanded and ejected through a nozzle, thereby converting its thermal energy to directed kinetic energy. The heating of the propellant can be derived from chemical reactions of combustibles with a chemical system or nuclear reactions of fissile materials with a nuclear system. In a nuclear reaction the fissile material, such as uranium (U2 ') is the fuel and the thermal energy released by fission is transferred to the propellant, usually a gas of low molecular weight, e.g. hydrogen. This energy transfer can be achieved by the use of a solid core, which serves as an intermediate medium for the energy delivery to the propellant. Although the solid-core reactor has reached a prototype engine demonstration after a decade of development,' , it does not represent the optimum use of nuclear energy in a rocket engine. This stems from the fact that fission energy is released at very high levels (10 ev or K), which must be degraded in a solid core reactor to the order of 3,000' K, the limit of the operational temperature of a solid core heat exchanger. It is therefore desirable to use a gaseous core in which the fuel, in the form of highly energetic fission particles, and the propellant gas are intimately mixed, thus transferring energy directly through collision and radiation. The main difficulty in constructing a gaseous core reactor lies in providing a specific flow field for the gaseous mixture in the reactor cavity that fulfills the criticality condition for the nuclear chain reaction-and also provides minimum loss of fuel to the exhaust and of energy, in the form of high intensity radiation of neutrons and gamma rays, to the cavity wall. The radiation flux is largely created in the fission process but, in part, comes from absorption processes, the decay of radioactive fission products, and the scattering of neutrons, and is accompanied by some x-rays. These radiations can cause damage to materials, particularly organic materials