Criticality studies of a nuclear light bulb engine

Abstract

Determination of the feasibility of a nuclear light bulb engine is the subject of a continuing research program, and some of the results of this research are discussed in the article. Critical masses of U-233 fuel are calculated for a seven-cavity, nuclear light bulb engine in which energy is transferred by thermal radiation from gaseous nuclear fuel through internally cooled transparent walls to seeded hydrogen propellant. Each of the engine cavities is 6 ft long and 2.3 ft in diameter. BeO is employed between the unit cavities, and layers of BeO and graphite surround the seven units to provide neutron reflection. Effects of variations in the total moderator mass, the amount of BeO between unit cavities, the ratio of end wall to radial moderator mass, the amount of tungsten seed in the hydrogen propellant, and the amount of hafnium required to shield fuel injection and recirculation system ducts are evaluated analytically. The analysis also includes factors affecting the kinetic behavior of a nuclear light bulb engine: variations in fuel region radius, mixed mean propellant temperature, nominal system operating temperature, system operating pressure, and the proportion by weight of tungsten seen in the hydrogen propellant. For one specific nuclear light bulb engine, prompt neutron lifetime from two-dimensional neutron diffusion theory is calculated to be 0.52 msec, and comparable critical masses for U-233, U-235, and Pu-239 are 35, 50, and 46 Ib, respectively, from one-dimensional neutron transport theory calculations.