Design of a Self-Regulating Deep Space Nuclear Reactor

Graduation date: 2016An enabling technology for long duration, deep space missions is the availability of a\ud high power, long-lived power supply. The goal of this work is the design of a self-regulating\ud deep space nuclear reactor. The design objectives are to produce 250 kWth\ud for a 25-year period using the presence of a microgravity field to regulate power output.\ud System reliability is optimized by eliminating the use of mechanical moving parts and the\ud need for external input for operation - either from human or software controllers - while\ud building on the foundation of previous technology developments. To achieve the power\ud output objective, a nuclear reactor is fueled with Uranium-Zirconium Hydride fuel with a\ud coolant of sodium/potassium eutectic (NaK-78) circulated using electromagnetic pumps.\ud Uranium-235 and burnable poison concentrations are adjusted to achieve the mission\ud duration objective. Reactivity control is provided using an outer shield of liquid uranyl\ud sulfate solution. This shield is thermally isolated from the reactor core to permit operation\ud at a high temperature for thermodynamic efficiency while maintaining the reflector at a\ud lower temperature for good power feedback.\ud The novel concept of using a liquid reflector has two advantages: reactor operation is\ud permissible only in the presence of a microgravity field and in the event of an inadvertent\ud re-entry, the liquid reflector would volatize leaving the remaining structure inherently\ud subcritical. Once deployed to a microgravity environment, a wicking structure embedded\ud in the reflector fills with uranyl sulfate solution and the reactor becomes slightly super\ud critical. Reactor power level increases until fuel temperature reactivity feedback limits\ud power to the design goal of 250 kWth. Burnable poisons are used to compensate for the\ud negative reactivity effects of fission product buildup over time. In effect, the reactor can\ud operate only in a microgravity field.\ud This work also details the construction of a model for validating the shut down margin\ud criticality of TRIGA reactor storage racks. These racks are mounted in the reactor pools\ud and are used to store the fuel that is not in use. TRIGA zirconium hydride fuel is similar\ud to the fuel type that was ultimately calculated for use in the Self-Regulating Deep Space\ud Nuclear Reactor. In both situations a very strong prompt negative reactivity coefficient is\ud desirable. Zirconium hydride fuel is the most mature candidate for such applications