System design optimization for multimegawatt space nuclear power applications

Abstract

The results of a design and optimization study of the Pellet Bed Reactor System Concept (PBRSC) for meeting the multimegawatt power needs of some Strategic Defense Initiative (SDI) missions during both alert and burst modes of operation are presented. The power system consists of four modules, each capable of providing up to 165 MWe during the burst mode and 3.3 MWe during the alert mode. This modular approach provides redundancy, with low-mass penalty, and it increases the power plant's survivability by requiring an attack force to destroy many independent power modules. Results indicate that the specific power of a hydrogen-cooled Pellet Bed Reactor/potassium Rankine cycle module (3.8 kWe/kg) is superior to a closed-loop Brayton cycle module (3.1 kWe/kg), but comparable with an open-loop Brayton cycle module (3.8 kWe/kg). The comparison established that the closed-loop Brayton cycle module needs about 10 times higher compressor power than the Rankine cycle module, resulting in a lower specific power. Additionally, the savings in the radiator mass resulting from the higher efficiency of the closed-loop Brayton cycle module (20% vs 17% for Rankine cycle module) is offset by the higher heat rejection load caused by the higher reactor thermal power to compensate for the higher compressor power. Analysis also established that the combined masses of the hydrogen tank and the attached refrigeration unit of the open-loop Brayton cycle module favorably compare with those of the radiator and the vapor generator for the Rankine cycle module.