Various types of large nuclear space power systems a r e being investigated in support of missions projected for the post-1980 period. Among the approaches being considered to meet projected needs a r e the potassium Rankine cycle, Brayton cycle, and thermionic systems operating a t relatively high temperatures in order to achieve high performance. All these systems require refractory alloys for structural purposes and employ alkali metals as process fluids. Heat for driving the systems would be supplied by a liquid-metal-cooled fast reactor. In the potassium Rankine engine, liquid potassium is vaporized in a boiler and used to power a vapor turbine similar to a central station steam-electric powerplant. Inert gas is compressed, heated, and expanded through a turbine in the Brayton cycle similar to air in the jet engine. Thermionic systems are dependent upon boiling electrons off a hot nuclearly heated surface and collecting them on a colder adjacent surface. The Rankine engine is characterized by a moderate system efficiency and small radiator; the Brayton cycle usually exhibits a high efficiency with a relatively large radiator but a relatively low system efficiency. The system specific weights f o r the Rankine and Brayton engines are approximately the same, while that of the thermionic system would be higher. Technology programs have been conducted in support of all three types of systems and, in particular, considerable effort has been placed on characterizing the refractory alloys which would be required f o r the construction of the systems. Papers presented in this report are the result of these refractory-alloy technology programs.
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