This paper describes the turbomachinery design considerations for a supercritical Rankine cycle waste heat power conversion system for use with the large helium closed-cycle gas turbine nuclear power plant under development by General Atomic Company. The conceptual designs of the ammonia turbine and pump are presented. The high density working fluid in the ammonia turbine results in small blade heights and high hub-to-tip ratios due to a combination of the properties of ammonia and the high degree of pressurization, particularly at the turbine exit. With the molecular weight of the ammonia working fluid being very similar to steam, the double-flow, multistage axial ammonia turbine bears a strong resemblance to modern steam turbines. Conceptual design work has been done in sufficient detail to support component cost estimates for the balance of plant economic studies. While an extensive design program is needed for the ammonia turbine, existing technology from the power generating and chemical process industries is generally applicable; and, with specialized design attention, the goal of high turbine efficiency should be realizable. The design studies have been specifically directed toward a nuclear closed-cycle helium gas turbine plant (GT-HTGR); however, it is postulated that the turbine design considerations presented could be applicable to other low temperature power conversion systems such as geothermal or industrial waste heat applications.

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