U.S. Department of Energy Office of Nuclear Energy Supercritical CO2 Brayton Cycle Energy Conversion Program

by Paul Pickard
Sandia National Laboratories

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The DOE Office of Nuclear Energy is investigating advanced power conversion systems for use with next generation nuclear power plants. The objective is to identify power conversion systems that have the potential to be more efficient and cost effective at the higher outlet temperatures of most next generation reactors. Brayton cycles are logical candidates for these higher temperature applications, and the supercritical CO2 Brayton cycle is well suited for this application with the potential for lower costs due to the relatively small size of the turbomachinery, and higher efficiency at the relevant outlet temperatures. The key issues for the Generation IV program included compression near the critical point of CO2 and control strategies in the split flow, recompression configuration. The current focus of the DOE S-CO2 program is on the development and operation of a small scale (~MWth class) demonstration loop to address these issues and provide experimental validation of analytic models used to design components and estimate performance. To support the development of this cycle, the DOE program is also conducting S-CO2 heat transfer experiments in compact heat exchangers and materials compatibility testing for the higher temperature applications. Single compressor loops are now in operations to test bearing and seal technologies, and turbo-machinery designs. Dual compressor loops will be operational later this year. Based on the current funding plan, a near MW (thermal) closed Brayton cycle loop will be operational in FY10 to complete the evaluation of key technologies, and provide a test bed for the demonstration of closed cycle operation. The next step in the DOE plan is to demonstrate the S-CO2 cycle at a sufficiently large scale to confirm system performance and control strategies for a commercially relevant sized system. The S-CO2 cycle is also considered to have potential for solar, advanced fossil, and other energy applications and DOE NE will seek broader participation with other DOE offices, industry, or international partners to identify the best approach for next level of scaling.