Assessment of regenerative reheating in direct Brayton power cycles for high-temperature gas-cooled reactors

Abstract

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Future world energy demand will require a sustainable energy generation system. Optimization of power cycles has become a key element to better exploit natural resources, to minimize waste production, and even to reduce fuel cycle cost. Aware of this, nuclear technology is developing what has been termed Generation IV designs. In particular, the high-temperature gas-cooled reactor (HTGR) concept is a promising technology to reach much higher thermal efficiencies than present nuclear power plants. By using a classical thermodynamic methodology, this paper demonstrates that regenerative reheating would significantly enhance the thermal performance of a reference Brayton cycle based on pebble bed modular reactor (PBMR) technology. The regenerative reheating is conducted by a live gas fraction (b) extracted from the coolant inventory exiting the nuclear reactor. Optimization of b results in efficiency values as high as 53 and 61%, respectively, under current and midterm technology scenarios. In addition, reheating would allow an effective and easy-to-conduct load-follow operation with no loss of thermal efficiency in the upper range of b. Even further, under the midterm technology scenario, reheating would make it possible to cogenerate H2 from the enthalpy content of the b fraction exiting reheater.