Closed Brayton-cycle configurations for Gas-cooled Fast Reactors (GFRs) and Very-High-Temperature Reactors (VHTRs)

This chapter focuses on the design of closed Brayton-cycle configurations for Gas-cooled Fast Reactors (GFRs) and Very-High Temperature Reactors (VHTRs), which make use of a reactor coolant such as helium. The gas turbine is integral to the technology of these concepts, because the unit power provision for its size is by far superior to the current technology. The power delivery is complemented by the high efficiency of the process while offering the main benefit of a direct cycle through the reduction of the plant size. The use of coolants such as helium eliminates the issues associated with reactivity of the coolant during the fission process. Based on these factors and the difficulties that might arise during the conceptual-design process, this chapter provides a descriptive account of the technological considerations for designing helium cycles for GFRs and VHTRs, especially the impact of different cycle configurations on the plant efficiency during normal Design-Point (DP) and Off-Design-Point (ODP) operations. In addition, the chapter examines design considerations for using different working fluids such as carbon dioxide and nitrogen for the power cycles, with comparisons made against each other including helium, whilst focusing on performance, cost, and technology readiness.