Evolution in the approach of Brayton cycle-space nuclear reactors

Because it is a widely recognized future dynamic space conversion system, the Brayton cycle has been studied in France since several years, especially within the framework of a limited space nuclear program. A single recuperated cycle of 20 to 30 kWe has been considered so far. However, possible applications could evolve, and the reactor concept and the conversion system should be more linked together. As an extension of past works, this paper presents a preliminary study of Brayton-Rankine combined cycles in the range of 50 to 100 kWe for a Lunar base power supply or planetary exploration for instance. Both Brayton-organic (toluene) and Brayton-steam combined cycles are investigated. A particular arrangement of HeXe heater and boiler or steam generator in series is proposed. It makes it possible to lower the reactor inlet temperature. Should this reactor be a water moderated, particle bed one, it could be of a much simpler design than in the case of a single direct cycle system. Key thermal, thermodynamical data are given. Net efficiencies of 25.8 to 27.6 percent are obtained, which is outstanding, given the reactor temperature profile. Consequences on the reactor design are mentioned