Multiple reheat helium Brayton cycles for sodium cooled fast reactors

Sodium cooled fast reactors (SFR) traditionally adopt the steam Rankine cycle for power conversion. The resulting potential for water–sodium reaction remains a continuing concern which at least partly delays the SFR technology commercialization and is a contributor to higher capital cost. Supercritical CO2 provides an alternative, but is also capable of sustaining energetic chemical reactions with sodium. Recent development of advanced inert-gas Brayton cycles could potentially solve this compatibility issue, increase thermal efficiency, and bring down the capital cost sufficiently to compete directly with light water reactors. In this paper, helium Brayton cycles with multiple reheat and intercooling states are presented for SFRs with reactor outlet temperatures in the range of 510–650 °C. The resulting thermal efficiencies range from 39% to 47%, which is comparable with supercritical recompression CO2 cycles (SCO2 cycle). A systematic comparison between the multiple reheat helium Brayton cycle and the SCO2 cycle is given, considering compatibility issues, plant site cooling temperature effect on plant efficiency, full plant cost optimization, and other important factors. The study indicates that the multiple reheat helium cycle is the preferred choice over SCO2 cycle for sodium cooled fast reactors.