Potential application of Rankine and He-Brayton cycles to sodium fast reactors

Traditionally all the demos and/or prototypes of the sodium fast reactor (SFR) technology with power output, have used a steam sub-critical Rankine cycle. Sustainability requirement of Gen. IV reactors recommends exploring alternate power cycle configurations capable of reaching high thermal efficiency.By adopting the anticipated working parameters of next SFRs, this paper investigates the potential of some Rankine and He-Brayton layouts to reach thermal efficiencies as high as feasible, so that they could become alternates for SFR reactor balance of plant. The assessment has encompassed from sub-critical to super-critical Rankine cycles and combined cycles based on He-Brayton gas cycles of different complexity coupled to Organic Rankine Cycles. The sub-critical Rankine configuration reached at thermal efficiency higher than 43%, which has been shown to be a superior performance than any of the He-Brayton configurations analyzed. By adopting a super-critical Rankine arrangement, thermal efficiency would increase less than 1.5%. In short, according to the present study a sub-critical layout seems to be the most promising configuration for all those upcoming prototypes to be operated in the short term (10–15 years). The potential of super-critical CO2-Brayton cycles should be explored for future SFRs to be deployed in a longer run.

► This paper has been focused on thermal efficiency of several Rankine and Brayton cycles for SFR. ► A sub-critical Rankine configuration could reach a thermal efficiency higher than 43%. ► It could be increased to almost 45% using super-critical configurations. ► Brayton cycles thermal performance can be enhanced by adding a super-critical organic fluid Rankine cycle. ► The moderate coolant temperature at the reactor makes Brayton configurations have poorer.