Multi-objective design optimization of an integrated regenerative transcritical cycle considering sensitivity in Pareto-optimal solutions

Small modular nuclear reactors (SMRs) are an emerging technology with many potential benefits to cost, manufacturing, and safety over more traditional reactor designs. The NuScale Power Module (NPM) is a pres-surized water SMR that uses natural convection to circulate its coolant. Variations of steam Rankine cycles have been the predominant design for power cycles in the nuclear energy space for decades, but ongoing research has suggested promising alternatives to be used in future designs. Previous works have suggested that a transcritical Rankine cycle with an organic working fluid like ethanol or methanol could have superior thermal efficiency compared to comparable steam Rankine cycles for mid-temperature applications. This study presents a design optimization and sensitivity analysis of an organic transcritical Rankine cycle (ORTC) with methanol as a working fluid, with a model of the NPM used as the primary cycle. Multi-objective optimization is used to analyze the trade-off between thermal efficiency and levelized cost of energy (LCOE) for this cycle design. All of the optimal designs identified in the multi-objective optimization show improvements in LCOE compared to the benchmark regenerative steam Rankine cycle at comparable thermal efficiencies, with LCOE being reduced by as much as 19.1% by using the ORTC. In the Pareto front, higher efficiency solutions use regenerative cycle designs, while lower LCOE solutions do not utilize regenerators. A sensitivity analysis of the optimal design points reveals that regenerative design points have greater sensitivity in both LCOE and thermal efficiency to the variation in the design parameters.