Supercritical steam Rankine cycle design optimization for molten salt reactor application

Supercritical steam cycles provide a commercially mature power conversion route for next generation molten salt reactors (MSRs), but the high melting points of chloride- and fluoride- based salts demand elevated steam generator (SG) feedwater temperatures to avoid salt solidification. This study models and optimizes three 300 MW th Rankine layouts—a Normal Supercritical Cycle (NSC), a Preheat Split Cycle (PSC) and a Recirculation Split Cycle (RSC)—using a MATLAB code that represents each component. Under current industry practice, the NSC attains 44.0 % efficiency yet lifts SG feedwater to just 272 °C, marginal for nitrate salts and inadequate for most chloride or fluoride. Diverting (PSC) or recirculating (RSC) 5–30 % of the SG steam raises feedwater to 392 °C and 401 °C, respectively, while cycle efficiencies remain above 44 %. These temperatures exceed the melting thresholds of Solar Salt, HITEC, carbonate and many chloride blends, providing at least a 100 °C freeze margin. The results demonstrate, for the first time, that careful flow-routing within a super-critical steam circuit can reconcile freeze protection of the MSR power plant and performance, showing that a super-critical steam Rankine cycle is a highly promising power-conversion option for MSR applications.