Supercritical steam Rankine cycle design optimization for molten salt reactor application

Abstract

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 MWth 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 degrees 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 degrees C and 401 degrees 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 degrees 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.