Transient thermal hydraulic analysis of a small passive lead–bismuth eutectic cooled fast reactor

•The proposed LFR-180 design presenting a compact, passive, and long-life LFR.•LFR-180 incorporates H-OTSG for steam generation and DRACS for decay heat removal.•LFR-180 is a fully passive reactor requiring no intervention in 149.1 h after shutdown.•H-OTSG serve as active safety system heat exchangers can effectively control the PCOT.•LFR-180 startup process is straightforward with no need for auxiliary heat. The lead–bismuth eutectic cooled fast reactor (LFR) emerges as a cutting-edge technology in nuclear reactor design. This study introduces a compact, passive, and long-life LFR reactor LFR-180. The LFR-180 incorporates modular helical-coiled once-through steam generators (H-OTSG) and direct reactor auxiliary cooling systems. This integration enables the generation of superheated steam and passive safety features of the LFR-180, eliminating the necessity for a water-steam separation device and contributing to enhanced power generation efficiency. A detailed transient thermal hydraulic analysis is conducted with tailored models for LBE solidification and H-OTSG thermal hydraulics. Results demonstrate that LFR-180 is a fully passive reactor, requiring no intervention up to 149.1 h after shutdown. The H-OTSG can serve as the heat exchangers of the active safety systems that can effectively reduce the peak core outlet temperature from 1003.6 K under the SBO accident to 724.2 K after shutdown.