Safety analysis of small modular natural circulation lead-cooled fast reactors SNCLFR-100 during unprotected loss of heat sink and protected loss of heat sink transients

Abstract To investigate the inherent safety characteristics of the small modular natural circulation lead-cooled fast reactor, SNCLFR-100, simulations were conducted for both the unprotected loss of heat sink transient (ULOHS) and the protected loss of heat sink transient (PLOHS) using the multi-physics coupled safety analysis program for lead-based reactors, MPC_LBE. A two-dimensional cylindrical model integrated core, heat exchangers, and coolant pools. During the ULOHS, the strong negative reactivity feedback triggered rapid power reduction, achieving shutdown by negative reactivity feedback. In the case of the PLOHS, the reactor’s natural circulation and negative feedback effects prior to reactor scram effectively prevented a sharp increase in core temperature. After the reactor scram, the temperature rise in the hottest channel of the core, caused by decay heat, was minimal. The results of this study provide valuable insights for the design and thermal-hydraulic analysis of lead-based fast reactors.