Design and analysis of self-actuated shutdown system in a small lead–bismuth cooled fast reactor

The safe operation of small lead-based fast reactors (LFRs) requires ensuring that the core temperature remains within a safe range. High temperatures will intensify the corrosive effect of lead–bismuth (LBE) on structural materials, seriously affecting the core’s lifespan. By burnable poisons (BPs) design, the risk of fuel and fuel rod cladding overheating under CRW accident in the LFR-180 core can be reduced. However, the core still faces the corrosion challenges induced by elevated LBE temperatures during and following the ULOF and ULOHS scenarios. In this research, the feasibility of the application of the self-actuated shutdown system (SASS) is explored, and the function of SASS is examined under anticipated transients without scram (ATWS). The calculation results demonstrate that the SASS can effectively mitigate the core equilibrium temperature following transients, thereby significantly reducing the risk of severe corrosion of structural materials. Designed in combination with SASS and BPs, the LFR-180BP-SASS improves the safety of the core during and following ULOF, ULOHS, and CRW events.