Because of the excellent properties of lead-based materials as reactor coolants, lead-based fast reactors have become a key type of fourth-generation advanced nuclear energy systems. A small passive long-life Lead–bismuth -cooled fast Reactor (SPALLER) is designed by the University of South China for profound research.

This study aims to improve the inherent safety and cost-effectiveness of lead–bismuth-cooled fast reactors, and determine the maximum core power of this kind of reactor.

Firstly, the SPALLER was taken as research object, and five steady-state limitations and two accident limitations were proposed to meet the transportation size, material durability, and long-term operational stability of the reactor core and ensure safety under accident conditions. Then, a neutronics maximum power calculation platform was built through Latin hypercube sampling and a Kriging proxy model whilst the steady-state limitations were considered as multi-objective optimization problems with complex multidimensional nonlinear constraints. Meanwhile, the neutronics maximum power and natural circulation power of SPALLER-100 at different core heights were calculated by taking the natural circulation ability of SPALLER-100 into account. Finally, a design scheme was obtained to meet the requirements of neutronic and thermal-hydraulic assessments of this reactor while producing maximum power. Consequently, during the full life-cycle of SPALLER-100, a safety analysis of three typical accident scenarios (loss of heat sink, transient over power, and coolant inlet temperature undercooling) was performed using a quasi-static reactivity balance approach.

The results show that the maximum core power can be increased from 100 MW to 120 MW, and the neutronics maximum power calculation platform has high accuracy with safe and economical maximum power scheme.

This study can provide reference for other types of natural circulation reactors to maximize power output.