Spectrum-Dependent Burnable Poison Selection for Enhanced Safety and Neutronic Performance in an Epithermal Supercritical Carbon Dioxide-Cooled Reactor

This study investigates the neutronic performance of burnable poisons (BPs) in an epithermal spectrum supercritical carbon dioxide (S-CO2)-cooled reactor. Twelve candidate BP materials are systematically evaluated, including rare-earth oxides (e.g., HfO2, Er2O3, Eu2O3, etc.) and boron-based compounds (B4C and PACS). The deterministic neutron transport code KYLIN-I with the ENDF/B VI 45-group cross-section library is employed for analysis. According to the calculation results, Eu2O3 effectively suppresses the initial kinf of the epithermal-spectrum fuel assembly to ~1.2 with a relatively low weight fraction (~2.6%) while maintaining a total temperature coefficient (TTC) lower than −1.4 pcm/K throughout the entire burnup period. HfO2 and Er2O3, at approximately 15% weight fraction, achieve TTC values better than −2 pcm/K. Furthermore, both Eu2O3 and HfO2 contribute to maintaining a low, stable power peaking factor (PPF) below 1.24 throughout the burnup process. This study provides a theoretical foundation and technical support for designing an efficient and safe S–CO2-cooled nuclear reactor. It highlights the importance of selecting BP materials that are well-adapted to the neutron spectrum and optimizing the fuel assembly configuration accordingly.