Boron carbide for HTGR control rods: Sintering, temperature‐dependent properties, and thermal shock resistance

Abstract To evaluate the applicability of 80% dense boron carbide (B 4 C) for control rods in high‐temperature gas‐cooled reactors (HTGRs), a sintered body was fabricated from nuclear‐grade powder via vacuum hot‐pressing (2100°C, 20 MPa). Its microstructure, temperature‐dependent mechanical/thermophysical properties (RT–1000°C), and thermal shock resistance were systematically investigated. The microstructure shows the grains form an interconnected skeletal structure with uniformly distributed pores, beneficial for helium release. Compressive strength decreased from 1.46 (RT) to 0.90 GPa (1000°C), while the elastic modulus decreased from 285.5 to 266.4 GPa. The critical irradiation dose was calculated as ∼2.19×10 2 6 cap/m 3 , indicating enhanced swelling tolerance due to porosity. The thermal expansion coefficient increased from 3.05 × 10 − 6 °C − 1 (RT) to 6.02×10 − 6 °C − 1 (1100°C), and thermal conductivity decreased from 9.77 W/(m·°C) to 6.29 W/(m·°C). Predicted thermal conductivity values fell below 4 W/(m·°C) for burnups >5×10 2 6 cap/m 3 . After 60 and 100 thermal shock cycles (1000°C ↔ 125°C), compressive strength decreased by 13.4% and 16.0%, respectively, with transgranular fracture dominating. Theoretical evaluation of the critical temperature difference revealed that rapid cooling from high temperature induces microcracking. This study provides essential data and theoretical support for assessing the in‐core safety of porous B 4 C under HTGR conditions.