What question did this study set out to answer?

This research aims to evaluate the mechanical and thermophysical properties of boron carbide for its use in HTGR control rods.

January 17, 2026

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

Key Points

This research aims to evaluate the mechanical and thermophysical properties of boron carbide for its use in HTGR control rods.
Fabrication of 80% dense boron carbide via vacuum hot-pressing at 2100°C and 20 MPa.
Investigation of microstructure and temperature-dependent properties from RT to 1000°C.
Assessment of thermal shock resistance through multiple cycles of heating and cooling.
Compressive strength decreased from 1.46 GPa at RT to 0.90 GPa at 1000°C.
Thermal expansion coefficient increased significantly with temperature, indicating material behavior changes.
Repeated thermal shock cycles led to a 13.4% and 16.0% decrease in compressive strength after 60 and 100 cycles, respectively.

Abstract

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.

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