Effects of Transition Metals (Tm=Nb, Ta, and Zr) on Thermodynamic and Electronic Properties of Advanced (U1-Xtmx)C (X=0.1 and 0.2) Fuels:A First-Principles Study

Abstract

Ternary uranium carbides (U1-xTMx)C (TM = Nb, Ta, Zr; x = 0.1 and 0.2) are potential fuel candidates for next-generation nuclear reactors and nuclear thermal propulsion (NTP) systems due to their high melting points, excellent thermal properties, and chemical stability. In this work, a systematic first-principles study is carried out to evaluate the thermodynamic, electronic, and bonding behaviors of these carbides. It is revealed that the addition of Ta  enhances high-temperature mechanical strength and thermodynamic stability, as indicated by higher bulk modulus and lower Gibbs free energy. On the contrary, Nb significantly improves lattice thermal conductivity and bonding integrity owing to minimal lattice distortion, while Zr exhibits intermediate performance but offer advantages in structural compatibility and doping insensitivity, indicating their potential co-doping applications strategies. The variation tendencies in bonding characteristics in term of  bonding charge density are consistent with the calculated thermal and mechanical properties, providing an insights into the theoretical foundation for the compositional optimization of uranium carbide fuels, thus, to meet the demanding requirements of NTP and advanced high-temperature nuclear energy systems.

Keywords: Nuclear fuel, Transition metal doping, Actinide carbides, NTP