Effects of Transition Metals (TM = Nb, Ta, and Zr) on Thermodynamic and Electronic Properties of Advanced (Th ₁ − x TM x )C ( x  = 0.1 and 0.2) Fuels: A First‐Principles Study

In the development of advanced nuclear fuels, we investigated how transition metals (TM = Nb, Ta, Zr) affect the thermodynamic and electronic properties of thorium monocarbide (ThC) using first‐principles calculations. We modeled six ternary carbide compositions (Th 1− x TM x )C with x = 0.1 and 0.2 to predict key properties including heat capacity, entropy, Gibbs free energy, and bulk modulus across 0 K–1800 K. Results show that (Th 1− x Ta x )C has the lowest equilibrium energy and smallest volume, whereas (Th 1− x Zr x )C maintains the highest thermal conductivity and mechanical rigidity. Notably, (Th 0.8 Ta 0.2 )C exhibits significant phonon scattering and structural softening. Bonding charge density analysis reveals strong covalent Nb‐C bonds and intensive Zr‐C interactions, providing critical atomic‐level insights to accelerate development of next‐generation Th‐based nuclear fuels.