Abstract
The high-temperature thermodynamical properties for the actinide monocarbides and mononitrides ThC, ThN, UC, UN, PuC, and PuN are calculated from first-principles electronic-structure theory. The electronic structure is modeled with density-functional theory (DFT) and is fully relativistic, including the spin-orbit interaction. Furthermore, the DFT is extended to account for orbital–orbital interactions, by means of a parameter-free orbital-polarization (OP) technique, that has proven to be essential for the 5f electrons in plutonium. Strong anharmonicity and the temperature dependence of the lattice vibrations are captured with the self-consistent ab initio lattice dynamics (SCAILD) method. The calculated free energies and heat capacities are compared to published results from quasi-harmonic (QH) theory, and experiments, where available. For the uranium and plutonium compounds, we make use of CALPHAD assessments to help evaluate the theory. Generally, our anharmonic relativistic approach compares well with both CALPHAD and experiments. For the thorium compounds, our theory is in good accord with QH modeling of the free energy at lower temperatures but for the heat capacity the comparison is less favorable.
Highlights
Introduction for Actinide Monocarbides andActinide carbides and nitrides are of practical importance as possible nuclear fuels for Generation-IV reactors [1,2]
The QH approach, is known to be less predictive at higher temperatures [8,15]. We address these shortcomings in modeling by combining advanced first-principles electronic structure with a lattice-dynamics method that can treat strong lattice anharmonicity at high temperatures
We recently studied the thermodynamics for plutonium monocarbide [15] and th results from that investigation are included here with only minor modifications
Summary
Introduction for Actinide Monocarbides andActinide carbides and nitrides are of practical importance as possible nuclear fuels for Generation-IV (fast neutron fission) reactors [1,2]. The suitability of the nuclear carbide and nitride fuels is still being evaluated and fundamental research, experimental and modeling, has increased significantly in recent years [3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18]. These radioactive and toxic compounds are not trivial to work with and their material properties at higher temperatures, central for nuclear fuels, are difficult to measure accurately. From a modeling point of view, the electronic structure is complex, and the high temperatures of interest for fuels cause the atoms to behave in a challenging anharmonic fashion
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call