Nuclear Fuels

The subject of the current research is understanding of the unusual properties of the nuclear fuel materials for IVth generation reactors, actinide compounds, namely uranium, thorium and plutonium carbides. Comprehensive studies of the electronic, magnetic, elastic, dynamical, and thermodynamical properties of various phases in the (U/Th/Pu)-C systems are to be carried out based on the first-principles calculations. The primary goal is an insight into the nature of the thermal expansion phenomenon, of actinide carbides and especially the negative thermal expansion of UC2. The origin of this phenomenon still remains unknown. Second main issue is to explore the effect of strong electron correlations and the spin-orbit coupling (SOC) on the electronic and magnetic structure as well as on the lattice dynamics of the defect-free and defected, from strong nuclear radiation, actinide carbides.

This grant was supported Czech Science Foundation, Grant No. GACR-17-27790S (2017-2019).

 

  • Lattice dynamics and thermal properties of thorium metal and thorium monocarbide – Phys. Rev. B 101, 075117, 2020.

    Thorium is a chemical element that is beginning to attract attention because of its potential use as a nuclear fuel. It is not easy to carry out experiments because of its radioactive nature, and therefore theoretical works are highly appreciated. Thorium contains only a small number of the 5f states, and it is generally accepted that these states are itinerant, that they form a chemical bond, and that their nature does not need to be corrected with... Read More

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  • ARTICLE: Pressure variations of the 5f magnetism in UH3

    Pressure variations of the Curie temperature of the 5f ferromagnet β-UH3 were studied using the Mo-alloyed hydride (UH3)0.82Mo0.18, which is stable in air and has very similar TC and magnetization per U atom. By means of ac magnetic susceptibility a linear decrease of TC was observed for pressures up to 3.2 GPa. The coefficient dTC/dp = −2.05 K/GPa gives dlnTC/dp = 1/T*dTC/dp ≈ −0.011 GPa−1. This value is smaller than expected for a 5f-band ferromagnet with relatively short U-U distances and suggests that UH3 may be more localized than expected. Among AnX compounds,... Read More

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  • ARTICLE: XPS, UPS, and BIS study of pure and alloyed β-UH3 films: Electronic structure, bonding, and magnetism

    Uranium hydride films with the β-UH3 structure were successfully synthesized using reactive sputter deposition. Their composition can be modified, if cooling the substrate to 177 K, by incorporating Mo as alloying element, in analogy to bulk nanocrystalline (UH3)-Mo hydrides. The films were in detail studied by in situ XPS (4f, 5d, 6p, valence band), valence-band UPS, and BIS, revealing variations of electronic structure with respect to U metal, confronted with ab initio calculations. We could identify certain ionicity in... Read More

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  • ARTICLE: Crystal Structure and Magnetic Properties of Uranium Hydride UH2 Stabilized as a Thin Film

    A new type of uranium binary hydride, UH2, with the CaF2 crystal structure, was synthesized in a thin-film form using reactive sputter deposition at low temperatures. The material has a grain size of 50–100 nm. The lattice parameter a = (535.98 ± 0.14 pm) is close to that in known Np (534.3 pm) and Pu (535.9 pm) iso-types. UH2 is a metallic ferromagnet with the Curie temperature TC ≈ 120 K. A very wide hysteresis loop indicates strong magnetocrystalline anisotropy. X-ray... Read More

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