Point Defects Stability, Hydrogen Diffusion, Electronic Structure, and Mechanical Properties of Defected Equiatomic γ(U,Zr) from First-Principles

Abstract

At present, many experimental fast reactors have adopted alloy nuclear fuels, for example, U-Zr alloy fuels. During the neutron irradiation process, vacancies and hydrogen (H) impurity atoms can both exist in U-Zr alloy fuels. Here, first-principles density functional theory (DFT) is employed to study the behaviors of vacancies and H atoms in disordered-γ(U,Zr) as well as their impacts on the electronic structure and mechanical properties. The formation energy of vacancies and hydrogen solution energy are calculated. The effect of vacancies on the migration barrier of hydrogen atoms is revealed. The effect of vacancies and hydrogen atom on densities of states and elastic constants are also presented. The results illustrate that U vacancy is easier to be formed than Zr vacancy. The H interstitial prefers the tetrahedral site. Besides, U vacancy shows H-trap ability and can raise the H migration barrier. Almost all the defects lead to decreases in electrical conductivity and bulk modulus. It is also found that the main effect of defects is on the U-5f orbitals. This work provides a theoretical understanding of the effect of defects on the electronic and mechanical properties of U-Zr alloys, which is an essential step toward tailoring their performance.

First-Principles Study on Mechanical and Optical Behavior of Plutonium Oxide under Typical Structural Phases and Vacancy Defects

“… ( a ) Values of average sound velocity (ν m ), longitudinal wave velocity (ν l ), shear wave velocity (ν t ) of Pu 16 O 23 , Pu 16 O 22 , Pu 16 O 20 , Pu 16 O 18 using VASP. ( b ) Values of the Young’s modulus (E), Bulk modulus (B) and Shear modulus (G) (in GPa), and Poisson’s ratio ( ) of Pu 16 O 23 , Pu 16 O 22 , Pu 16 O 20 , Pu 16 O 18 are compared with the values of Pu 32 O 62 , Pu 32 O 60 , Pu 32 O 56 , Pu 32 O 52 calculated by Ghosh [ 47 , 48 ]. …”

High-Temperature Mechanical and Dynamical Properties of γ-(U,Zr) Alloys

“…Nowadays, the density functional perturbation theory (DFPT) and quasiharmonic approximation (QHA) have proved essential in drawing up ground-state phonon dispersion relations and physical properties. For example, several first-principle calculations have been performed in the literature to study the ground-state properties of UZr alloy [ 18 , 19 , 20 , 21 , 22 , 23 , 24 ]. However, DFT calculations are typically performed statically, implying that the calculations are mainly applied at 0 K. Our previous studies [ 25 ] also proved, via calculating elastic constants, that UZr alloy is mechanically unstable under ambient conditions.…”