Title: Density functional theory calculations of the thermodynamic and kinetic properties of point defects in β -U

Abstract

Density functional theory (DFT) calculations of the thermodynamic and kinetic properties of point defects in the β phase of uranium are reported. Defect energies and entropies were calculated using 2 x 2 x 2 supercells and the Generalized Gradient Approximation (GGA) of Perdew-Burke-Ernzerhof (PBE) for the exchange-correlation potential. Due to computational cost, calculations of the vibrational properties governing entropies were performed by only displacing atoms within (roughly) the 3rd or 4th nearest neighbor shell of the defect, which implicitly assumes that atoms beyond this distance are unaffected by the defect. Migration barriers were estimated by nudged elastic band (NEB) calculations. The low symmetry of the β-U phase (the unit cell is tetragonal and contains 30 atoms) results in many point defect configurations and even more migration pathways. A connectivity map, starting from the most stable point defects, was developed in order to identify the rate-limiting step controlling the net diffusion rate in each crystallographic direction. The uranium self-diffusivity tensor was calculated by combining the defect formation energies, entropies, migration barriers and attempt frequencies. The fastest diffusion rate was determined to be a vacancy mechanism in the z crystallographic direction. The predicted uranium self-diffusivity for this mechanism agrees well with availablemore » experimental data. Finally, the diffusion mechanisms and rates identified in this study will inform fuel performance models of swelling and gas evolution.« less

Authors:

Andersson, David Anders  ^[1];

• Search DOE PAGES for author "Andersson, David Anders"
• Search DOE PAGES for ORCID "0000-0001-5863-1372"

Matthews, Christopher  ^[1];

• Search DOE PAGES for author "Matthews, Christopher"
• Search DOE PAGES for ORCID "0000-0003-1468-1348"

Zhang, Yongfeng ^[2]; Beeler, Benjamin ^[3]

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+ Show Author Affiliations

1. Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
2. Univ. of Wisconsin, Madison, WI (United States)
3. North Carolina State University, Raleigh, NC (United States)

Publication Date:

Fri Aug 13 00:00:00 EDT 2021

Research Org.:

Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)

Sponsoring Org.:

USDOE Office of Nuclear Energy (NE), Nuclear Energy Advanced Modeling and Simulation (NEAMS); USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:

1998113

Report Number(s):

LA-UR-21-22460
Journal ID: ISSN 0022-3115; TRN: US2405354

Grant/Contract Number:  

89233218CNA000001

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Nuclear Materials

Additional Journal Information:

Journal Volume: 557; Journal ID: ISSN 0022-3115

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS; nuclear fuel; Uranium; DFT; diffusion