TY - JOUR

T1 - Density functional theory calculations of self- and Xe diffusion in U3Si2

AU - Middleburgh, Simon

AU - Andersson, David

AU - Stanek, Chris

AU - Claisse, Antoine

AU - Beeler, Ben

AU - Liu, X-Y

N1 - This work was funded by the Department of Energy NuclearEnergy Advanced Modeling and Simulation program. This work was carried out in collaboration with the industry led internationalCARAT program on accident tolerant fuels. Los Alamos National Laboratory, an affirmative action/equal opportunity employer, isoperated by Triad National Security, LLC, for the National Nuclear Security Administration of the U.S. Department of Energy under Contract No. 89233218CNA000001.

PY - 2019/3

Y1 - 2019/3

N2 - Uranium silicide, U3Si2, has been proposed as an advanced nuclear fuel to be used in light water reactors (LWRs). Development of this alternative to the predominant current fuel, UO2, is motivated by enhanced accident tolerance as a result of higher thermal conductivity as well as improved fuel cycle economics through increased uranium density. In order to accurately model the fuel performance of U3Si2, the diffusion rate of point defects, which is related to self-diffusion, and of fission gas atoms must be determined. DFT calculations are used to predict the U and Si point defect concentrations, the corresponding self-diffusivities, the preferred Xe trap site and the Xe diffusivity. Effects of irradiation are not considered. A low defect formation energy and a high entropy for Si interstitials give rise to Si-rich non-stoichiometry at elevated temperatures. Both U and Si self-diffusion and Xe diffusion are anisotropic as a consequence of the tetragonal crystal structure of U3Si2. Si diffusion occurs by interstitial mechanisms in both the a-b plane and along the c axis, while the U c axis diffusion rate is controlled by a vacancy mechanism. Interstitial diffusion of U is very fast in the a-b plane of the U3Si2 crystal structure. Xe atoms prefer to occupy U vacancy trap sites. The highest Xe diffusion rate occurs by a vacancy mechanism in both the a-b plane and along the c axis. The diffusion rate is similar in the a-b plane and along the c axis. U and Si self-diffusion and Xe diffusion are all faster in U3Si2 than intrinsic U and Xe diffusion in conventional UO2 nuclear fuel.

AB - Uranium silicide, U3Si2, has been proposed as an advanced nuclear fuel to be used in light water reactors (LWRs). Development of this alternative to the predominant current fuel, UO2, is motivated by enhanced accident tolerance as a result of higher thermal conductivity as well as improved fuel cycle economics through increased uranium density. In order to accurately model the fuel performance of U3Si2, the diffusion rate of point defects, which is related to self-diffusion, and of fission gas atoms must be determined. DFT calculations are used to predict the U and Si point defect concentrations, the corresponding self-diffusivities, the preferred Xe trap site and the Xe diffusivity. Effects of irradiation are not considered. A low defect formation energy and a high entropy for Si interstitials give rise to Si-rich non-stoichiometry at elevated temperatures. Both U and Si self-diffusion and Xe diffusion are anisotropic as a consequence of the tetragonal crystal structure of U3Si2. Si diffusion occurs by interstitial mechanisms in both the a-b plane and along the c axis, while the U c axis diffusion rate is controlled by a vacancy mechanism. Interstitial diffusion of U is very fast in the a-b plane of the U3Si2 crystal structure. Xe atoms prefer to occupy U vacancy trap sites. The highest Xe diffusion rate occurs by a vacancy mechanism in both the a-b plane and along the c axis. The diffusion rate is similar in the a-b plane and along the c axis. U and Si self-diffusion and Xe diffusion are all faster in U3Si2 than intrinsic U and Xe diffusion in conventional UO2 nuclear fuel.

U2 - 10.1016/j.jnucmat.2018.12.021

DO - 10.1016/j.jnucmat.2018.12.021

M3 - Article

VL - 515

SP - 312

EP - 325

JO - Journal of Nuclear Materials

JF - Journal of Nuclear Materials

SN - 0022-3115

ER -