The effect of fission products Xe and Cs on the thermal conductivity of the U3Si2lattice: a first-principles study.

In the past decades, uranium silicide (U3Si2) as a promising accident tolerant fuel (ATF) has drawn considerable attention in the field of nuclear physics. In comparison with traditional nuclear fuel (UO2), the U3Si2has higher thermal conductivity and uranium density, thereby resulting in lower centerline temperatures and better fuel economy. However, during the nuclear fission reaction, some unexpected fission products, such as Xe and Cs, are released and form the defective states. In this study, we explore the influence of Xe and Cs on the thermal conductivity of the U3Si2lattice from 200 to 1500 K using density functional theory calculations combined with Boltzmann transport equation. Our results reveal that the lattice and electronic thermal conductivities of defective U3Si2are reduced at a constant temperature, as compared with that of ideal system, thus resulting in a decrease of the total thermal conductivity. In the case of Cs occupation at U1 site, the total thermal conductivity (4.42 W mK-1) is decreased by ∼56% at 300 K, as compared with the value of 9.99 W mK-1for ideal system. With U1 and Si sites being occupied by Xe, the total thermal conductivities (4.45 and 6.52 W mK-1) are decreased by ∼55% and 35% at 300 K, respectively. The presented results suggest that the U3Si2has potential as a promising ATF at high temperatures.

First-principles study of the stability and migration of Xe and Cs in U3Si.

In the past several years, the U3Si has been suggested as an alternative nuclear fuel for light water reactors due to its high uranium density and outstanding thermal conductivity. In order to gain fundamental insights into the behavior of fission products in U3Si, the trapping and migration behaviors of the fission products Xe and Cs in U3Si are investigated using density functional theory calculations in this work. UnderU-rich and Si-rich conditions, both the Xe and Cs atoms prefer to substitute for Si andUatoms, respectively. Besides, both Xe and Cs tend to migrate through the vacancy-mechanism. It is noticeable that Xe diffuses faster and forms Xe bubbles more easily than Cs, which is mainly caused by the weaker interaction between Xe and its surrounding atoms.

First-principles study of point defects in U3Si2: effects on the mechanical and electronic properties.

In recent years, U3Si2 has been proposed as an alternative nuclear fuel material to uranium dioxide (UO2) because of its intrinsically high uranium density and thermal conductivity. However, the operation environment in the nuclear reactor is complex and extreme, such as in-pile neutron irradiation, and thus it is necessary to explore the radiation response behavior of U3Si2 and the physical properties of its damaged states. In the present study, first-principles calculations based on density functional theory were carried out to investigate the mechanical and electronic properties of defective U3Si2. Our results showed that the defect stability in U3Si2, except its interstitial defects, is dependent on its chemical environment. When vacancy, antisite or interstitial defects are introduced into U3Si2, its elastic modulus are decreased and its ductility is enhanced. Although the presence of defects in U3Si2 does not change its metallic nature and the electron distribution in its Fermi level, their effect on the partial chemical bonding interaction is significant. This study suggests that under a radiation environment, the created defects in U3Si2 remarkably affect its mechanical and electronic properties.

First-principles study of fission products Xe and Cs behaviors in U3Si2.

In the past several decades, the U3Si2has received much attention for the development of accident tolerant fuel in light water reactors because of its superior thermal conductivity and higher uranium density. In this study, density functional theory calculations have been carried out to study the occupation and diffusion behaviors of fission products Xe and Cs in U3Si2. It is revealed that the occupation sites of Xe and Cs depend on the chemical environment, and both of Xe and Cs are favorable to substitute for U or Si sites. The diffusions of Xe and Cs in U3Si2are predicted to be via the vacancy mechanism and both of Xe and Cs form cluster easily. As compared with Cs, the Xe exhibits a smaller solubility, faster diffusion as well as stronger clustering tendency, which may cause larger bubble size for Xe than Cs under the same conditions in U3Si2. The differences in the diffusion behaviors between Xe and Cs mainly result from their different valence electronic configurations and different atomic radii.

Blind image restoration with eigen-face subspace.

Performance of conventional image restoration methods is sensitive to signal-to-noise ratios. For heavily blurred and noisy human facial images, information contained in the eigen-face subspace can be used to compensate for the lost details. The blurred image is decomposed into the eigen-face subspace and then restored with a regularized total constrained least square method. With Generalized cross-validation, a cost function is deduced to include two unknown parameters: the regularization factor and one parameter relevant to point spread function. It is shown that, in minimizing the cost function, the cost function dependence of any one unknown parameter can be separated from the other one, which means the cost function can be considered roughly, depending on single variable in an iterative algorithm. With realistic constraints on the regularized factor, a global minimum for the cost function is achieved to determine the unknown parameters. Experiments are presented to demonstrate the effectiveness and robustness of the new method.