Abstract
The interaction of actinides and actinide alloys such as the δ-stabilized Pu-Ga alloy with iron is of interest to understand the impurity effects on phase stability. A newly developed and self-consistent CALPHAD thermodynamic database is presented which covers the elements: Pu, U, Fe, Ga across their whole composition and temperature ranges. The phase diagram and thermodynamic properties of plutonium-iron (Pu-Fe) and uranium-iron (U-Fe) systems are successfully reassessed, with emphasis on the actinide rich side. Density functional theory (DFT) calculations are performed to validate the stability of the stoichiometric (Pu,U)6Fe and (Pu,U)Fe2 compounds by computing their formation enthalpies. These data are combined to construct the Pu-U-Fe ternary phase diagram. The thermodynamic assessment of Fe-Ga is presented for the first time and application to the quaternary Pu-U-Fe-Ga system is discussed.
Highlights
The interest in actinide elements is due to their complex physics and extends across many nuclear applications; plutonium and uranium, that are studied by various government entities, largely to focus on energy production
Preliminary thermodynamic models exist in the literature [1,2,3,4,5,6,7]: Pu-U [1], Pu-Fe [2,3], Pu-Ga [1], U-Fe [3,4], U-Ga [5,6], Fe-Ga [7]
The liquid, bcc (α-Fe, δ-Fe, ε-Pu, γ-U), fcc (γ-Fe, δ-Pu) and β-U are all treated as solution phases and are modelled as substitutional solutions yielding the following molar Gibbs energy expression for a given phase φ: Gφ m =
Summary
The interest in actinide elements is due to their complex physics and extends across many nuclear applications; plutonium and uranium, that are studied by various government entities, largely to focus on energy production. The phase stability with respect to chemical composition and temperature is paramount to understanding actinide materials behavior under normal, extended/aging and off-normal (accident) conditions. The focus lies in the effects of iron (a common impurity) on actinide (An) phase stability. Since experiments can be rather tedious and expensive for actinide systems, computational models, such as the CALPHAD method is applied. Emphasis on Pu alloys with Ga acting as δ-stabilizer (fcc phase of plutonium) and U acting as a transmutation product are studied across potential composition and temperature ranges to elucidate phase relations with Fe acting as an impurity. Except for the Fe-Ga system, the binary systems included in this study of the Pu-U-Fe-Ga system have been extensively characterized in experiment (see literature review below) and preliminary thermodynamic models exist in the literature [1,2,3,4,5,6,7]: Pu-U [1], Pu-Fe [2,3], Pu-Ga [1], U-Fe [3,4], U-Ga [5,6], Fe-Ga [7]
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