The aging properties of plutonium (Pu) metal and alloys are driven by a combination of materials composition, processing history, and self-irradiation effects. Understanding these driving forces requires a knowledge of both thermodynamic and defect properties of the material. The multiplicity of phases and the small changes in temperature, pressure, and/or stress that can induce phase changes lie at the heart of these properties. In terms of radiation damage, Pu metal represents a unique situation because of the large volume changes that accompany the phase changes. The most workable form of the metal is the fcc (δ-) phase, which in practice is stabilized by the addition of alloying elements such as Ga or Al. The thermodynamically stable phase at ambient conditions is the monoclinic (α-) phase, which, however, is 20% lower in volume than the δ phase. In stabilized Pu metal, there is an interplay between the natural swelling tendencies of fcc metals and the volume-contraction tendency of the underlying thermodynamically stable phase. This study explores the point defect properties that are necessary to model the long-term outcome of this interplay.
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