In search of θ-(Pu,Zr) in binary Pu-Zr: Thermal and microstructural analyses of Pu-30Zr alloy

JOURNAL OF NUCLEAR MATERIALS

卷:528

Article

Aitkaliyeva, Assel¹  Adkins, Cynthia A.^1,2  McKinney, Casey¹  Hirschhorn, Jacob¹  Tonks, Michael R.¹ 

[1] Univ Florida, Dept Mat Sci & Engn, 176 Rhines Hall,POB 116400, Gainesville, FL 32611 USA

[2] Idaho Natl Lab, Idaho Falls, ID 83415 USA

关键词: Plutonium-zirconium;    Metallic fuel;    Microstructure;    Phase identification;    Phase transition temperatures;   

DOI  :  10.1016/j.jnucmat.2019.151875

来源: Elsevier

【 摘 要 】

The existing Pu-Zr binary phase diagrams report the stability of the compound theta-(Pu,Zr) in the low temperature region between 300 and 0 degrees C. Furthermore, the current understanding is that theta-(Pu-Zr) is thermodynamically favored over the metastable delta-(Pu,Zr) phase. In an effort to shed light on the phases formed in Pu-Zr binary alloys and reduce uncertainties in the poorly defined boundary between the theta-(Pu,Zr), (theta+delta), delta-(Pu,Zr), and (theta+alpha-Zr) regions, Pu - 30Zr (in wt.%, equivalent 53 at.%) alloys were subjected to microstructural characterization, annealing, and differential scanning calorimetry (DSC). The results indicate that the alloy is composed of delta-(Pu,Zr) matrix, with a number of smaller, randomly distributed alpha-Zr precipitates. The phase transition temperatures (determined based on the DSC data) and phases identified in Pu - 30Zr alloys (based on crystallographic data) compare well to those predicted by the phase diagrams with the exception of the theta-(Pu-Zr) phase. Our data indicates that theta-(Pu-Zr) is metastable and can be observed only within a small temperature window (100-300 degrees C). The consecutive heating cycles remove theta-(Pu-Zr) from the system, and no traces of theta-(Pu-Zr) remain at room temperature, as evidenced by microstructural characterization. This calls for reevaluation of the binary Pu-Zr phase diagram, with particular attention paid to the existence of theta-(Pu-Zr) and its stability. (C) 2019 Elsevier B.V. All rights reserved.

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