Phase diagrams constructed for the Pu-Zr binary system report the existence of θ-(Pu,Zr), δ-(Pu,Zr), γ-Pu, α-Pu, β-Pu, and ζ-Pu28Zr phases in Pu-enriched region, when Pu concentrations exceed 75 at.% (equivalent to 89 wt% Pu). The compound θ-(Pu,Zr) has been said to occur at about 20 at.% Zr, but the regions for θ-(Pu,Zr) on the Pu-rich side have not been well defined. In an effort to understand the phases formed in Pu-Zr binary alloys and define the boundary between θ-(Pu,Zr), (θ+δ), and δ-(Pu,Zr) regions, Pu-10Zr (in wt.%, equivalent 23 at.%) alloys were scrutinized in this contribution. This manuscript details microstructural characterization and phase identification results obtained using electron microscopy-based techniques for a Pu-10Zr alloy before and after annealing at 550 °C. In contradiction with predicted phase diagrams, no θ-(Pu,Zr) was detected in any of the examined specimens. The phases present in as-cast fuel included a δ-(Pu,Zr) matrix with a number of smaller, randomly distributed α-Zr, ZrO2, Zr3O, PuO, and κ-PuZr2 inclusions. Heat treatment annealed out the intermetallic κ-PuZr2 phase and resulted in formation of small δ′-Pu and β-Pu inclusions. Similar to the as-cast alloys, the matrix of the annealed alloys was consistent with δ-(Pu,Zr) phase and contained small α-Zr, ZrO2, and PuO2 inclusions. Two different microscopy-based techniques were used for phase identification, but neither identified any θ-(Pu,Zr) phase. Differential scanning calorimetry was then used to determine the phase transition temperatures and enthalpies of transition for the identified phases. While our data is similar to the existing phase diagrams, a number of discrepancies are reported that call for a careful re-examination of the Pu-Zr system. This contribution discusses different scenarios that could explain the discrepancies between obtained and historical data, and provides the most logical conclusion that could be reached based on the obtained results.
All Science Journal Classification (ASJC) codes
- Nuclear and High Energy Physics
- Materials Science(all)
- Nuclear Energy and Engineering