An investigation of the thermal stability of NdxYyZr1−x−yO2−δ inert matrix fuel materials

• Published in: Journal of alloys and compounds Vol. 635; pp. 245 - 255
• Main Authors: Hayes, John R., Grosvenor, Andrew P., Saoudi, Mouna
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 25-06-2015
• Subjects: Fuel cycle; Inert matrix; Nuclear fuel; Structural characterization; X-ray absorption spectroscopy; Yttria-stabilized zirconia; Inert matrix; Nuclear fuel; X-ray absorption spectroscopy; Structural characterization; Fuel cycle; Yttria-stabilized zirconia
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2015.02.022

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•Yttria-stabilized zirconia (YSZ) has been proposed for use as inert matrix fuel.•Nd was used to simulate effects of Am incorporation on the YSZ structure.•The structural stability of Nd–YSZ was studied over a range of temperatures.•The effect of annealing was characterized by XRD, SEM, EDS, XAS.•This study shows that the addition of Y3+ stabilized the Nd–YSZ system.
An important step in achieving a closed uranium fuel cycle is to develop new inert matrix fuel (IMF) materials for use in the burn-up of transuranic species (TRU; i.e., Pu, Np, Am, Cm). Cubic fluorite zirconia (ZrO2) has ideal properties for use in IMF applications, but it is not stable at room temperature and must be stabilized through the addition of small amounts of dopants such as Y. While Y-substituted zirconia (YSZ) has been extensively studied, relatively little work has been done to investigate how the addition of an actinide to the YSZ system affects the properties of these materials. To this end, the long-range and local structures of a series of NdxYyZr1−x−yO2−δ compounds (Nd was used as a surrogate for Am) were studied using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray absorption spectroscopy (XAS) at the Zr K-, Zr L3-, Y K-, and Nd L3-edges. The thermal stability of Nd–YSZ materials was also investigated by annealing the materials at temperatures ranging between 600 and 1400°C. These studies showed that the thermal stability of the NdxYyZr1−x−yO2−δ system was improved by the addition of small amounts of Y (i.e. ⩾5at.%) to the system. Additionally, the XAS results showed that the local structure around Zr remained relatively constant; only changes in the second coordination shell were observed when the materials were annealed. These results strongly suggest that the addition of Y can significantly improve the thermal stability of zirconia-based IMFs. This study has also confirmed the importance and value of using advanced characterization techniques that are sensitive to the local structures of a material (i.e., XAS).