Abstract
As potential nuclear waste host matrices, two series of uranium-doped Nd2Zr2O7 nanoparticles were successfully synthesized using an optimized molten salt method in an air atmosphere. Our combined X-ray diffraction, Raman and X-ray absorption fine-structure (XAFS) spectroscopy studies reveal that uranium ions can precisely substitute the Nd site to form an Nd2-xUxZr2O7+δ (0 ≤ x ≤ 0.2) system and the Zr site to form an Nd2Zr2-yUyO7+δ (0 ≤ y ≤ 0.4) system without any impurity phase. With increasing U concentration, there is a phase transition from pyrochlore (Fd3m) to defect fluorite (Fm3m) structures in both series of U-doped Nd2Zr2O7. The XAFS analysis indicates that uranium exists in the form of high-valent U6+ in all samples. To balance the extra charge for substituting Nd3+ or Zr4+ by U6+, additional oxygen is introduced accompanied by a large structural distortion; however, the Nd2Zr1.6U0.4O7+δ sample with high U loading (20 mol%) still maintains a regular fluorite structure, indicating the good solubility of the Nd2Zr2O7 host for uranium. This study is, to the best of our knowledge, the first systematic study on U-incorporated Nd2Zr2O7 synthesized via the molten salt method and provides convincing evidence for the feasibility of accurately immobilizing U at specific sites.
Highlights
The disposal of actinide-rich nuclear waste is a key issue for the development of sustainable nuclear energy (Ewing, 2011; Abdou et al, 2018; Finkeldei et al, 2020; Liu et al, 2021)
Rietveld refinement of the X-ray diffraction spectroscopy (XRD) pattern demonstrates the purity of the NZO sample with a pyrochlore structure [Fig. 1(b)], and the parameters are summarized in Table S1 of the supporting information
We systematically studied the uranium solubility, crystalline phase, valence state and structural evolution in a Nd2Zr2O7 pyrochlore synthesized by a modified molten salt method
Summary
The disposal of actinide-rich nuclear waste is a key issue for the development of sustainable nuclear energy (Ewing, 2011; Abdou et al, 2018; Finkeldei et al, 2020; Liu et al, 2021). The search for high-capacity, low-cost and radiation-tolerant materials that can be used as host materials for nuclear wastes has been a major research interest for a long time. Pyrochlore oxides have received considerable attention in immobilizing actinides owing to their desirable physical-chemical properties, including their high thermal stability, high chemical durability, and strong resistance to radiation damage (Abdou et al, 2018; Fuentes et al, 2018; Finkeldei et al, 2020). Realizing the rational manipulation of the phase structure and substituting sites in zirconate pyrochlore, as well as developing low-cost and sustainable synthetic methods, remains a tremendous challenge, which has practical significance in the application of immobilizing actinides
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
