Acta Phys. -Chim. Sin. ›› 2013, Vol. 29 ›› Issue (06): 1168-1172.doi: 10.3866/PKU.WHXB201304013

• THERMODYNAMICS, KINETICS, AND STRUCTURAL CHEMISTRY • Previous Articles     Next Articles

Synthesis and Structural Transformations of (Gd1-xCex)2Zr2O7+x: An Analogue for Pu Immobilization

ZHAO Pei-Zhu1,2, LI Lin-Yan2, XU Sheng-Ming2, ZHANG Qin1   

  1. 1 College of Mining, Guizhou University, Guiyang 550003, P. R. China;
    2 Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 10084, P. R. China
  • Received:2012-12-17 Revised:2013-03-29 Published:2013-05-17
  • Supported by:

    The project was supported by NSAF (11176014).

Abstract:

Gd2Zr2O7 is a well known host for nuclear waste immobilization because of the high neutron absorption cross section of Gd and low energy transformation between ordered pyrochlore and disordered defect-fluorite structures. Pyrochlore Gd2Zr2O7 was synthesized at relatively low temperature (compared with traditional high temperature solid-state reaction) using Gd(NO3)3·nH2O, Zr(NO3)4·nH2O as a starting material and a small amount of NaF as fluxing agent. Ce4+ was used as an analogue for Pu4+ and its immobilization behavior in Gd2Zr2O7 was studied in a series of solidified forms comprising (Gd1-xCex)2Zr2O7+x (0≤x≤0.6). Powder X-ray diffraction (XRD) data showed that the sample structure transformed from pyrochlore to defect-fluorite type with increasing x but maintained constant unit cell volumes. As x was increased to 0.6, the diffraction peaks showed broadening, suggesting considerable lattice distortion. When x=1, i.e., all Gd3+ are placed by Ce4+, the product was not Ce2Zr2O8, but a phase separated mixture of tetragonal (Zr0.88Ce0.12)O2 and an ideal fluorite (Ce0.75Zr0.25)O2. Leach rate measurements indicated that the leach rate of Gd3+, Zr4+, Ce4+ was low when x≤0.2, but increased significantly when x≥0.4. This suggests that the substitution rate of Pu4+ for Gd3+ should not be more than 40% when Gd2Zr2O7 used as the host matrix for Pu4+.

Key words: Immobilization of nuclear waste, Surrogate of Ce4+ for Pu4+, Pyrochlore structure, Defect fluorite structure, Structure transformation

MSC2000: 

  • O641