物理化学学报 >> 2013, Vol. 29 >> Issue (06): 1168-1172.doi: 10.3866/PKU.WHXB201304013

热力学,动力学和结构化学 上一篇    下一篇

Ce4+替代Pu4+的模拟固化体(Gd1-xCex)2Zr2O7+x的合成及结构演变

赵培柱1,2, 李林艳2, 徐盛明2, 张覃1   

  1. 1 贵州大学矿业学院, 贵阳 550003;
    2 清华大学核能与新能源技术研究院, 北京 100084
  • 收稿日期:2012-12-17 修回日期:2013-03-29 发布日期:2013-05-17
  • 通讯作者: 李林艳 E-mail:lilinyan@tsinghua.edu.cn
  • 基金资助:

    国家自然科学基金委员会和中国工程物理研究院联合基金(11176014)资助项目

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).

摘要:

Gd2Zr2O7中Gd具有很大的中子吸收截面, 其烧绿石结构-缺陷萤石结构的转变能较低, 使其成为理想的核废料固化基材. 使用硝酸盐为原料, 添加少量NaF作助熔剂, 在较低温度下(和传统高温固相反应相比), 合成了烧绿石型Gd2Zr2O7. 以Ce4+模拟Pu4+, 研究了Gd2Zr2O7对锕系核素的固化, 并合成了系列模拟固化体(Gd1-xCex)2Zr2O7+x (0≤x≤0.6). 采用粉末X射线衍射(XRD)对系列样品进行了表征. 结果表明: 随着x值的增大,样品从烧绿石结构向缺陷萤石结构转变, 且晶胞大小基本保持恒定, 但当x=0.6时, 衍射峰明显宽化, 晶格畸变比较严重, 晶格稳定性降低. 当x=1时, 即用Ce4+完全取代Gd3+进行合成, 不能得到Ce2Zr2O8, 产物发生了相分离, 为四方结构的(Zr0.88Ce0.12)O2和萤石结构的(Ce0.75Zr0.25)O2的混合物. 模拟固化体的浸出率测试表明: 当x≤0.2时, 各元素浸出率均很低, 但当x≥0.4时, 各元素的浸出率明显升高, 说明以Gd2Zr2O7作为固化Pu4+的基材, Pu4+掺入量不宜高于40%.

关键词: 核废料固化, Ce4+替代Pu4+, 烧绿石结构, 缺陷萤石结构, 结构演变

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