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%.%Gd2Zr2O7 is a wel 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 smal 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 cel volumes. As x was increased to 0.6, the diffraction peaks showed broadening, suggesting considerable lattice distortion. When x=1, i.e., al Gd3+ was 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 is used as the host matrix for Pu4+.
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