铀、钍在Nd2Zr2O7烧绿石中的固化研究

为研究锕系元素铀、钍在烧绿石中的固化行为，通过喷雾热解-高温烧结成功合成了含铀、钍的系列Nd2Zr2O7烧绿石固化体，并采用XRD、SEM、EDS、Raman光谱和XPS等方法对所得固化体样品进行了表征。结果表明：铀、钍均能进入Nd2Zr2O7晶格的A位形成稳定的烧绿石结构。Th在固化体中的固溶量（摩尔分数，下同）达到40%，固化体保持较好的烧绿石单相结构；随着Th含量的增加，固化体转变为烧绿石、立方ZrO2和ThO2共存的多相陶瓷结构。U在Nd2-xUxZr2O7烧绿石中的固溶量仅为10%，固化体结构无序化明显增加；随着U含量的增加，固化体快速转变为萤石结构，铀固溶量约为20%。铀、钍在Nd2Zr2O7烧绿石固化体中固溶量存在较大差异。XPS分析发现，Th在烧绿石固化体中以+4价存在；U在固化体中以+4价和+6价存在，导致固化体A位离子的配位结构发生变化，更多氧离子进入烧绿石体系，导致体系转变为无序化萤石结构，固溶量明显下降。

Solidification of Uranium and Thorium in Nd2Zr2O7 Pyrochlore

In order to study the solidification behavior of actinides uranium in pyrochlore, a series of Nd2-xThxZr2O7 and Nd2-xUxZr2O7 samples were prepared by the sol gel spray pyrolysis high temperature sintering method. These samples were characterized by XRD, SEM, EDS, Raman and XPS. For Nd2-xThxZr2O7, the solubility of thorium is estimated up to 40%, the structure of immobilization remains single pyrochlore structure phase. Further addition of thorium in the Nd2Zr2O7 pyrochlore leads to the formation of multi phase structure with pyrochlore, ZrO2 and ThO2. The solubility of uranium in the Nd2Zr2O7 pyrochlore is found only 10%, the pyrochlore structure shows the transformation of disorder. With the increase of uranium content, the structure transforms from disordered pyrochlore to fluorite structure, the solubility of uranium in fluorite structure is estimated to about 20%. The solubility of uranium and thorium in the Nd2Zr2O7 pyrochlore shows the significant difference. Compared with Th(Ⅳ) ion, uranium exhibits +4 and +6 valence states in the immobilization. For Nd2-xUxZr2O7, more oxygen are incorporated in the lattice of pyrohlore due to the higher average valence of uranium, the coordination structure of pyrochlore is changed. The Nd2-xUxZr2O7 pyrochlore quickly transforms into the disordered fluorite structure with uranium content increasing, the solubility of uranium decreases significantly.