【摘要】 铈是核反应的重要裂变元素,其氧化物CeO₂容易与UO₂燃料形成U_1-xCe_xO₂固溶体。铀铈固溶体会因为U4+发生氧化而生成(U_1-xCe_x)3O_8-δ混合氧化物。Ce在U₃O₈中的存在会改变U₃O₈母体的局域结构,影响着(U_1-xCe_x)3O_8-δ产物的物理化学性质。研究铀铈混合氧化物的局域结构,可以帮助理解处于苛刻环境中乏燃料的性状。使用共沉淀方法制备了铈掺杂的U₃O₈混合氧化物样品,即(U_1-yCe_y)3O_8-δ（y=0,0.05,0.20）,利用粉末X射线衍射（X-ray Diffraction,XRD）获取其物相信息,借助同步辐射X射线吸收精细结构（X-ray Absorption Fine Structure,XAFS）技术来获取(U_1-yCe_y)3O_8-δ中铀和铈的局域结构。结果表明:与掺杂前的U₃O₈具有C2mm空间群不同,掺入Ce后的(U_1-yCe_y)3O_8-δ转变成了与U₃O₈的P62m空间群一样的晶型,Ce的存在还导致铀的平均价态升高,层内最近邻Ce-U（Ce）的原子距离减小。更多还原

【Abstract】 [Background] Cerium is one of the important products of the mixed oxide（MOX） reaction, and CeO₂ forms U_1-xCe_xO₂ solid solution with UO₂. In the post-treatment of spent fuel, UO₂ may be oxidized to U₃O₈ resulting in an increase in spent fuel volume. The structure and volume of spent fuel are concerned with the solubility, valence and electronic structure of uranium-cerium solid solutions. [Purpose] This paper aims to study the local structure of Ce-substituted U₃O₈ by X-ray absorption fine structure（XAFS） technique. [Methods] First of all,(U_1-yCe_y)3 O_8-δ（y=0, 0.05, 0.20） mixed oxides were prepared by coprecipitation method. Then, powder X-ray diffraction（XRD） and Xray absorption fine spectroscopy（XAFS） characterizations at U L3 edge and Ce K edge have been undertaken to study the chemical changes of uranium-cerium oxides. [Results] The XRD data shows that the Ce-substituted U₃O₈ has the P62 m space group which is different with α-U₃O₈. The U L3-edge X-ray absorption near edge structure（XANES） data of Ce-substituted U₃O₈ shows a slight increase in the uranium average valance. The X-ray absorption near edge structure（EXAFS） data shows that the neighboring atoms of Ce cations are far away from those of U cations. [Conclusions] The Ce cations replaced the U site in U₃O₈, and the U₃O₈ sample was changed from the original C2 mm to P62 m space group. The lattice volume was increased and the local structure around U cation was changed by adjusting the atomic distance and increasing the valence of U.更多还原