外胶凝法制备Th_(x)Zr_(1-x)O_(2)惰性基质燃料胶凝行为及微结构研究

Gelation behavior and microstructure of Th_(x)Zr_(1-x)O_(2)inert matrix fuel prepared by an external gelation process

惰性基质燃料(Inert Matrix Fuel,IMF)可有效转化钚和长寿命次锕系核素,可以防止核武器扩散和提高乏燃料管理能力,是近年来的一个研究热点。溶胶凝胶法具有产品元素分布均匀、湿法操作流程不易产生放射性粉尘等优点,因此,在研究中被用于制备锆基IMF。采用外胶凝工艺制备Th_(x)Zr_(1-x)O_(2)惰性基质燃料,以溶黏度为主要的胶凝指征,研究了不同金属离子浓度、不同温度下溶胶黏度随c(NH_(4)^(+))/c(NO_(3)^(-))的变化规律,归纳了不同工艺参数条件下的溶胶胶凝行为类型,绘制了胶凝化场图,可为成功制备相应的凝胶湿球提供量化依据。采用X射线衍射(X-ray Diffraction,XRD)研究了经过不同温度热处理之后的核芯结构,结果表明:经过1350℃烧结退火后的微球生成了两相金属氧化物相,ZrO2在氧化钍基底中未生成固溶体,X射线成像结果表明,微球具有良好的球形度且内部没有裂纹。扫描式电子显微镜(Scanning Electron Microscope,SEM)和能量弥散X射线谱(Energy Dispersive Spectrometer,EDS)结果表明,微球内部孔洞致密且元素分布达到分子级均匀。

[Background]Inert matrix fuel(IMF)can efficiently convert plutonium and long-lived minor actinides used for preventing the proliferation of nuclear weapons and improving spent fuel disposal,hence has been becoming a hot research topic in recent years.The sol-gel method has the advantage of uniform elemental distribution of the products and the wet operation process is less likely to produce radioactive dust,therefore,it has been used to prepare zirconium-based IMF in the research.[Purpose]This study aims to prepare a colloidal solution with good dispersive properties and to obtain IMF microspheres with good sphericity,uniform size,and homogeneous elemental distribution.[Methods]First of all,Th_(x)Zr_(1-x)O_(2)inert matrix fuel was prepared by an external gelation process,and the sol-gel viscosity was used as the main gelation index.Then,the variation tendency of sol viscosity with c(NH_(4)^(+))/c(NO_(3)^(−))was investigated for different metal ions concentrations and different temperatures.Finally,the statistical distributions of colloidal particle sizes were obtained for different metal ions and reaction temperatures by laser particle sizing tests,and the X-ray diffraction(XRD)was used to study the structure of IMF after heat treatment at different temperatures.[Results]The results showed that the complex gelation parameters and properties can be categorized and quantified using gelation field diagrams.In addition,Th_(x)Zr_(1-x)O_(2)IMF kernels with uniform element distribution,good sphericity,and integral appearance were obtained by optimizing the process parameters.Zirconia showed low solubility behavior in the thorium-oxide system,leading to the generation of a biphasic structure.[Conclusions]The results of this study indicate that zirconium-based spherical IMF microspheres with good performance can be prepared by external gelation method.