UO_(2+x)芯块预氧化工艺以及低温烧结致密化机理研究  

Pre-Oxidation Treatment and Densification Mechanism for Low Temperature Sintering of UO_(2+x) Pellets

作　　者：李锐 孙茂州 聂立红 

机构地区：[1]中科华核电技术研究院集团核燃料研发设计中心,广东深圳518026

出　　处：《核动力工程》2015年第2期46-50,共5页Nuclear Power Engineering

摘　　要：为实现二氧化铀(UO2)粉末的低温活化烧结,使用综合热分析仪对UO2粉末表面进行预氧化处理,之后结合比表面积仪、X射线衍射仪以及扫描电镜分析粉末的相变点、比表面积、物相成分以及粉末微观形貌。通过以上试验得到:空气中224.6℃加热8 h后,在UO2粉末中出现了少量U3O7,而367.0℃加热8h后,UO2粉末将转变为U3O8。使用热膨胀仪对表面预氧化粉末制备的芯块进行模拟烧结试验发现:经过预氧化处理后,UO2芯块的烧结收缩温度从1200℃降低至580℃,致密速率(ΔL/L)从1.52×10-4 K-1增加到3.08×10-4K-1。基于简化点缺陷模型以及致密化方程,阐述了预氧化处理UO2+x芯块低温烧结的机理,即:UO2+x的扩散系数由于过量氧的存在,与UO2相比呈指数级别增加,该值远大于UO2的扩散系数;而芯块致密化方程中,烧结参数A与UO2+x的扩散系数正相关,其值可表示为温度T的二次多项式的指数形式;多项式参数为:a=16.23658,b=0.04247,c=-2.18802×10-5。In this paper, for the goal of sintering the uranium dioxide pellet in low temperature, UO2 powder was surface pre-oxidation treated by thermal analyzer, then the transformation point, specific area, phase component and microstructure of powder were studied by specialized instruments. The results show that there is a little of U3O7 in uranium dioxide powders by pre-oxidation treatment at 240℃ for 8h in air, and UO2 powders will transform into U3O8 at 382℃for 8h in air. The simulation sintering of UO2＋x pellet was launched by the thermal dilatometer. Shrinkage temperature of the uranium dioxide pellets after pre-oxidation treatment decreased from 1200 ℃ to 580 ℃, and the densification rate（ΔL/L） increased also from 1.52×10-4/K to 3.08×10-4/K. The mechanism of low temperature sintering to pre-oxidation UO2＋x pellets was explained by the simplified point defect model and densification equation. The UO2＋x diffusion coefficient is much higher than that of UO2. The densification factor A is positive correlation to UO2＋x diffusion coefficient,and it could be expressed by aquadratic polynomial according to temperature T, which factor a=16.23658, b=0.04247 and c=-2.18802×10-5.

关 键 词：表面预氧化 低温烧结 二氧化铀(UO2) 超化学计量 点缺陷 致密化机理 

分 类 号：TL24[核科学技术—核燃料循环与材料] TL291