二氧化铀陶瓷燃料块工艺研究进展

简述了铀及铀氧化物、二氧化铀陶瓷燃料块制备工艺的发展和应用.重点阐述了超化学计量二氧化铀芯块在微氧化气氛下低温活化烧结的最新研究进展.从理论上,提出了扩散烧结和强化烧结是二氧化铀陶瓷燃料块低温烧结的过程机理;从工艺上,提出了工艺稳定性和提高晶粒尺寸是二氧化铀陶瓷燃料块低温烧结的热点课题.展望了二氧化铀陶瓷燃料块微氧化低温烧结的工业应用前景.     

液相烧结大晶粒UO2及其烧结动力学分析

大晶粒二氧化铀(UO₂)芯块因具有低辐照肿胀、低裂变气体释放及优异的燃料包壳相互作用效应(PCI),而成为未来先进反应堆关注的候选燃料。本文采用液相烧结工艺制备大晶粒UO₂芯块，研究了液相烧结对UO₂芯块烧结性能、显微结构和烧结动力学的作用机制和影响规律。结果表明：通过添加金属铀粉形成的液相烧结可明显促进UO₂芯块的致密化速度，液相烧结UO₂芯块的烧结特征指数为2.937,烧结机理主要为晶界扩散，烧结激活能为103.00 kJ/mol,低于普通UO₂芯块的烧结激活能(110.65 kJ/mol);液相烧结UO₂芯块晶粒生长指数为2.831,晶粒生长活化能为463.97 kJ/mol,低于普通UO₂芯块晶粒生长激活能(510 kJ/mol),加入的金属铀粉形成的液相烧结可促使晶粒长大；添加金属铀粉液相烧结工艺具有不引入非铀杂质元素、加快芯块致密化速度和增大芯块晶粒尺寸的多重作用。     

UO2+x芯块低温烧结的活化机理

报道了UO2+x芯块低温烧结实验的结果.12组芯块在N2+CO2组成的部分氧化气氛下于立式钼丝炉中低温烧结.UO2芯块要获得密度为10.41g/cm3(94.98％理论密度)需在氢气氛中于2073～2273K下烧结,而UO2+x芯块实现该密度的烧结温度可降低400K以上.建立了超氧化铀缺陷模型来研究低温烧结的活化机理.研究发现铀离子扩散系数与气氛中氧分压或是UO2+x中x成正比.利用铀离子的扩散系数,可预测UO2+x芯块在1073、1273、1473和1673K温度下的烧结密度；还可算出x=0.04时,UO2+x芯块在部分氧化气氛下的理论烧成温度.计算所得烧结密度和烧成温度与实验结果符合得很好.     

粉末表面氧化对二氧化铀芯块烧结性能的影响

用SEM、XRD、BET和DSC TG、热膨胀仪等观察了UO₂粉末的形貌结构并研究粉末氧化前后的烧结性能,分析了UO₂粉末表面预氧化对二氧化铀芯块烧结性能的影响。结果表明,240℃×8 h是UO₂粉末预氧化表面改性的最佳工艺;粉末改性后表层为UO_2+x和少量U₃0₇,改性粉末压坯在氩气气氛中开始发生收缩的温度降低了530-600℃,平均线收缩率提高了1倍;在本氩气保护条件下,热膨胀试验后芯块的密度从8.52 g/cm³提高到9.44 g/cm³。采用本改性粉末,在1300℃×5 h/N2+5%CO₂-1500℃×1 h/H₂批试烧结,其密度达10.26 g/cm³,O/U比为2.013。     

凝胶注模制备环形二氧化铀芯块工艺研究

环形二氧化铀芯块在提高反应堆功率密度上有诸多优势,本实验以N-羟甲基丙烯酰胺为凝胶体系,对环形UO_2燃料芯块进行了凝胶注模成型,研究了该体系下pH值、固相含量对浆料粘度的影响规律,同时研究了单体/交联剂比例、预混液/引发剂比例对料浆凝胶固化的影响。在此基础上,进行了环形UO_2燃料芯块注模成型,并对生坯芯块进行了干燥与烧结。结果表明:pH=9.5、固相含量为58vol%时,能制备出高固相含量、低粘度的UO_2陶瓷浆料;当单体/交联剂质量比为15/1、预混液/引发剂体积比为100/2时,凝胶固化效果最好。本工作还制备了壁厚分别为2.5 mm和1.5 mm的环形芯块生坯,其烧结后的壁厚分别为2.0 mm和1.2 mm左右;烧结密度、晶粒尺寸等指标满足技术要求。     

液相烧结SiC陶瓷的研究进展

综述了液相烧结SiC陶瓷的烧结添加剂体系、烧结工艺、烧结机理,并简要介绍了几种新的烧结方法.介绍了液相烧结SiC的微观结构和性能,讨论了SiC-YAG及SiC-Al-BC烧结体系的特点和烧结体性能,简述了利用SPS、微波烧结等新方法制备液相烧结SiC陶瓷的机理及研究进展.     

高温气冷堆控制棒B4C芯块的研制

阐述了用电弧炉碳热还原法制备核级B4C粉末、经热压烧结制备高温气冷堆控制棒B4C芯块的研制过程，研究了添加剂对制备B4C芯块的影响。     

二氧化铀芯块低温烧结机理的研究

基于PDM(point defect model),研究了UO2 x在微氧化性气氛下低温烧结的机理.理论讨论和试验验证了UO2低温烧结时铀离子的体扩散系数、低温烧结温度和致密化动力学方程.结果表明,在UO2中掺入多余氧可使铀离子的扩散激活能降低约3.0eV,铀离子的扩散激系数DUx∝x2,二氧化铀低温烧结的理论温度约为1089～1151℃,采用UO2 x坯块是实现低温烧结的必要条件.本模型理论计算的结果与试验数据符合较好,能很好地表征缺陷浓度随气氛变化的特点.     

脉冲电流烧结技术及其在氮化铝透明陶瓷烧结中的应用

脉冲电流烧结(Pulse electric current sintering,PECS)是近十年发展起来的一种特殊的快速烧结技术.介绍了脉冲电流烧结的特征、研究现状及其在氮化铝透明陶瓷烧结中的应用.     

碳化硅陶瓷的活化烧结与烧结助剂

综述了作为碳化硅陶瓷烧结助剂的热力学条件及液相烧结的有效条件,介绍了碳化硅陶瓷烧结助剂的研究进展.     

Thermal and mechanical properties of uranium nitride prepared by SPS technique

Nitride fuel is a promising nuclear fuel in fast breeder reactor (FBR) or accelerator-driven subcritical reactor (ADSR) system. In this study, high-density UN pellets were prepared by Spark plasma sintering (SPS) technique. The sample density strongly depended on the sintering temperature and pressure, and the pellets with 90% of theoretical density were easily obtained with low sintering temperature and short sintering time without any milling process. The grain size and pore size were much smaller compared with those for samples prepared by conventional sintering process. Despite of the small grain size, the thermal conductivity remains the high value. The SPS process permits easy densification of nitrides without any deterioration of thermal and mechanical properties, considered to be suitable as a preparation method of nitride fuels.     

基于立体光刻的弥散型核燃料的制备

弥散型核燃料芯块中的核素分布强烈的影响反应堆的行为.本研究首次提出将立体光刻快速成型技术应用于氧化镁-氧化钚弥散型陶瓷核燃料的制备,显著地提高了核燃料微球在芯块中的分布均匀性.其中氧化镁作为基体起着结构材料作用,维持芯块的形状并提高核燃料芯块的导热率.文章详细探究了氧化镁粒径对浆料粘度、切片厚度,以及后处理过程对芯块的影响.最终芯块中的氧化镁弥散介质的密度达到3.15 g/cm3(理论密度的88.1％).最终芯块的剖面图表明核燃料微球在芯块中的分布高度均匀,本研究提供了一种制备核素分布高度均匀的弥散型核燃料芯块的新方法.     

Synthesis of High-Density Pellets of Uranium Dioxide by Spark Plasma Sintering in Dies of Different Types

A procedure for electric pulse consolidation of commercial UO₂ powders of various ceramic grades into high-density fuel pellets using dies of various types was studied. The influence of the parameters of spark plasma sintering (SPS) on the chemical composition of the initial powders and quality of ready UO₂ pellets was examined. The main advantages and drawbacks of the SPS process for consolidation of UO₂ powder in standard graphite dies were revealed. A novel alternative procedure for SPS of UO₂-based fuel pellets in Mo-based dies was suggested. High quality of the pellets (density 97.5–98.4% of theoretical, no C impurity, mean grain size no more than 3 μm) and mild sintering conditions (1100°С, 141.5 MPa, 25 min) make the process highly promising. The results obtained are of interest for the development and possible implementation of an industrial SPS process for production of ceramic nuclear fuel.     

SiC陶瓷基片的烧结工艺与SiC_p/Al复合材料的制备方法

概述了电子封装基片材料的基本性能要求;讨论了SiC陶瓷基片常用的4种烧结工艺,即常压烧结、热压烧结、反应烧结和放电等离子烧结;介绍了SiCp/Al复合材料的制备方法,即搅拌铸造法、无压渗透法、喷射沉积法、粉末冶金法;据此进一步提出了SiC陶瓷基片材料的发展方向。     

熔融石英陶瓷的研究及应用进展

主要介绍了石英陶瓷的成型技术、烧结方法、添加剂对熔融石英陶瓷烧结性能的影响及其应用现状.振动压力注浆成型是在传统的注浆工艺基础上改进而成的,能显著提高陶瓷坯体的强度,而凝胶注模成型技术则非常适用于成型复杂形状的陶瓷制品,二者均为石英陶瓷比较成熟的成型技术;在烧结过程中升温速率和冷却速率是影响石英陶瓷性能的关键因素,通过添加B4C和Si3N4能显著提高石英陶瓷制品的致密度;目前石英陶瓷已广泛应用于冶金、玻璃、钢铁、航空等诸多领域.     

Nondestructive characterisation of MOX fuel rods using gamma autoradiography (GAR)

During the fabrication of mixed uranium-plutonium oxide (MOX) fuel rods, two important characteristics to be checked in as-fabricated fuel pins are plutonium enrichment and plutonium dioxide agglomerates. The mixed oxide fuel pellets are made via mechanical mixing of uranium dioxide and plutonium dioxide powders by cold compaction and sintering. The chance of loading a wrong Pu enrichment pellet and having pellets with plutonium dioxide agglomerates in a fuel pin cannot be ruled out. A simple nondestructive evaluation technique is felt necessary to ensure at the last stage (in the welded pins) to check these two characteristics. During the fabrication of MOX fuel rods for Boiling Water Reactors at Advanced Fuel Fabrication Facility of BARC at Tarapur, Gamma-auto-radiography was successfully used to evaluate composition of MOX pellets and to detect presence of PuO₂ agglomerates in the peripheral region. The fuel pins are allowed to be in contact with industrial X-ray films loaded in cassettes for a long time and the processed films are carefully evaluated. Experiments were made to standardise the conditions for distinguishing fuel pellets of different composition by gamma-auto-radio-graphy of fuel pins loaded with pellets of different composition. Gamma-auto-radiography of fuel pins containing agglomerates of different sizes was also carried out. This paper describes the experimental details of the technique, results obtained and compare with other nondestructive evaluation techniques available.     

先进陶瓷材料固相烧结理论研究进展

系统介绍了陶瓷材料固相烧结理论的历史和研究进展,综述了用来描述烧结前期、中期和后期的烧结理论和烧结模型.目前烧结理论大多局限于烧结全程的某一阶段,且只研究某一种扩散机制起主导作用,多数理论烧结模型不能完全反映真实烧结参数,烧结单元模型的定量描述不够完善,缺乏描述烧结全程的烧结模型,且大多研究局限于基础研究,如物质的传输机制、致密化过程、气孔和晶粒生长机制.因此,建立多种扩散机制耦合作用的全期烧结模型,进一步研究烧结动力学,用计算机模拟烧结的真实条件,建立能定量描述的烧结模型,是未来烧结理论研究的方向.     

Manganous-zinc ferrites synthesized out of MnO

Manganous-zinc ferrites are best prepared directly from MnO and can be conveniently pressed with non-volatilizable binders such as polyvinyl alcohol which however can be burnt out without oxidizing the Mn²⁺ in the ferrite by sintering in a static atmosphere generated by the thermal dissociation of active ferric oxide pellets placed out of contact with the ferrite in the closed sintering unit. Such a process eliminates cracks and rejections in the sintered pieces besides giving very satisfactory and reproducible results. NCL Communication No. 3059     

陶瓷燃料电池电解质流延膜的烧结工艺及其性能研究

本文采用“三明治式多孔夹板”烧结方法制得了均匀致密的、用于燃料电池的固体电解质膜材,用SEM方法观察了膜材的微观形貌,还用复数阻抗频谱仪对烧结膜材的电导性能进行了测定,实验结果表明,所采用的烧结工艺能有效解决单层厚膜烧结中易出现的起翘与开裂问题,所制得的膜材的电性能亦能满足陶瓷燃料电池的要求．