包覆燃料颗粒制备的自动化控制系统设计与研制

针对高温气冷堆包覆燃料颗粒生产逐渐规模化大批量发展的趋势,原制备工艺的手动控制体系已不能适应,需发展现代化工业级别的包覆燃料颗粒制备自动化控制系统。针对TRISO型包覆燃料颗粒4层连续包覆工艺进行分析,将包覆炉系统划分为5个子系统,将整个包覆过程分解为9个操作状态,提出建立分布式控制系统（DCS）自动化控制系统的思路。根据对包覆颗粒制备工艺的严格要求提出了控制系统设计原则,包括连锁控制、安全可靠、集成规范、实用易用、开放和易更新原则,并在具体建设过程中实现了这些原则要求,建立起一套完整的包覆燃料颗粒制备工艺自动化控制系统。该系统在我国高温气冷堆示范工程项目辐照样品的生产中投入运行,经实践检验,证明该系统可较好地实现包覆燃料颗粒制备工艺控制,满足工厂规模的生产要求。     

包覆燃料颗粒及应用

介绍了包覆燃料颗粒技术及包覆燃料颗粒的结构和制备过程, 探讨了包覆燃料颗粒及其技术的潜在应用方向.     

HTGR包覆燃料颗粒碳化硅层细晶化研究

高温气冷堆(HTGR)是能适应未来能源市场的第四代先进核反应堆堆型之一,其固有安全性的第一道保障是使用的TRISO型包覆燃料颗粒。在TRISO型燃料颗粒4层包覆结构中,SiC包覆层是承受包覆燃料颗粒内压和阻挡裂变产物释放的关键层,制备高质量SiC包覆层是核燃料领域中的重大问题和关键技术之一。本文介绍高温气冷堆燃料颗粒的基本结构,详述制备SiC包覆层的流化床-化学气相沉积过程,提出SiC层细晶化这一研究方向,并系统阐述包覆燃料颗粒SiC包覆层细晶化的优势。在细晶化SiC材料制备方法方面,系统分析SiC粉体、陶瓷、薄膜和厚膜材料的研究现状,并结合本实验室前期研究成果提出制备细晶SiC包覆层的可行制备策略。     

碳化硅基新型包覆燃料颗粒的设计及制备

TRISO型包覆燃料颗粒可将核裂变产生的气体、固体裂变产物束缚在燃料颗粒内部,是高温气冷堆安全性的重要保障。为满足未来超高温气冷堆在更高温度及更高燃耗条件下对燃料元件的要求,需对传统TRISO颗粒进行优化和改进。基于包覆颗粒的破损机制,设计了两种SiC基新型包覆颗粒,一种采用疏松SiC层替代疏松热解炭层,包覆层由内而外依次为疏松SiC层、内致密热解炭层、致密SiC层、外致密热解炭层;另一种为全SiC包覆结构,包覆层由内而外依次为内层疏松SiC层、SiC过渡层、外层致密SiC层。根据结构设计,采用流化床化学气相沉积法实验探索了疏松SiC的形成机制及包覆工艺条件,并利用SEM、XRD等进行材料分析,最终成功实现了两种新型包覆颗粒的大规模制备。更进一步,提出了全SiC基燃料元件的概念,并制备了球形和柱形全SiC基模拟燃料元件。     

10 MW高温气冷堆首次装料的包覆燃料颗粒研制

10 MW高温气冷堆采用全陶瓷TRISO型包覆颗粒燃料元件.TRISO型包覆燃料颗粒由燃料核芯、疏松热解炭层、内致密热解炭层、碳化硅层和外致密热解炭层组成.本工作研究用于生产包覆燃料颗料的具有多气体入口的新型喷动流化床和4层连续包覆工艺.采用化学气相沉积方法在150 mm直径流化床沉积炉中生产出10 MW高温气冷堆的包覆燃料颗粒.用扫描电镜观察研究了包覆燃料颗粒的微观结构.包覆燃料颗粒的制造破损率为3.4×10-6.包覆燃料颗粒的辐照考验结果(包覆燃料颗粒的裂变产物85Krm释放率为10-6)表明,包覆燃料颗粒的性能可以满足我国10 MW高温气冷堆的设计要求.     

高温堆嬗变Pu燃料元件的制备

介绍了清华大学在制备高温气冷堆嬗变Pu惰性元件方面的研究进展.分别采用溶胶凝胶工艺和注凝成型工艺制备ZrO2陶瓷微球作为基体,经过低温烧结获得多孔微球;用U代替Pu进行浸渍后,再经过高温烧结获得致密的陶瓷微球;基体中的U含最基本稳定在10%左右.采用与10MW高温气冷堆燃料元件包覆颗粒相同的制备工艺,在ZrO2/U复合微球表面依次沉积疏松热解炭、致密热解炭、SiC和外致密热解炭,制备出包覆型嬗变燃料颗粒.     

高温堆燃料元件研制(英文)

我国10MW高温试验模块堆采用球形燃料元件,这种燃料元件由包覆燃料颗粒弥散在石墨基体里的燃料区和由不含燃料的同样基体材料外壳组成,燃料区和无燃料区之间没有物理上的分界面。用修改了的溶胶凝胶工艺制备燃料核芯,该工艺兼有内、外凝胶工艺的优点,包覆燃料颗粒采用TRISO结构。实验室产品的冷态性能和文献资料上发表的国际同类产品的相当,初步辐射结果良好;用化学提纯工艺制出了核纯天然石墨粉;用准等静压的方法制造球形燃料元件,性能指标达到了设计要求;建立并发展出高温堆燃料研究和发展所需的常规的及非常规的性能测试方法,满足了实验研究的需要。     

高温堆燃料元件研制

我国10MW高温试验模块堆采用球形燃料元件,这种燃料元件由包覆燃料颗粒弥散在石墨基体里的燃料区和由不含燃料的同样基体材料外壳组成,燃料区和无燃料区之间没有物理上的分界面。用修改了的溶胶凝胶工艺制备燃料核芯,该工艺兼有内、外凝胶工艺的优点,包覆燃料颗粒采用TRISO结构。实验室产品的冷态性能和文献资料上发表的国际同类产品的相当,初步辐射结果良好;用化学提纯工艺制出了核纯天然石墨粉;用准等静压的方法制造球形燃料元件,性能指标达到了设计要求;建立并发展出高温堆燃料研究和发展所需的常规的及非常规的性能测试方法,满足了实验研究的需要。     

10MW高温气冷堆包覆燃料颗粒的研制

我国10MW高温气冷堆采用全陶瓷型包覆颗粒球形燃料元件。TRISO型包覆燃料颗粒由燃料核芯、疏松热解碳层、内致密热解碳层、碳化硅层和外致密热解碳层组成。采用丙烯和乙炔混合气体制备致密热解碳层以及四层连续包覆的新工艺,开展生产工艺条件试验,系统地研究了生产工艺和性能之间的关系,摸索出最佳生产工艺条件。用化学气相沉积方法在150mm流化床沉积炉系统中批量生产出TRISO型包覆燃料颗粒。用扫描电镜观察分析了包覆燃料颗粒的微观结构,包覆燃料颗粒的制造破损率为3.4×10-6,冷态性能达到我国10MW高温气冷堆设计要求。包覆燃料颗粒辐照考验结果(放射性裂变产物释放率R/B为1×10-6左右)表明,包覆燃料颗粒的质量可以满足10MW高温气冷堆安全运行的要求。     

高温气冷堆燃料颗粒SiC包覆层性质研究

高温气冷堆（HTGR）燃料颗粒中的SiC包覆层是阻挡裂变产物释放最为关键的一层。本文采用XRD、Raman光谱以及SEM等方法对不同温度下在大内径喷射流化床内通过化学气相沉积法制备的燃料颗粒SiC包覆层进行微观结构分析,研究SiC包覆层在不同制备条件下的微观结构、成分以及密度变化的影响因素。结果发现,在实验设定的MTS（三氯硅烷）浓度范围内,在1 520～1 600 ℃之间均可制备出C、Si等杂质不明显的β-SiC包覆层,密度略有差异。通过微观结构分析发现,SiC包覆层密度的变小主要是由包覆层内微孔引起,且此微孔在包覆层内呈线性分布,同时基本位于某一相同的沉积表面,因此,微孔的生成与颗粒流化状态密切相关。可见,改善流化质量应是下一步工艺改进的主要方向。     

UO2燃料颗粒涂层工艺

本文简述了UO_2燃料的涂层工艺和涂层原理,评价了某些涂层设备,讨论了涂层工艺参数(涂层温度、进料参数、涂层时间等)对涂层过程及结果的影响,简单介绍了涂层产品质量的检验方法。     

Improvements in Quality of As-Manufactured Fuels for High-Temperature Gas-Cooled Reactors

The mechanisms of coating failure of the fuel particles for the high-temperature gas-cooled reactors during coating and compaction processes of the fuel fabrication were studied to determine a way to reduce the defective particle fraction of the as-manufactured fuels. Through the observation of the defective particles, it was found that the coating failure during the coating process was mainly caused by the strong mechanical shocks to the particles given by violent particle fluidization in the coater and by unloading and loading of the particles. The coating failure during the compaction process was probably related to the direct contact with neighboring particles in the fuel compacts. The coating process was improved by optimizing the mode of the particle fluidization and by developing the process without unloading and loading of the particles at intermediate coating process. The compaction process was improved by optimizing the combination of the pressing temperature and the pressing speed of the overcoated particles. Through these modifications of the fabrication process, the quality of the as-manufactured fuel compacts was improved outstandingly.     

Fabrication of uniform ZrC coating layer for the coated fuel particle of the very high temperature reactor

Fuel for the very high temperature reactor is required to be used under severer irradiation conditions and higher operational reactor temperatures than those of present high temperature gas cooled reactors. Japan Atomic Energy Agency has developed zirconium carbide (ZrC)-coated fuel particles previously in laboratory scale which are expected to maintain their integrity at higher temperatures and burnup conditions than conventional silicon carbide-coated fuel particles. As one of the important R&D items, ZrC coating process development has been started in the year 2004 to determine the coating conditions to fabricate uniform structure of ZrC layers by using a new large-scale coater up to 0.2 kg batch. It was thought that excess carbon formed in the ZrC layer under the oscillation of coating temperature would cause non-uniformity of the ZrC layer. Finally, uniform ZrC coating layer has been fabricated successfully by adjusting the time constant of the coater and keeping the coating temperature at around 1400 °C.     

Development of a suppression method for deposition of radioactive cobalt after chemical decontamination: (III) the suppression mechanism with preoxidized ferrite film for deposition of radioactive cobalt

The Hitachi ferrite coating film process (Hi-F) has been developed to lower recontamination after chemical decontamination. In this process, the chemical decontamination process is carried out, and a fine Fe₃O₄ coating film is formed on the surface of stainless steel piping in an aqueous solution. In order to improve the suppression of ⁶⁰Co deposition further, we combined the original Hi-F with a preoxidation step. We found the deposited amount of ⁶⁰Co with preoxidized Hi-F coating film (OHi-FC) was 1/10 of that for non-coated specimens. In this study, we investigated the suppression mechanism of ⁶⁰Co for the OHi-FC. The composition of OHi-FC was changed from Fe₃O₄ to Fe₂O₃ and then the crystals in the OHi-FC grew three times larger than those of the original Hi-F coating film. Consequently the corrosion amount of the stainless steel base metal was reduced by getting larger grains in the coating film. Because ⁶⁰Co was incorporated into the corrosion oxide, the suppression effect of ⁶⁰Co deposition by preoxidation was attributed to the suppression of the formation of the corrosion oxide by the OHi-FC.     

Characterization of Chemical Densified Coating as Tritium Permeation Barrier

In a fusion blanket design, ceramic coating on structural materials has been considered to be used as a tritium permeation barrier. The Chemical Densified Coating (CDC) method has some advantage compared with another coating method. This method is capable to form densified coating on either the outer or the inner surface of a tube or a container. This process temperature is low (450°C). The fabrication technique of Cr₂O₃-SiO₂ coating had been developed using CDC method. However, Cr₂O₃-SiO₂ coating had open pores in the coating. For filling open pores, the densification treatment by CrPO₄ was examined. In this study, the verification of open pores, the thermal shock resistivity, the adhesion strength and the deuterium permeability were evaluated and compared with Cr₂O₃-SiO₂ (Type 1) coating and Cr₂O₃-SiO₂ including CrPO₄ (Type 2) coating. From these results, it was confirmed that Type 2 coating had a good adhesion property, and permeation reduction factor of SS316 with Cr₂O₃-SiO₂ including CrPO₄ coating reached about 1,000 at 600°C.     

气态光源涂覆工艺中涂粉配方的优化

气态涂层光源是一种自激发光源,是利用放射性同位素发出的带电粒子激发荧光物质而发光的同位素照明装置。气态光源具有无需维护、无需外加电源,使用时不受温度、湿度、海拔高度以及使用技术影响的优点,应用广泛。荧光粉涂覆工艺是制备气态光源的关键技术之一。本研究采用单一变量的方法,通过改变荧光粉、粘结剂和固化剂等成分的比例选择更优的涂粉配方。阴极射线发光测量系统及扫描电镜结果表明,配方各成分含量分别为粘结剂PEO7.0～7.5 mL、荧光粉13～16 g、去离子水4.3 mL、添加剂0.45 mL和固化剂为7.3%～7.5%时涂覆效果较佳。     

Corrosion behavior of heat-treated Fe-Al coated steel in lead-bismuth eutectic under loading

A protective surface alloy coating on steel surfaces can prevent steels from the heavy LBE corrosion in the LBE cooled reactor. Especially, Fe-Al alloy coating on a steel surface is effective for corrosion resistance in LBE due to the self-healing of a thin and stable Al oxide layer on the surface of the coating layer. In order to investigate the utility of the coating layer under the stress due to the hydrodynamic and thermal stress induced in the practical system. The Fe-Al coated 316SS, which was heat-treated after the coating process, was immersed in the stagnant LBE at 650 °C for 250 h with loading to investigate the corrosion behavior of the specimen with the bending stress. The Fe-Al coating layer was not corroded because of the protection by Al oxide scale which was formed on the surface of the coating layer and the interface between the coating and the matrix during the heat treatment process. The coating layer cracked elastically. The LBE penetrated into the cracks and corroded the 316SS matrix and the pre-coating layer. The matrix exhibited the dissolution corrosion caused by the preferential dissolution of Ni and the oxidation forming the Fe oxide and Cr oxide. The coating layer is effective to reduce the surface of the matrix to be corroded by LBE, and can moderate the corrosion of the depth direction.     

Determination of elastic modulus and residual stress of plasma-sprayed tungsten coating on steel substrate

Plasma-sprayed tungsten, which is a candidate material for the first wall armour, shows a porous, heterogeneous microstructure. Due to its characteristic morphology, the properties are significantly different from those of its dense bulk material. Measurements of the elastic modulus of this coating have not been reported in the literature. In this work Young’s modulus of highly porous plasma-sprayed tungsten coatings deposited on steel (F82H) substrates was measured. For the fabrication of the coating system the vacuum plasma-spray process was applied. Measurements were performed by means of three-point and four-point bending tests. The obtained modulus values ranged from 53 to 57 GPa. These values could be confirmed by the test result of a detached coating strip, which was 54 GPa. The applied methods produced consistent results regardless of testing configurations and specimen sizes. The errors were less than 1%. Residual stress of the coating was also estimated.     

Simulation of thermal stress in Er2O3 and Al2O3 tritium penetration barriers by finite-element analysis

The physical vapor deposition method is an effective way to deposit Al2O3 and Er2O3 on 316L stainless steel substrates acting as tritium permeation barriers in a fusion reactor.The distribution of residual thermal stress is calculated both in Al2O3 and Er2O3 coating systems with planar and rough substrates using finite element analysis.The parameters influencing the thermal stress in the sputter process are analyzed,such as coating and substrate properties,temperature and Young's modulus.This work shows that the thermal stress in Al2O3 and Er2O3 coating systems exhibit a linear relationship with substrate thickness,temperature and Young's modulus.However,this relationship is inversed with coating thickness.In addition,the rough substrate surface can increase the thermal stress in the process of coating deposition.The adhesive strength between the coating and the substrate is evaluated by the shear stress.Due to the higher compressive shear stress,the Al2O3 coating has a better adhesive strength with a 316L stainless steel substrate than the Er2O3 coating.Furthermore,the analysis shows that it is a useful way to improve adhesive strength with increasing interface roughness.