金属铀表面含氧碳化物的组成与性质

金属铀的表面极活泼,易氧化腐蚀。为降低金属铀表面的活性,人们曾尝试采用真空热氧化的办法在其表面形成所谓的一氧化铀。应用X射线光电子能谱(X-ray Photoelectron Spectroscopy,XPS)和俄歇电子能谱(Auger Electron Spectroscopy,AES)研究了金属铀真空热氧化膜及其在大气中腐蚀的产物。分析结果得到金属铀真空热氧化膜主要含有二氧化铀(UO_2)和含氧碳化铀相(UC_xO_(1-x))。采用AES相对灵敏度因子法计算出UC_xO_(1-x)相组成近似为UC_(0.41±0.04)O_(0.62±0.01)。真空热氧化膜中的含氧碳化铀相在大气中会继续氧化腐蚀并产生二氧化铀和非束缚态碳。讨论了表面含氧碳化铀相对金属铀腐蚀性能的影响,认为表面含氧碳化铀相的存在是延缓金属铀在大气气氛中腐蚀的关键因数。     

金属铀表面氧化动力学的X射线衍射研究

利用X射线衍射和Rietveld方法研究室温～150℃和300℃下金属铀表面氧化，对氧化过程中试样的表面结构以及氧化动力学进行分析。将试样表面氧化物随时间的变化作定量计算，绘制出不同温度下金属铀表面的氧化动力学曲线，对50～150℃范围内的氧化动力学数据进行拟合，获得不同温度下的氧化反应速率常数，由此得到大气环境下金属铀表面形成UO₂的活化能为46.0kJ/mol。在300℃下，氧化产物U₃O₈逐渐在UO₂上形成，其形成过程符合成核生长机理。     

金属铀环境腐蚀的表面状态研究

采用显微激光拉曼和傅立叶变换红外光谱技术,结合扫描开尔文力显微镜,在线研究了金属铀在大气环境中、一定温度范围内样品表面腐蚀的微区形貌和反应产物的变化情况。结果表明,金属铀在室温时表面微区形貌呈球形凸凹粒状不均匀分布,且在颗粒边缘和凹坑处表面电位较高,易发生点蚀。在大气环境条件下会吸附空气中的O2、H2O和CO2反应生成UO2、铀酰化物和碳酸盐等,不同温度加热,铀表面首先出现活性腐蚀亮斑,并逐渐积累长大,其主要氧化产物UO2在260℃以上开始转化为U3O8。     

采用椭偏光谱技术研究铀氧化动力学

采用椭偏技术研究了45～95 ℃和5 kPa纯氧气氛中金属铀的氧化,通过不同温度下金属铀表面氧化层厚度随时间的变化规律,得到贫铀在初始氧化阶段的表面氧化层厚度与时间的关系均呈现抛物线规律;绘制出了在不同温度下金属铀表面的氧化动力学曲线,由此得到在低于100 ℃, 5 kPa的纯氧气氛下贫铀表面形成氧化物的反应活化能为87.165 kJ/mol.     

超临界CO2处理后的金属铀表面氧化腐蚀和电化学腐蚀实验研究

采用重量法和电化学方法分别得到表面经超临界CO2处理后的铀试样在60℃、70％RH条件下的氧化动力学曲线(△m-t)和在50μg/g Cl^-溶液中的阳极极化曲线、自腐蚀电流等抗蚀评价指标。结果表明：经超临界CO2处理后，金属铀表面抗氧化腐蚀性能和抗化学介质腐蚀性能均有一定程度提高。对钝化膜提高金属铀表面抗腐蚀性能的原因进行了探讨。     

CO处理对铀在40℃和70℃潮湿空气中抗蚀性能的影响

采用增重法研究了金属铀表面经CO处理后在40℃和70℃潮湿空气中的抗蚀能力。研究结果表明，在70℃潮湿空气中，其抗蚀能力增加不明显；而在40℃环境中，金属铀表面的抗蚀能力得到明显提高，且在实验范围内其抗能力随CO剂量的增加而增强。用俄歇电子谱（AES）分析了铀试样处理前后表层的成分变化。分析结果表明，铀表面径CO处理后，其表层形成了一定厚度的富碳层，并显示该富碳层对提高铀表面抗蚀能力起着重要作用。     

金属铀表面经CO处理后的腐蚀行为研究

采用增重法和电化学方法分别研究了金属铀表面经CO处理后在40℃干燥空气中的抗氧化能力和在14mmol/L Cl^-溶液中的抗化学介质腐蚀的能力。研究结果表明：金属铀表面经CO处理后，在40℃干燥空气中的抗氧化能力增强；在14mmol/L Cl^-溶液中的抗化学介质腐蚀的能力也增强，而且在实验所用CO剂量范围内，金属铀的抗腐蚀能力随C0剂量的增加而增强。     

金属铀表面非平衡磁控溅射CrNx薄膜的XPS分析与腐蚀性能

金属铀的化学性质十分活泼,极易发生氧化腐蚀。为改善基体的抗腐蚀性能,采用非平衡磁控溅射离子镀技术在金属铀表面制备CrN_x薄膜。采用X射线衍射和X射线光电子能谱研究薄膜表面的物相结构和元素成分分布,采用极化曲线研究薄膜的抗腐蚀性能。结果表明,CrN_x薄膜具有较好的致密性和抗腐蚀性能。当氮分压较小时,生成的薄膜为Cr+CrN+Cr₂N混合相。在金属铀表面制备1层CrN_x薄膜后,其腐蚀电位增大约465 mV,腐蚀电流密度明显降低,有效改善了贫铀表面的抗腐蚀性能。     

用X射线光电子能谱研究CO_2在金属铀表面的初期氧化行为

采用X射线光电子能谱技术(XPS)原位研究CO_2气体与清洁金属铀表面的相互作用机理。贫化铀试样在XPS分析真空室中经氩离子枪溅射蚀刻得到清洁金属铀表面。分别观测U4f_(7/2),Ols和Cls光电子峰随CO_2气体暴露剂量的变化,分析表面各元素化学状态的变化和表面化学反应过程。实验表明,CO_2气体首先在清洁金属铀表面解离吸附形成碳粒子、氧粒子和碳氧粒子等。吸附解离的产物导致金属铀表面形成UO_2,UC和自由碳粒子并可能生成碳酸铀。讨论了CO_2气体与清洁金属铀表面的相互作用机理,并与以前研究的O_2和CO气体与清洁金属铀表面反应的现象与机理进行了比较。     

金属铀在氢氧化钠溶液中阳极氧化膜的XPS特性研究

采用X射线光电子能谱法（XPS）研究了金属铀在0．8mol/L NaOH溶液中阳极氧化膜的组成。结果表明，在本实验条件下，金属铀表面的阳极氧化膜主要由UO3和少量UO2 x组成；在超真空条件下，氧化膜中的部分 UO3逐渐还原成UO2 x。     

Analysis of fuel element matrix graphite corrosion in HTR-PM for normal operating conditions

The corrosion of spherical fuel element by oxidizing gases will degrade their thermal and mechanical properties in pebble-bed reactors. Oxidizing impurities in primary helium coolant may have significant influence on the gasification of graphite during the long service time even though their concentrations remain relatively low. This paper deals with the corrosion of matrix graphite by steam and oxygen in Chinese high temperature gas-cooled reactor pebble-bed module (HTR-PM). The influence of steam contents was first analyzed, and then the effect of oxygen contents was also taken into account. The results show that the corrosion by steam was weak and it would not threaten the normal service of spherical fuel elements for expected steam contamination levels. On the contrary, the corrosion would be more severe while the oxygen content was as high as currently expected. Finally, the upper limits of steam and oxygen in primary helium coolant were recommended to be 1.0 and 0.05 cm³ m⁻³.     

高温堆非纯氦气中预氧化对3种高温合金的腐蚀行为影响研究

高温气冷堆（简称高温堆）中,由于一回路冷却剂氦气中含有微量（ppm级）不纯杂质,其在高温环境中会对高温堆合金材料造成腐蚀,影响设备的性能。Inconel 617、Hastelloy X、Incoloy 800H是3种高温堆中间换热器及蒸汽发生器设备候选材料。研究表明,镍铬合金在高温下表面生成的富铬氧化层是防止合金在高温下发生严重腐蚀的重要因素。本文对3种合金在高温含杂质氦气中的腐蚀行为进行研究,探究预氧化对3种合金腐蚀行为的影响。并通过称重、扫描电镜、X射线能谱、电子探针显微分析仪以及碳硫分析仪对腐蚀结果进行分析。结果表明,3种合金均出现了不同的氧化和渗碳现象,预氧化对Hastelloy X合金抗腐蚀能力的提升不明显,对Inconel 617合金的抗氧化和渗碳能力有一定提升,对Incoloy 800H合金的抗渗碳腐蚀能力有一定提升。     

氚纯化装置的研制及性能验证研究

铀是一种传统的贮氚材料,在铀粉瓶中贮存的氚会不断衰变产生氦气,导致使用时氚的纯度下降,影响标记化合物产率。本研究设计了氚纯化装置,对装置进行安装调试,并对该装置中的铀床进行活化,利用该装置测定铀吸收氘单质气体的p-t曲线及在400~550 ℃范围的解吸氘气体的p-t曲线。应用调试好的系统对长期存放贮氚铀粉瓶中的氚进行纯化。结果表明,设计的氚纯化装置系统密封性好,经氦质谱检漏测定值为7.8×10^-13 Pa•m³/s;利用该装置测定氘的吸附饱和曲线,氘完全解吸时铀对氘的吸附量为240 mL/g。验证实验回收了久置铀粉瓶中的氚为1.44×10¹³ Bq,利用氦气体积推算出久置铀粉瓶中含氚质量百分率为53.1%。实验结果证实了系统纯化氚的可行性,可为氚标记化合物制备提供可靠的氚源。     

H、He离子辐照对国产ZIRLO合金氧化膜的影响

针对国产ZIRLO合金开展了H、He离子辐照对其腐蚀性能影响的研究。对国产ZIRLO合金样品分别进行高温（300 ℃）H、He离子辐照试验,辐照峰值剂量为1 dpa,之后进行模拟一回路腐蚀试验。通过腐蚀增重方法得到腐蚀动力学曲线。利用慢正电子湮没多普勒展宽谱对未辐照样品和辐照样品进行微观结构表征,用透射电子显微镜对腐蚀125 d的样品进行微观结构表征。结果表明,H、He离子辐照并未改变ZIRLO合金的腐蚀机理。He离子辐照产生的空位团可促进腐蚀过程中裂纹形核,增加了氧扩散通道,减少氧扩散激活能,导致腐蚀初期有明显的加速效应。H离子辐照对腐蚀的加速现象不如He离子辐照明显,原因是H离子辐照产生H-空位复合缺陷对氧扩散激活能减少作用较小。     

Uranium nitride fuels in superheated steam

Uranium mononitride (UN) pellets of different densities were subjected to a superheated steam/argon mixture at atmospheric pressure to evaluate their resistance to hydrolysis. Complete degradation of pure UN pellets was obtained within 1 h in 0.50 bar steam at 500 °C. The identified reaction products were uranium dioxide, ammonia, and hydrogen gas, with no detectable amounts of nitrogen oxides formed. However, the reaction could not be carried to completion, and the presence of uranium sesquinitride and higher uranium oxides or uranium oxynitrides in the solid residue is indicated. Evolution of elemental nitrogen was seen in connection with very high reaction rates. The porosity of the pellets was identified as the most important factor determining reaction rates at 400–425 °C, and it is suggested that in dense pellets, cracking due to internal volume increase initiates a transition from slow surface corrosion to pellet disintegration. The implications for the use of nitride fuels in light water reactors (LWR) are discussed, with some observations concerning hydrolysis as a method for ¹⁵N recovery from isotopically enriched spent nitride fuel.     

铀及其合金的水氧腐蚀机理分析

铀及其合金是重要的核材料,其水氧腐蚀研究受到广泛关注。本文系统总结了铀及其合金在真空和大气环境下的氧化反应过程、腐蚀速率和产物,并对不同研究者提出的反应机理进行讨论分析。其中铀-氧反应过程为氧气在表面的吸附、解离,O2-在晶格中进行扩散,O2-在金属和氧化物界面发生反应,其中扩散是反应速率的控制步骤。铀-水体系反应机理存在争议:进行扩散反应的离子是O2-还是OH-还没有一致的认识。铀-氧-水体系的反应是氧气和水气共同作用的结果,反应速率介于前两种体系之间。     

Design and experiment of hot gas duct for the HTR-10

A horizontal coaxial double-tube hot gas duct is a key component connecting the reactor pressure vessel and the steam generator pressure vessel for the 10 MW High Temperature Gas-cooled Reactor—Test Module. Hot helium gas from the core outlet flows into the steam generator through the liner tube, while helium gas after being cooled returns to the core through a passage formed between the inner tube and the duct pressure vessel. Thermal insulation material is packed into the space between the liner tube and the inner tube to resist heat transfer from the hot helium to the cold helium. The thermal compensation structure is designed in order to avoid large thermal stress because of different thermal expansions of the duct parts under various conditions. According to the design principal of the hot gas duct, the detailed structure design and strength evaluation for it has been done. A full-scale duct test section was then made according to the design parameters, and its thermal performance experiment was carried out in a helium test loop. With helium gas at pressure of about 3.0 MPa and a temperature over 900 °C, the continuous operation time for the duct test section lasted 98 h. At a helium gas temperature over 700 °C, the cumulative operation time for the duct test section reached 350 h. The duct test section also experienced 20 pressure cycles in the pressure range of 0.1–3.4 MPa, 18 temperature cycles in the temperature range of 100–950 °C. Thermal test results show an effective thermal conductivity of the hot gas duct thermal insulation is 0.47 W m⁻¹ °C⁻¹ under normal operation condition. In addition, a hot gas duct depressurization test was carried out; the test result showed that the pressure variation occurred on the liner tube was not more than 0.2 MPa for an assumed maximum gas release rate.     

CCl_(4)和HCl气体氯化铀氧化物北大核心CSCD

分别以CCl_(4)和HCl气体作为氯化试剂,进行了铀氧化物(主要为U_(3)O_(8))的氯化机理和各影响因素研究。以CCl_(4)为氯化试剂对U_(3)O_(8)粉末进行氯化,通过热重分析研究了氯化反应过程的机理及动力学行为,氯化产物主要为UCl_(4)。同时研究了CCl_(4)对不同种类和形态铀氧化物的氯化,UO_(2)芯块由于结构致密很难进行氯化,UO_(2)粉末和UO_(3)粉末很容易被CCl_(4)氯化,产物分别为UCl_(4)和UCl_(6)。以HCl气体为氯化试剂对LiCl-KCl熔盐中的U_(3)O_(8)粉末进行氯化,研究了反应温度、氯化时间、HCl气体流速、U_(3)O_(8)粉末投料量以及铀氧化物种类和形态的影响。结果表明,提高反应温度、延长反应时间、提高HCl气体流速,有利于氯化率的提高。推荐HCl气体氯化U_(3)O_(8)粉末的工艺参数为:氯化反应温度为500℃、HCl气体流速为0.6 L/min。     

Characterization of high flux magnetized helium plasma in SCU-PSI linear device

A high-flux linear plasma device in Sichuan University plasma-surface interaction(SCU-PSI)based on a cascaded arc source has been established to simulate the interactions between helium and hydrogen plasma with the plasma-facing components in fusion reactors.In this paper,the helium plasma has been characterized by a double-pin Langmuir probe.The results show that the stable helium plasma beam with a diameter of 26 mm was constrained very well at a magnetic field strength of 0.3 T.The core density and ion flux of helium plasma have a strong dependence on the applied current,magnetic field strength and gas flow rate.It could reach an electron density of1.2?×?10~(19)m~(-3)and helium ion flux of 3.2?×?10~(22)m~(-2)s~(-1),with a gas flow rate of 4 standard liter per minute,magnetic field strength of 0.2 T and input power of 11 k W.With the addition of-80 Vapplied to the target to increase the helium ion energy and the exposure time of 2 h,the flat top temperature reached about 530°C.The different sizes of nanostructured fuzz on irradiated tungsten and molybdenum samples surfaces under the bombardment of helium ions were observed by scanning electron microscopy.These results measured in the SCU-PSI linear device provide a reference for International Thermonuclear Experimental Reactor related PSI research.