核电厂乏燃料棒包壳表面氧化膜拉曼光谱分析

通过拉曼光谱法研究秦山核电厂一期反应堆内运行后的燃料棒Zr-4合金包壳外表面不同部位氧化膜的晶体结构。结果表明,在燃料棒底端,腐蚀程度相对较低,含有较高含量的四方相,表面也呈致密黑色,随着距底端的距离增加,腐蚀程度增加,外表面由黑白相间过渡到疏松白色,氧化膜中四方相氧化锆含量逐渐减少,逐渐转变为单斜相;在径向上,从氧化膜/金属界面到表面,四方相含量逐渐减少,单斜相氧化锆含量升高。与堆外试验结果类似,即四方相向单斜相氧化锆的转变决定锆合金包壳材料在堆内的抗腐蚀性能,单斜相含量越高,腐蚀速率越高,耐腐蚀性能越差。     

卧式铅铋堆芯氧化腐蚀特性研究

为开展卧式铅铋堆芯氧化腐蚀特性研究,本研究建立液态铅铋氧化腐蚀模型,并基于计算流体动力学方法,运用输运方程源项自定义方法实现耦合计算。研究表明,基准工况下堆芯燃料棒表面氧化层最厚位于出口位置处,中心位置燃料棒表面氧化层厚度显著高于靠近燃料组件盒燃料棒表面氧化层。10000 h后中心位置燃料棒表面仍保持双层氧化层结构,双层氧化层平均总厚度为1.32μm。本研究提出了铅铋堆芯氧化腐蚀特性数值模拟研究方法,能够用于铅铋堆芯氧化腐蚀的预测。     

秦山一期核电厂乏燃料棒包壳外表面氧化膜内应力研究

锆合金在压水堆中常用作包壳材料,而包壳的腐蚀限制了燃料的堆内使用寿命。为了增加核燃料的燃耗,有必要研究包壳的腐蚀过程。以秦山一期核电厂乏燃料棒为研究对象,对包壳外表面氧化膜的内应力和物相组成进行分析,对径向氧化膜显微形貌进行观察。结果表明,氧化膜中存在压应力,从燃料棒底端到顶端,应力逐渐减小,当降低到最低值时,应力逐渐稳定下来,最后在气腔处又突然增加;压应力对稳定四方相有着非常重要的作用,随着氧化层中裂纹与孔洞的发展,应力得到释放,氧化膜的物相逐渐转变为单斜相。     

F/M钢在超临界水环境中的腐蚀性能

本文研究了F/M钢在超临界水（SCW）环境中的腐蚀性能。实验结果表明,F/M钢在SCW中的抗腐蚀性能较差,温度、溶氧浓度以及材料中的Cr含量对其腐蚀性能有较大影响。对12Cr表面进行盐浴复合处理（QPQ）、电镀Cr和磁控溅射Cr处理,以研究其对F/M钢在SCW中抗腐蚀性能的影响。研究表明,经电镀Cr和磁控溅射Cr处理的12Cr试样在SCW中具有优良的抗腐蚀性能,尤其是经磁控溅射Cr处理的试样,1 000 h后其表面氧化膜依然完整致密,而经QPQ的试样腐蚀严重。     

应用QC活动提高钴棒环焊成品率

在QC(质量管理)小组活动中,通过现场调查和统计分析,找出了影响钴棒环焊缝成品率的主要因素,然后制订了相应的解决对策,将钴棒环焊缝成品率从87.1%提高到91.5%。     

基于涡流技术的燃料棒氧化膜测量信号有效性评估与统计

应用统计学中的中位数、四分位距概念并结合实践经验，研究了燃料棒氧化膜涡流测量信号在线及离线处理流程的优化方法，提出了使用标定信号检验结合氧化膜轴向变化趋势图进行在线的燃料棒氧化膜信号有效性评估，以减少事后复测带来的频繁吊运燃料组件的问题。同时，在对燃料棒氧化膜涡流信号进行离线统计时发现，相对平均数统计，中位数统计可以排除极端信号的干扰，燃料棒轴向长约150 mm区域段的氧化膜厚度数据的四分位距多数分布于0~3 μm。结果表明，使用中位数可以准确、直观地代表各个区域段的氧化膜厚度水平。      

燃料元件Zr—4端塞与钽管的焊接技术研究及其应用

介绍了压水堆燃料元件包壳Ｚｒ－４端塞与用于引入钨铼热电偶的钽管间的焊接技术及其焊缝的水压试验和腐蚀试验，结果表明焊缝表面成型良好，无冶金缺陷，承压９．０ＭＰａ未发现泄漏，焊缝在４５０℃熔融ＰｂＢｉ合金中经１００ｈ处理后有腐蚀迹象，但经预生氧化膜处理后能减缓ＰｂＢｉ的浸浊，最后提出了辐照罐设计和装配有时应采取的措施。     

利用激光处理改善不锈钢电子束焊缝性能研究

不锈钢为核工程常用结构材料,为改善其焊缝抗腐蚀性能,利用激光束对不锈钢焊缝进行快速熔凝处理的工艺试验和焊缝组织与性能的检验。实验结果表明:经激光处理后,焊缝及其热影响区表面的晶粒组织明显细化;成分偏析减少;焊缝区的塑性和抗腐蚀性质增加;热影响区的晶间腐蚀倾向得到改善。     

利用激光处理改善不锈钢电子束焊缝性能研究

不锈钢为核工程常用结构材料,为改善其焊缝抗腐蚀性能,利用激光束对不锈钢焊缝进行快速熔凝处理的工艺试验和焊缝组织与性能的检验。实验结果表明:经激光处理后,焊缝及其热影响区表面的晶粒组织明显细化;成分偏析减少;焊缝区的塑性和抗腐蚀性质增加;热影响区的晶间腐蚀倾向得到改善。     

燃料包壳腐蚀结垢机理及影响因素研究

燃料包壳结垢引起的腐蚀异常是导致燃料棒失效的重要原因之一。由于一回路水化学、反应堆运行模式、系统设备的更换、燃料设计和堆芯燃料管理等多种因素的综合作用，一回路系统释放的腐蚀产物（又称为污垢）会沉积在堆芯上部的燃料棒包壳表面，大量腐蚀产物的沉积会导致燃料棒包壳表面局部温度升高，引起包壳腐蚀加速，严重情况下会导致燃料包壳失效。本文对燃料包壳的腐蚀结垢机理进行研究，同时对其影响因素进行确定，为燃料包壳腐蚀结垢模型的建立奠定基础，对燃料棒综合性能分析中腐蚀模型的优化具有重要意义。     

热处理对含Nb锆合金焊接试样显微组织和耐腐蚀性能的影响

用真空电子束焊接方法将Zr-1.88Sn-0.35Fe-0.52Nb合金板与Zr-4板对接焊的样品,在400C、10.3MPa过热水蒸汽中腐蚀165d后,用光学显微镜从样品横截面上测量了焊接面和其背面不同部位的氧化膜厚度,并用透射电镜观察了不同部位锆合金的显微组织。结果表明:焊接样品经过500C退火处理,耐腐蚀性能明显提高,在相同的熔区和热影响区(含Nb侧)内,经过退火和未经退火的样品表面氧化膜的厚度相差10-20倍;焊接冷却时形成的bZr在退火时分解为aZr bNb是提高耐腐蚀性能的主要原因;焊接样品经过500C-1.5h退火处理后,熔区的耐腐蚀性能非常优良,在400C过热蒸汽中腐蚀165d后,氧化膜厚度未超过2mm,折算为腐蚀增重只有30mg·dm-2。根据电子探针的分析结果,熔区中的成分大约是Zr-1.2Sn-0.25Nb-0.25Fe-0.02Cr。     

Recovery of Heat-Generating Nuclides in Eluted Solutions

To study about microstructure and chemical composition of oxide films formed on surface of stainless steel is most important for understanding of stress corrosion cracking (SCC) and irradiation assisted stress corrosion cracking (IASCC). In this work, a new sample preparation method for microstructure observation of oxide films was developed. To prevent to break oxide films during fabrication, surface of specimens were protected with plating. Focused ion beam (FIB) processing was conducted to prepare thin foil samples of cross section of oxide films. After sample preparation, microstructure of cross section of oxide films was observed by transmission electron microscope (FE-TEM), and microscopic chemical composition was analyzed by energy dispersed X-ray spectrometer (EDS). From the results, effects of silicon (Si) doping for oxide film formation in two oxidation conditions are discussed.     

The effect of alloying modifications on hydrogen uptake of zirconium-alloy welding specimens during corrosion tests

The hydrogen uptake behavior during corrosion tests for electron beam welding specimens made out of Zircaloy-4 and zirconium alloys with different compositions was investigated. Results showed that the hydrogen uptake in the specimens after corrosion tests increased with increasing Cr content in the molten zone. This indicated that Cr element significantly affected the hydrogen uptake behavior. Fe and Cr have a low solubility in α-Zr and exist mainly in the form of Zr(Fe,Cr)₂ precipitates, which is extremely reactive with hydrogen in its metallic state. It is concluded that the presence of Zr(Fe,Cr)₂ second phase particles (SPPs) is responsible for the increase in the amount of hydrogen uptake in the molten zone of the welding samples after corrosion, as Zr(Fe,Cr)₂ SPPs embedded in α-Zr matrix and exposed at the metal/oxide interface could act as a preferred path for hydrogen uptake.     

Static and cyclic crack growth of low alloy steels in high-oxygen water simulating HDR test conditions

Steel samples of reactor pressure vessel and piping steels from the German HDR programme have been tested in high oxygen water at different temperatures simulating HDR test conditions. The specimens have been exposed to sequences of static and cyclic loading or to purely cyclic loading. During the tests, threshold stress intensity values for stress corrosion cracking and crack growth rates with various cyclic loading parameters were determined. Extensive fracture surface and oxide layer investigations were also performed. Water chemistry parameters such as dissolved oxygen content, pH and conductivity were continuously monitored during the tests. Finally, the measured laboratory water chemistry parameters were compared to those measured in the HDR plant during full scale testing of components and the relevance of the results for normally operating plants is discussed.     

Investigation of the corrosion behavior of 304L and 316L stainless steels at high-temperature borated and lithiated water

The effects of temperature and dissolved oxygen on the electrochemical behavior and the oxide film formation of grades 304L and 316L stainless steels at high-temperature borated and lithiated water were investigated by means of potentiodynamic polarization, scanning electron microscopy and X-ray photoelectron spectroscopy. The results revealed that increasing the solution temperature degrades the passivity of the oxide films formed on both grades of steel and shifts their corrosion potential toward more negative potentials. The oxide films formed on the steel samples immersed into the solution containing 20 ppb dissolved oxygen (DO) showed a duplex structure, in which the inner layer was mostly a composition of Cr oxides and the outer layer mainly was a Fe oxide and Ni–Fe spinel. Only a single layer of Cr-rich oxide was observed in the oxide films formed in the solutions with the DO concentrations higher than 20 ppb. Higher amount of Cr in the oxide films formed on the type 316L compared to 304L improves the passivity of the oxide film of this grade of steel and results in a wider passive region in its potentiodynamic polarization curves.     

The influence of proton irradiation on the corrosion of HT-9 during immersion in lead bismuth eutectic

The impedance properties of the oxide on the martensitic-ferritic steel HT-9 were characterized during proton irradiation at the LANSCE WNR facility. Prior to the irradiation experiment, samples were pre-oxidized in moist air resulting in an oxide scale that was on the order of 3 μm thick. Samples were then irradiated during immersion in 473 K lead-bismuth eutectic at a proton current of approximately 63 nA. To assess corrosion rate in real-time, a sinusoidal voltage perturbation was applied across the oxide surface as a function of frequency and the corresponding current response was measured. This method yielded values of oxide impedance which were used in conjunction with Wagner’s oxidation theory to calculate corrosion rate. In general, proton irradiation was associated with an increase in corrosion rate.     

含铝奥氏体耐热钢在超临界二氧化碳中的腐蚀行为

研究了20Cr-25Ni合金和一种新型结构材料含铝的奥氏体耐热钢(AFA钢)在600℃/20 MPa的超临界二氧化碳(S-CO₂)环境中的腐蚀行为,并对2种合金的氧化膜形貌、成分和结构进行分析。研究发现,20Cr-25Ni合金出现明显的腐蚀增重增长趋势,表现出“抛物线”上升规律;AFA钢腐蚀增重趋势缓慢,腐蚀1000 h后仅为2.11 mg/dm²。20Cr-25Ni合金表面出现粗大的氧化产物,随腐蚀时间延长,AFA钢的氧化膜始终保持致密、连续。通过氧化膜的截面形貌分析发现,20Cr-25Ni合金腐蚀后具有两层氧化膜结构,主要由Fe₃O₄和FeCr₂O4_氧化层以及少量尖晶石组成。而AFA钢中出现了3层氧化膜结构,中间和最内层分别为Cr₂O₃和Al₂O₃氧化膜,最外层分布了一层不连续的FeCr₂O₄尖晶石氧化物。由于形成了致密的...     

The Effect of Oxide Microstructure on Kinetic Transition in Out-of-pile Steam Corrosion Test for Zircaloy-2 and Nb-added Zircaloy-2

In order to study the mechanism of kinetic transition of corrosion rate for zirconium alloys, oxide films formed on Zircaloy-2 (Zry-2) and Nb-added Zircaloy-2 (0.5Nb/Zry-2) in steam at 673 K and 10.3 MPa were examined with TEM and SIMS.

Kinetic transition occurred at almost the same oxide thicknesses for both Zry-2 and 0.5Nb/Zry-2, but the corrosion rate after the transitions were quite different for the two alloys. Zircaloy-2 showed cyclical oxidation, while the weight gain of 0.5Nb/Zry-2 increased linearly.

The morphology and crystal structure were similar for the oxides of the two alloys and both the oxide films still mainly consisted of columnar grains even after the transition. Interface layers which mainly consisted of a-Zr crystallites were observed for both alloys and the oxygen content in the interface layers increased after the transition.

The solute concentrations of Fe, Cr and Ni became higher, accompanying the increase of oxygen concentrations at columnar grain boundaries in the oxide films after the transition for 0.5Nb/Zry-2. It was thought that the properties of grain boundaries of the 0.5Nb/Zry-2 oxide films changed after the transition, and the increase in oxygen diffusivity at grain boundaries caused the linear increase in weight gain.     

Effect of β phase, precipitate and Nb-concentration in matrix on corrosion and oxide characteristics of Zr-xNb alloys

The corrosion test and oxide characterization were performed on the specimens having different Nb-content in the range of 0-5 wt%. The specimens were heat-treated at 570 °C for 500 h to get the α+β_Nb phase and at 640 °C for 10 h to get the α+β_Zr phase after β-quenching. The corrosion tests were carried out at 360 °C. In the low Nb-contents of 0.1-0.2 wt% where Nb was soluble in the matrix without the formation of Nb-containing precipitates or β phase, the samples showed the excellent corrosion resistance and their corrosion resistance was not affected by heat-treatment. The corrosion resistance was improved by the stabilization of tetragonal ZrO₂ and columnar oxide structure when all added Nb was soluble in the matrix to equilibrium concentration. In the high Nb-contents of 1.0-5.0 wt%, the corrosion rate was very sensitive to the annealing condition. The transformation of oxide crystal structure from tetragonal ZrO₂ to monoclinic ZrO₂ and oxide microstructure from columnar to equiaxed structure was accelerated in the samples having β_Zr phase, while retarded in the sample having β_Nb phase. This means that the formation of β_Nb phase resulted in the reduction of Nb concentration in the α matrix, thus the corrosion resistance was enhanced with the formation of β_Nb phase. From the corrosion test and oxide characterization, it is suggested that the equilibrium concentration of Nb in the α matrix would be a more dominant factor to enhance the corrosion resistance than the Nb-containing precipitates, supersaturated Nb, and β phase (β_Nb or β_Zr).     

Analyses of oxide films grown on AISI 304L stainless steel and Incoloy 800HT exposed to supercritical water environment

Supercritical water (SCW) is being considered as a cooling medium for the next generation nuclear reactors because it provides high thermal efficiency and plant simplification. However, materials corrosion has been identified as a critical problem due to the oxidative nature of supercritical water. Thus, for safety using of these nuclear reactor systems a systematic study of candidate materials corrosion is needed. As in other high temperature environments, corrosion in SCW occurs by the growth of an oxide layer on the materials surface. The current work aims to evaluate oxidation behavior of AISI 304L SS and Incoloy 800HT in water at supercritical temperatures in the range 723-873 K under a pressure of 25 MPa for up to 1680 h. After exposure to deaerated supercritical water, the samples were investigated using gravimetry, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS). Oxide films grown on these materials have a layered structure with an outer layer consisting of a mixture of iron oxide/iron-nickel spinel oxides and an inner layer consisting of chromium oxide in the case of Incoloy 800HT and nickel-chromium spinel oxide in the case of AISI 304L SS. The mass gains for Incoloy 800HT at all temperatures were small, while comparatively with AISI 304L SS which exhibited higher oxidation rates. In the same time the results obtained by EIS indicate the best corrosion resistance of oxides grown on Incoloy 800HT surface.