三代核电机组一回路钝化加氢工艺问题研究及改进应用

三代核电机组在热态功能试验（简称热试）期间需执行加氢钝化,以改善一回路表面钝化效果。国内某三代核电机组首次执行一回路加氢时速率较慢,导致一回路氢气测量值无法在预计时间内达到钝化开始时的限值。我们结合现场实际情况,分析了问题的相关环节,并在满足系统正常运行要求和工业安全要求的前提下,针对影响因素进行处理和优化,合理改进原有加氢方案,保证热试期间一回路的加氢速率,节约热试工期,对后续三代核电、“华龙一号”机组的建设有参考意义。     

核级不锈钢焊接接头钝化膜耐蚀性能和半导体特性研究

采用电化学阻抗谱(EIS)、场发射扫描电子显微镜(SEM)、Auger扫描能谱仪(AES)以及容抗测试技术(M-S曲线),研究了316LN/316L不锈钢焊接接头在模拟压水堆一回路高温高压水中形成的钝化膜的耐蚀性能和半导体特性。结果表明,焊缝区、热影响区和母材区形成的钝化膜的耐蚀性能不同,热影响区钝化膜开路电位及电化学阻抗等均低于其他区域,说明热影响区钝化膜的耐蚀性能最差,这主要与钝化膜的致密程度、厚度及Cr氧化物的含量有关。M-S曲线表明,母材区钝化膜平带电位为-0.7V,较其他区域(-0.4V)负移,表明有BO-3等阴离子在钝化膜表面吸附,加之具有较低的施主和受主浓度,可排斥侵蚀离子的腐蚀,使之较其他区域有更强的耐蚀性能。     

硝酸溶液中铝的电化学溶解行为

铝常用作核燃料的包壳材料以及辐照靶件的基体材料。研究其电化学溶解行为对于开发新型铝基体首端溶解工艺具有重要意义。研究了铝在硝酸中的阳极溶解电化学行为,并测定一系列条件下铝阳极的电化学阻抗谱、极化曲线和循环伏安曲线。结果表明:在稳态时,铝表面形成钝化膜,钝化膜的厚度随硝酸浓度的升高先下降后升高,在硝酸浓度为4mol/L时厚度较薄;体系的温度升高、硝酸铝浓度下降都使钝化膜的厚度减小;在有极化电流作用下,升高温度、增大酸度以及增大硝酸铝浓度,都易于使膜击穿,从而实现阳极溶解;铝在硝酸中的溶解速率仅与电流强度有关,电解速率可达0.4g/(A·h)。     

O钝化对铀铌合金电化学腐蚀行为的影响

采用电化学方法研究了铀铌合金经CO（0.3MPa)钝化前后的电化学耐蚀性能，并用X射线光电子能谱（XPS）分析了铀铌合金经CO钝化后表面层的组成。研究结果表明：铀铌合金经CO钝化后表面生成了致密的钝化膜，这层钝化膜增大了腐蚀过程的阳极阻力，提高了铀铌合金的电化学耐蚀性能。     

304奥氏体不锈钢在不同浓度硝酸中的电化学行为

采用动电位极化曲线测量、开路电位测量等技术,研究了304奥氏体不锈钢在不同浓度硝酸溶液中的电化学腐蚀行为,并对304奥氏体不锈钢在硝酸溶液中的电化学反应历程进行了探讨。结果表明：304奥氏体不锈钢在硝酸溶液中具备不锈钢典型的极化曲线特征,有多个钝化区和过钝化区;硝酸浓度升高促进不锈钢表面钝化膜的生成,使开路电位向正电位方向移动,降低了硝酸溶液对不锈钢的腐蚀倾向,同时,随着硝酸浓度的升高,不锈钢的点蚀电位升高,提高了不锈钢耐点蚀能力;在硝酸溶液中,不锈钢的腐蚀速率同时受到酸度和硝酸根浓度的影响,二者相互矛盾,导致硝酸浓度对腐蚀速率的影响呈不规律性。结果表明,在0.5 mol/L硝酸中,不锈钢的腐蚀速率最高。     

HEDP对硝酸去污体系中1Cr18Ni9Ti的腐蚀影响

采用失重腐蚀实验、电化学测试、金相及电子扫描探针观测,研究在硝酸清洗条件（浓度10%HNO3、温度50℃）添加HEDP对1Cr18Ni9Ti的腐蚀影响。结果表明：添加HEDP后1Cr18Ni9Ti在HNO3体系的耐点蚀性能进一步提高,且HNO3与HEDP的二次钝化现象有一定的协同作用,有利于1Cr18Ni9Ti在HNO3体系中钝化膜被破坏后的再修复。初步证明了添加HEDP到HNO3作为反应堆一回路管道拆除前非破坏性清洗去污试剂配方的可行性。     

秦山核电厂调试期间一回路的水质控制

为尽量减少秦山核电厂一回路系统设备的腐蚀,以及减少冷却剂循环污染和降低一回路系统的放射性,在冷态试验和热态功能试验阶段,堆装料、启动和功率运行试验阶段,都进行了一回路水质控制。本文介绍了一回路水质控制方法,并着重介绍了冷却剂的pH值、氯离子、溶解氧、溶解氢的控制以及硼与锂的协调。秦山核电厂的调试获得令人满意的成功,一回路水质控制也是卓有成效的。     

高温气冷堆用石墨材料的腐蚀实验与软件模拟

在高温气冷堆进水进空气事故下,空气和水蒸气会与堆内的石墨材料发生化学腐蚀反应,从而可能影响反应堆的安全。为研究高温气冷堆内石墨材料的氧化腐蚀特性,本文利用气相色谱法实验测量了IG-110石墨在不同温度和不同气体组分配比情况下的腐蚀速率及腐蚀产物,并利用THERMIX/REACT软件对整个石墨腐蚀过程进行了模拟。研究结果表明：反应温度对石墨腐蚀的影响最为显著,腐蚀速率随着温度的升高而增大,同时随着温度升高,CO与CO₂的含量比也逐渐增大。通过与实验结果对比分析,验证了THERMIX/REACT软件用于高温气冷堆安全分析的可靠性。     

金属铀在水气气氛中加速腐蚀的实验研究

用热重法研究了铀在50～90℃和32%～86%湿度范围的水气气氛中的加速腐蚀,得到了该实验条件下铀的水气腐蚀特性,并对反应的动力学进行了讨论。结果表明:在不同温度、湿度条件下,铀在水气气氛中的腐蚀动力学过程表现为较为明显的3阶段,动力学过程最后为线性反应阶段,该阶段有一稳定的氧化反应速率常数。RH=74.7%时线性反应的活化能约为42.899kJ·mol-1。温度对反应速率的影响明显,温度升高,反应速率加快。     

焊接残余应力对316LN不锈钢应力腐蚀裂纹扩展速率的影响

核电站不锈钢管道焊接过程中引入的残余应力对焊接接头的应力腐蚀开裂性能有较大影响。本文针对一AP1000主管道316LN不锈钢焊接模拟件进行残余应力分析和应力腐蚀裂纹扩展速率测量,得到了焊后原始状态和去应力热处理状态的焊接热影响区材料在高温高压水中的应力腐蚀裂纹扩展速率。实验结果表明,焊接残余应力明显提高了热影响区的应力腐蚀裂纹扩展速率,且在含氢的压水堆一回路正常水化学下焊接残余应力的影响更加显著。     

Investigation of passive films on nickel Alloy 690 in lead-containing environments

Passive films formed on Alloy UNS N06690 were investigated in simulated crevice chemistries. It was found the role of lead in corrosion processes is strongly dependent on the pH value of the testing solutions. At pH 1.5 the effect of lead is narrowly noticeable; while at pH 12.7, lead has a significant influence on the electrochemical performance of alloy UNS N06690. The lead alters the surface morphologies at both pH and account for higher hydroxide content in the surface film at pH 12.7. The lead incorporation hinders the formation of spinel oxides during the passivation in alkaline solution. Nanoindentation tests indicate a significant lead-induced degradation in the mechanical properties of passive films. The passivation degradation is attributed to detrimental effects of lead via interrupting the dehydration process and hindering the formation of protective layers on the alloy surface.     

低浓度硼对锆合金缓蚀作用研究

采用动电位极化和电化学阻抗谱法（EIS）研究了核电厂包壳材料锆合金在3种pH值相同的正常硼锂水质中的高温电化学腐蚀行为；采用高压釜腐蚀增重和微观分析等手段研究了锆合金在2种锂浓缩水质中的均匀腐蚀行为。高温电化学腐蚀试验表明:在3种pH值相同的正常硼锂水质中，随着硼浓度的增加， 锆合金的钝化电流密度减少而交流阻抗值增大，硼对减缓锆合金的腐蚀有利。均匀腐蚀试验表明:相对于无硼的锂浓缩水质而言，加硼显著降低了锆合金的腐蚀增重量，减少了氧化膜厚度，并使氧化膜更为致密，对提高锆合金的耐锂浓缩加速腐蚀有明显作用。      

一种显色表征不锈钢钝化膜质量的新方法

文章提出一种基于显色反应和颜色测量来表征不锈钢加工过程中钝化膜质量的新方法,比较了蓝点溶液和邻菲罗啉溶液对显色检测的影响,并建立了显色检测值与不锈钢电化学腐蚀特性的关系。结果表明,显色检测值越小,不锈钢钝化膜越致密;蓝点溶液对不同钢种的检测灵敏度高,但蓝点溶液破坏不锈钢表面质量且溶液稳定性差;邻菲罗啉溶液检测不同钝化状态钝化膜的灵敏度高,对不锈钢表面无明显影响、溶液稳定性好;邻菲罗啉溶液显色检测值a*＜3时不锈钢耐蚀性较好,当a*＞3时不锈钢耐蚀性相对较差。     

Corrosion of single layer thin film protective coatings on steel substrates for high level waste containers

Single-layer thin film coatings have been deposited on steel substrates and tested for their corrosion resistance. These coatings include TiN, ZrO₂, TiO₂, Al₂O₃, and MoS₂, and it is proposed that they will act as barriers to provide protection to the steel canisters that are part of the dry cask storage system for high level nuclear waste. Corrosion testing was completed using electrochemical potentiodynamic polarization techniques in aerated 1 M NaCl solution. Results show an exponential increase in corrosion rate with increasing temperature and an exponential decrease in the passive breakdown overpotential, which is directly related to the ability of a material to form and sustain a corrosion-inhibiting passive film in a given environment. Additionally, kinetic activation parameters have been experimentally determined for each material, leading to predictive equations for corrosion rates. The bare and coated samples corrode analogously, indicative of pores allowing the coating and substrate to corrode simultaneously. The samples were also placed in circulating salt brines of varying pH as a supplementary corrosion testing mechanism to explore their corrosivity over extended time. Negligible weight change was experienced by the bare and coated steel samples over a period of 5 months. Increasing the coating thickness and the number of layers may provide higher resistance to uniform and localized corrosion.     

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.     

热挤压690合金管材在高温水中的长期均匀腐蚀行为

采用长期浸泡和表面膜俄歇电子能谱（AES）与扫描电子显微镜（SEM）分析方法研究了热挤压690合金管材3段不同挤出顺序的管段（头部A、中部B和尾部C）在高温除氧水中的均匀腐蚀行为与机理。结果表明：热挤压690合金管材头部A、中部B和尾部C 3种试样在浸泡2 500 h后均匀腐蚀均达到稳定状态，其均匀腐蚀速率均低于5 mg/(月•dm²)；头部A与尾部C的腐蚀速率相当，而明显低于中部B的腐蚀速率；氧化膜呈双层结构特征，即外层富Fe和Ni、内层富Ni和Cr，A与C试样氧化膜中间层存在铬壁垒，而B试样无明显的铬壁垒。     

Correlation between composition of passive layer and corrosion behavior of high Si-containing austenitic stainless steels in nitric acid

Austenitic stainless steels with 18% Cr have a good corrosion behavior in pure nitric acid. However, when oxidizing power of the solution increases, this kind of stainless steels faces a severe intergranular corrosion. Adding a sufficiently high concentration of silicon to the steel avoids this type of corrosion: in oxidizing solutions, those stainless steels exhibit generalized corrosion but their dissolution rate is higher than the one of stainless steels without silicon. To find out the role of silicon on such effects, the corrosion behavior of two different stainless steels with equivalent chromium content but with different silicon content (304L steel and Uranus S1N) has been studied in concentrated nitric acid solutions. Correlations have been evidenced between the passive layer composition investigated by XPS analysis and the corrosion behavior characterized by electrochemical techniques. The presence of silicon in the steel changes neither the oxidation state of chromium or iron, nor the ratio between iron and chromium in the passive layer. Silicon is present in the passive layer in an important content (35 at.%) and thus decreases the chromium content of the passive layer (80 and 50 at.% respectively for 304L steel and Uranus S1N after nitric passivation). Uranus S1N exhibits a less protective passive layer and so its generalized corrosion rate is higher than the one of 304L steel. A selective deposition of platinoïds highlights differences of polarization distribution on the surface between the grain boundaries and grain faces for theses steels. For Uranus S1N, the similar electrochemical behavior of grain boundaries and faces might be connected with the homogeneous silicon distribution.