Online monitoring system for metallic components in underground laboratory

With the increasing application of nuclear energy in power industry, China has accumulated a large amount of high-level radioactive nuclear waste, which are characterized by high toxicity, high radioactivity, and long half-life. Improper disposal will cause great harm to human life and property. China has decided to establish an underground laboratory for geological disposal of high-level radioactive waste (HLW) in Beishan, Gansu Province, to study the scientific issues related to geological disposal of HLW. In this paper, an online monitoring system including two kinds of integrated inductance probe for the corrosion monitoring of metallic materials used in atmospheric or bentonite environment in Beishan underground laboratory was developed, and the reliability and accuracy of the system were studied. The results show that the system can satisfy the requirement of online monitoring of the corrosion rate of metallic materials, ambient temperature, resistivity, and humidity of bentonite in the underground laboratory for geological disposal of HLW in different environments.     

Further results on the in situ anaerobic corrosion of carbon steel and copper in compacted bentonite exposed to natural Opalinus Clay porewater containing native microbial populations

Since 2012, a long-term in situ corrosion experiment (IC-A) is being conducted in the Mont Terri Underground Research Laboratory in Switzerland to investigate the corrosion behaviour of candidate canister materials in conditions representative of the Swiss concept for the disposal of high-level waste and spent nuclear fuel. To date, carbon steel and various types of copper coatings have been retrieved after different exposure periods of up to 3 years, and characterised to establish the composition of the corrosion product, the morphology of the corroded surface, the nature of the interaction between the metal and the surrounding bentonite, and the microbial populations in the bentonite and surrounding porewater. For carbon steel specimens, a complex corrosion product was identified, consisting predominantly of magnetite. Much less alteration on either the metal or the bentonite was observed in the case of copper samples. Low average anaerobic corrosion rates were measured for carbon steel and a very modest amount of alteration was identified on copper. The density and the initial form of the bentonite had a small influence on the rate of corrosion, across all materials. This paper summarises the results of the experimental programme obtained to date and discusses the relationship observed between exposure time and the evolution of the metal–bentonite interface for both carbon steel and copper.     

The anaerobic corrosion of candidate disposal canister materials in compacted bentonite exposed to natural granitic porewater containing native microbial populations

The materials corrosion test (MaCoTe) is a long-term, multinational in situ corrosion experiment setup at the Grimsel Test Site, Switzerland. The experiment has been operating since 2014 with a focus on the corrosion behaviour of container materials for the disposal of high-level waste and spent nuclear fuel under conditions representing a granitic deep geological repository. The experiment consists of eight modules containing metal coupons and bentonite. Two of the modules, each with a different bentonite density, have been retrieved after 394 days of exposure and have been analysed using a range of techniques aimed at studying the corrosion behaviour of the metals and the mineralogical evolution of the bentonite. Weight loss measurements show that carbon steel had a relatively low average corrosion rate (~2 µm year⁻¹). Much lower average corrosion rates were measured for the various types of copper (0.13–0.32 µm year⁻¹). No detectable corrosion was measured on stainless steel coupons. To date, no significant differences were observed in the corrosion behaviour and rate of the test metals in bentonite with different dry densities.     

Corrosion resistance of a cast steel overpack for high-level radioactive waste disposal in Japan

The corrosion rate and stress corrosion cracking (SCC) susceptibility of a cast steel are studied for its application to metal containers (namely overpacks) for geological disposal of high-level radioactive waste. Specimens for corrosion tests are cut from a prototype overpack manufactured by full-scale casting. Casting defects are widely distributed in the prototype overpack; however, the flat-bottom hole equivalent diameters for all defects detected by an ultrasonic test are 3.6 mm or less, which is relatively small. Forged steels and rolled steels are also tested for comparison of their corrosion properties with the cast steel. The corrosion rates are obtained by immersion tests in bentonite saturated with synthetic seawater under anaerobic conditions at 80°C for up to 1 year. The corrosion rate for the cast steel calculated by the weight loss during the experiments is close to that for the forged steels and rolled steels. The SCC susceptibility is examined using slow strain rate tests in a 1.5-mol L⁻¹ carbonate–bicarbonate solution, in which the occurrence of high-pH SCC is often reported for carbon steels. The SCC susceptibility increased with the increase in the carbon content of the products; however, there are no clear differences between casting and forging.     

Electrochemical behavior of carbon steel with bentonite/sand in saline environment

Current designs for the geological disposal of high-level radioactive waste in Japan use carbon steel overpack containers surrounded by a mixed bentonite/sand buffer material, which will be located in a purpose-built repository deep underground. Though there are many suitable sites for a repository in Japan, the coastal areas are preferable from a logistical point of view. It is, therefore, important to evaluate the long-term performance of the carbon steel overpack and the mixed bentonite/sand buffer material in the saline groundwaters of coastal areas. In the current study, the passivation behavior and initial corrosion rates of carbon steel with and without mixed bentonite/sand were tested as a function of the pH and salt concentration in representative saline groundwaters. The main findings indicate that the passivation of carbon steel encapsulated in a buffer material will be unlikely in a saline environment, even at high pH (12), and that the corrosion rate of carbon steel is more strongly affected by the presence of the buffer material than by the salt concentration.     

HCO3-和SO42-对Cu点蚀行为的影响

在不同浓度配比的HCO₃^-和SO₄^2-混合溶液中,利用循环极化电化学测试方法和SEM,对Cu工作电极的循环极化行为和点蚀表面形貌进行了系统的研究.结果表明,在高电位范围的循环极化实验中,Cu的点蚀行为可分为活性溶解型点蚀和钝化膜破裂型点蚀;随SO₄^2-浓度的升高Cu点蚀的敏感性增大.由于HCO₃^-与SO₄^2-的协同作用,随HCO₂^-浓度升高点蚀敏感性呈先增大后减小的规律.在钝化膜破裂型点蚀中,SO₄^2-提高Cu点蚀的诱发能力;HCO₃^-降低Cu点蚀的诱发能力.2种离子对点蚀自修复能力的影响无明显规律.     

硼酸缓冲溶液中pH值和Cl~-浓度对Cu腐蚀行为的影响

在硼酸缓冲溶液中,采用动电位极化、电化学阻抗谱(EIS)和半导体电容分析方法分别研究了Cu电极的极化行为及其表面人工Cu_2O钝化膜的化学稳定性.结果表明,低pH值、高Cl~-浓度均造成Cu_2O钝化膜的破坏和溶解.高Cl~-浓度时,Cu_2O钝化膜的半导体性质由p型转变为n型,使Cl~-更容易进入钝化膜与Cu~+络合,并破坏钝化膜从而加速腐蚀.高pH值、低Cl~-浓度有利于Cu_2O钝化膜稳定.     

Wear and corrosion properties of laser cladded Cu47Ti34Zr11Ni8/SiC amorphous composite coatings on AZ91D magnesium alloy

To improve the wear and corrosion properties of AZ91D magnesium alloys, Cu-based amorphous composite coatings were fabricated on AZ91D magnesium alloy by laser cladding using mixed powders of Cu47Ti34Zr11Ni8 and SiC. The wear and corrosion behaviours of the coatings were investigated. The wear resistance of the coatings was evaluated under dry sliding wear condition at room temperature. The corrosion resistance of the coatings was tested in 3.5% （mass fraction） NaCl solution. The coatings exhibit excellent wear resistance due to the recombined action of amorphous phase and different intermetallic compounds. The main wear mechanisms of the coatings and the AZ91D sample are different. The former is abrasive wear and the latter is adhesive wear. The coatings compared with AZ91D magnesium alloy also exhibit good corrosion resistance because of the presence of the amorphous phase in the coatings.     

Effect of substrate on the 3 body abrasion wear of HVOF WC-17 wt.% Co coatings

WC-17 wt.% Co coatings were deposited using high velocity oxy-fuel (HVOF) spraying onto four different substrate materials, namely aluminium, brass, 304 stainless steel and super-invar. These substrates have different coefficients of thermal expansion which have been shown to influence the final coating microstructural properties. The abrasive wear properties of the coatings were characterised using an ASTM-G65 three body abrasive wear machine with silica sand as the abrasive. The highest mass loss was recorded for the coating on the aluminium substrate whilst the coated 304 stainless steel showed the lowest mass loss. The coatings on brass and super invar experienced similar mass losses. SEM studies of the worn surfaces showed preferential removal of the Co binder phase as well as cracking and rounding of the carbide grains. The differences in wear behaviour may be attributed to the presence of residual stresses where the highest compressive residual stress led to the highest wear rate. The coatings deposited onto brass showed compressive stresses whilst those deposited onto super-invar had tensile stresses, yet these two coatings had similar wear rates. Thus further study is required to provide conclusive evidence of the role of residual stresses on the abrasion resistance of these coatings.     

Further studies on the anaerobic corrosion of carbon steel in alkaline media in support of the Belgian supercontainer concept

In the Belgian supercontainer concept, a carbon steel overpack surrounds high-level radioactive waste and spent fuel containers and is encased in a cementitious buffer material. Research has been carried out to characterise the anaerobic corrosion of carbon steel in an anoxic artificial alkaline porewater that simulates the cementitious buffer material and also in solid cement matrices, in the presence of chloride and the sulphur species expected in the groundwater. The current study focuses on recent results. Specifically, it provides an update on the long-term corrosion rates obtained from gas generation measurements (including new data from higher-sensitivity autoclaves) and weight loss measurements and provides results of postmortem analysis of dismantled cells. The behaviour of the system is discussed, focusing on the effects of the solution chemistry, precorrosion treatments and γ radiation on corrosion rates, the electrochemical response of the steel when irradiated, and the morphology of the corrosion product. The corrosion rate was lower in cement than in an aqueous system. Radiation affected the corrosion potential and the morphology of the corrosion product.     

Potential influence of microorganisms on the corrosion of carbon steel in the French high- and intermediate-level long-lived radioactive waste disposal context

In the context of the high-level radioactive waste disposal CIGEO, the corrosion rate due to microbially influenced corrosion (MIC) has to be evaluated. In France, it is envisaged to dispose of high- and intermediate-level long-lived radioactive waste at a depth of 500 m in a deep geological disposal, drilled in the Callovo-Oxfordian claystone (Cox) formation. To do so, a carbon steel casing will be inserted inside disposal cells, which are horizontal tunnels drilled in the Cox. A specific cement grout will be injected between the carbon steel casing and the claystone. A study was conducted to evaluate the possibility of MIC on carbon steel in the foreseeable high radioactive waste disposal. The corrosiveness of various environments was investigated at 50°C and 80°C with or without microorganisms enriched from samples of Andra's underground research laboratory. The monitoring of corrosion during the experiments was ensured using gravimetric method and real-time corrosion monitoring using sensors based on the measurements of the electrical resistance. The corrosion data were completed with microbiological analyses including cultural and molecular characterizations.     

Influence of Deteriorated Bentonite Sediments on the Corrosion Behavior of NiCu Low Alloy Steel

The corrosion evolution of steel disposal container largely depends on the evolution of surrounding bentonite environment in the long-term geological disposal of high-level radioactive wastes. This study focused on the influence of the deteriorated bentonite sediments on the corrosion behavior of NiCu low alloy steel in the top supernatant and bottom slurry formed by Gaomiaozi bentonite and 0.05 M NaHCO₃ + 0.1 M NaCl + 0.1 M Na₂SO₄ solution. In the top supernatant, the cathodic process of the steel corrosion was transformed from the reduction in oxygen to the reduction in ferric corrosion products with time as same as that in the blank solution. While in the bottom bentonite slurry, the cathodic process always maintained as the hydrogen evolution reaction due to the coverage of more bentonite sediments. Meanwhile, the corrosion rate of NiCu steel was obviously decreased. In addition, the localized corrosion tendency of the steel could also be reduced by the large amount of deteriorated bentonite sediments.     

AH32钢表面等离子喷涂制备疏水涂层及其耐腐蚀性能研究

目的提高AH32海洋用钢表面的疏水性及耐蚀性,并给出最佳性能的喷涂涂层成分。方法采用大气等离子喷涂技术,在AH32钢表面制备了三种不同成分的涂层。利用微量进样器结合半球法测量了涂层的接触角,并利用Qwen-Wendt公式对涂层的表面能进行了计算,利用扫描电子显微镜观察涂层的表面形貌,利用表面粗糙度仪测量涂层的表面粗糙度,利用冲刷实验及电化学工作站测量了不同涂层的耐蚀性能,并讨论了不同涂层的疏水机制及相应的腐蚀机理。结果等离子喷涂涂层显著改善了AH32钢的疏水性能。相比而言,等离子喷涂Co基涂层及等离子喷涂Ni基涂层与水的静态接触角达到了130°以上,均具有较好的疏水效果。三种涂层均明显改善了AH32钢的耐海水冲刷腐蚀能力,其中AH32钢基体腐蚀30d后的失重为1.68×10^-2 g/cm²,等离子喷涂Ni基涂层的腐蚀失重最小,约为4.2×10^-3 g/cm²。极化曲线测试结果也表明,三种涂层的自腐蚀电位较基体提高了300 mV左右,并且腐蚀电流密度较基体降低了1个数量级以上,另外Co基涂层的腐蚀电流...     

超音速火焰喷涂涂层的摩擦磨损性能研究

采用划痕分析和干砂粒/橡胶轮磨损测试,主要研究了超音速火焰喷涂(High-Velocity-Air-Fuel,简称HVAF )WC涂层与Al-Ni-Cu合金的摩擦磨损性能,并且与电镀硬铬的性能进行了对比.结果表明,HVAF WC涂层和Al-Ni-Cu合金都发生微量磨损,而电镀铬层中发生明显的增重,同时导致Al-Ni-Cu合金大量磨损.在与Al-Ni-Cu合金对磨中,HVAF WC涂层的磨损机理为磨粒磨损,而电镀硬铬为粘着磨损.滚动接触疲劳磨损对涂层均有作用.     

Study of accelerated corrosion test method for 16MnR steel waste containers in backfill materials

ABSTRACT

To research the long-term corrosion of 16MnR steel radioactive waste container in backfill materials that are lightweight aggregate concrete (LWAC) and Keerjian bentonite, accelerated corrosion test in the backfill environment was studied. The corrosive products during accelerated tests were compared to the ones during simulated tests through morphology observation, component analysis by XRD and grey correlation quantitative evaluation. An approach of the accelerated corrosion test combining enhancing medium with dry-wet alternation was designed. In either LWAC and bentonite enviroment, the corrosion rates of accelerated test and simulated test are quite different, but their corrosion products, corrosion laws and corrosion development trend are similar. For the zinc coating, the correlation coefficients of the accelerated test in LWAC and bentonite was 0.672 and 0.734, respectively. Moreover, the accelerated speedup of the designed accelerated corrosion test is greater than 337. Therefore, the designed accelerated corrosion test method has satisfactory correlation and acceleration effect.     

Corrosion domain analysis of copper corrosion in aqueous media

Abstract

The technology that is being developed in Sweden for the disposal of high level nuclear waste calls for storage of the waste in copper canisters, which are encapsulated in a bentonite buffer contained in drill holes in the floors of drifts (tunnels) in a granitic rock repository. A controversial issue has arisen during the development of this technology: that copper, when in contact with pure water under anoxic conditions corrodes and hence is not immune as previously believed. This issue is resolved in the present paper by deriving corrosion domain diagrams as a means of presenting the thermodynamics of the system in the clearest form possible, when assessing the immunity and activation of copper.     

基于In,Cu单镀液和纳米MoS2 复合镀液电刷镀层的抗粘着磨损性能研究

目的在Cr12MoV模具钢上电刷镀制备出多种具有自润滑性和减磨性能好的涂层,筛选出与奥氏体不锈钢对磨时抗粘着磨损性能优秀的镀层,改善模具的抗粘着磨损性能。方法采用电刷镀方法制备In,Cu单镀液镀层及Ni-W(D)-Mo S2(纳米)和Cu-MoS_2(纳米)复合电刷镀镀层,对4种镀层与1Cr18Ni9Ti奥氏体不锈钢进行对磨磨损实验,载荷为100 N,磨损时间为300 min,并分析磨损质量损失,同时采用扫描电镜观察分析各镀层的抗粘着磨损实验结果。结果 4种镀层都不同程度地提高了抗粘着磨损能力,但Cu单镀液镀层和Cu-MoS_2(纳米)复合镀层在磨损实验的前150 min磨损质量损失明显,磨损质量损失率分别达到0.105%和0.136%,而In和Ni-W(D)-Mo S2镀层都很小,分别为0.024 57%和0.031 74%,体现出更良好的抗粘着能力和耐磨性。结论在被加工工件的强度不高时,Cu镀层和Cu-MoS_2(纳米)复合镀层仍然具有一定的抗粘着磨损性能,而在被加工工件为具有较明显加工硬化现象的强度较高的奥氏体不锈钢时,In和Ni-W(D)-Mo S2镀层具有更好的抗粘着磨损性能,其中Ni-W(D)-Mo S2镀层表现出了最优秀的综合耐磨性。     

Overview of anaerobic corrosion of carbon steel radioactive waste packages in alkaline media in support of the Belgian supercontainer concept

The so-called supercontainer concept is currently being considered as the reference design for the final disposal of vitrified high-level radioactive waste and spent fuel in Belgium. It comprises a prefabricated Portland cement-based buffer that completely surrounds a carbon steel overpack. In this highly alkaline environment (pH ~13.6), and under normal conditions (i.e., without the ingress of aggressive species), the carbon steel overpack will be protected by a passive oxide film, which is expected to result in very low uniform corrosion rates. Considering the long timescales applicable to waste disposal, determining accurate and reliable estimates of the uniform corrosion rate under anoxic conditions forms a very important part of the safety and feasibility strategy. It is also crucial to demonstrate that no other form of corrosion apart from uniform corrosion takes place. This paper presents the progress of the research that has been made since the LTC2016 Workshop (Toronto, Canada) on uniform corrosion, pitting corrosion and stress corrosion cracking behaviour of P355 QL2 grade carbon steel exposed to an artificial concrete pore water solution.     

几种缓蚀剂对膨润土中16MnR钢的缓蚀作用

在放射性废物地质处置中,膨润土是首选的回填材料。膨润土膨胀、收缩过程中产生的应力会破坏废物容器的防腐蚀涂层;考虑到回填材料和地下水中含有的氯离子,可侵入到钢与膨润土界面,使钢去钝化而发生局部腐蚀。在结合工程实际的基础上,取现场地下水和柯尔碱膨润土对16MnR钢试片进行挂片腐蚀试验,分别添加六种常用的缓蚀剂,通过扫描电镜分析挂片表面腐蚀形貌,并用静态失重法计算腐蚀速率和缓蚀效率。试验结果显示,在0.5%的质量比添加条件下,缓蚀性能由高到低依次为亚硝酸钠、重铬酸钾、硅酸钠、钨酸钠、磷酸钠和钼酸钠,说明采用添加缓蚀剂改善16MnR钢废物容器腐蚀环境的方法是可行的。     

Evaluation of mass loss of weld-deposited hardfacing with cored wire Ti-FeCrC alloy

In this article, we have studied the mass loss of hardfacing applied by flux-cored arc welding. Heat input, shielding gas and number of layers of coating were changed to application of Fe–Cr–Ti–C self-shielded tubular wire. Overlapping beads were deposited on plates of carbon steel AISI 1020 to analyse the mass loss, hardness and microstructure. For the analysis of mass loss, beads were deposited forming overlapping layers of coatings. Hardness measurements were performed on the surface of the specimens of wear. A rubber wheel abrasion tester was used to access the mass loss of coatings. The coatings had retained austenite and martensite microstructure with carbides finely dispersed in the matrix. The main factors that contributed to the increase in mass loss were the cracks due to higher cooling rate of the samples deposited with low heat input, the dilution in the first layer of all samples also contributed to the increase in mass loss. The smallest mass losses were those deposited coatings with high heat input, the second and fourth layers, the samples AC2, AC4 and AS2. The volume fraction of titanium carbides contributed to the decrease in the mean free path between the particles of carbides and increased the wear resistance of the coatings.