Determining factors for anodic polarization curves of typical structural materials of boiling water reactors in high temperature – high purity water

In order to examine the anodic polarization characteristics of typical structural materials of boiling water reactors (BWRs), the anodic polarization curves of type 316L stainless steel (316L SS) and Alloy 182 were measured in deaerated high purity water at 553 K using the previously reported measurement method which was confirmed suitable for high temperature – high purity water. In order to specify which constituent element determines the dissolution characteristics of these materials, the anodic polarization curves of pure iron, pure nickel, and pure chromium were also surveyed. The anodic polarization curve of 316L SS was determined to have active, passive, and transpassive states which were the same as type 304 SS (304 SS) showed. But, Alloy 182 had different polarization characteristics especially near the corrosion potential as it had no active state. From comparison results of the polarization characteristics of these materials and their constituent elements, the corrosion characteristics of these materials were concluded to be mainly determined by the corrosion characteristics of chromium.     

Corrosion behavior of Hastelloy-N alloys in molten salt fluoride in Ar gas or in air

The effects of air on the corrosion of Hastelloy-N alloys in molten salt coolant containing fission product elements were investigated to determine the safety of structural materials in high-temperature reactors cooled with fluoride salt. Corrosion tests of Hastelloy-N in the molten fluoride salt FLiNaK in an alumina crucible and a graphite crucible under argon gas or air were performed at 773–923 K for 100 h. The depth of corrosive attack, as well as the extent of chromium and molybdenum depletion, increased with increasing temperature. The extent of Hastelloy-N corrosion in molten salt under air was significantly greater than under argon gas. The effect of adding the impurity cesium iodide to molten salt containing nuclear waste fuel on the corrosion behavior was negligible.     

熔盐冷冻壁应用中关键工艺影响因素研究

在熔盐堆燃料干法处理流程中,处理设备面临着严重的材质腐蚀问题。熔盐冷冻壁技术被视为保护相关设备耐受化学腐蚀的有效方法,而冷冻壁厚度的稳定控制是干法处理流程应用冷冻壁技术实现处理工艺目的的关键。基于自行研制的冷冻壁实验装置,模拟了干法处理中熔盐冷冻壁的应用工况,考察了导热油进口温度、熔盐初始温度、加热器功率、冷冻壁初始厚度对冷冻壁厚度变化的影响,得到了各个因素的影响规律,并总结了最佳的应用工艺条件。利用热流量的变化分析了冷冻壁厚度变化的原因:热流量越大,冷冻壁厚度减小量越大,达到平衡时,热流量越大,冷冻壁平衡厚度越小。通过实验数据拟合得到了线热流密度与冷冻壁平衡厚度的关系式,平均相对误差11.2%。     

Corrosion and microstructural aspects of dissimilar joints of titanium and type 304L stainless steel

To link titanium and zirconium metal based (Ti, Zr-2, Ti-5%Ta, Ti-5%Ta-1.8Nb) dissolver vessels containing highly radioactive and concentrated corrosive nitric acid solution to other nuclear fuel reprocessing plant components made of AISI type 304L stainless steel (SS), high integrity and corrosion resistant dissimilar joints between them are necessary. Fusion welding processes produce secondary precipitates which dissolve in nitric acid, and hence solid-state processes are proposed. In this work, various dissimilar joining processes available for producing titanium-304L SS joints with adequate strength, ductility and corrosion resistance for this critical application are highlighted. Developmental efforts made at IGCAR, Kalpakkam are outlined. The possible methods and the microstructural-metallurgical properties of the joints along with corrosion results obtained with three phase (liquid, vapour, condensate) corrosion testing are discussed. Based on the results, dissimilar joint produced by the explosive joining process was adopted for plant application.     

Cathodic polarization curves of the oxygen reduction reaction on various structural materials of boiling water reactors in high temperature–high purity water

Cathodic polarization curves of the O₂ reduction reaction were measured by using electrodes made from typical structural materials of boiling water reactors (BWRs) to evaluate the effects of kind of material on the electrochemical corrosion potential (ECP) calculation. To estimate ECPs at any region in the BWRs on the basis of the BWR environmental conditions, anodic and cathodic polarization curves should be obtained in advance under relevant conditions. The concentration of oxidants such as O₂ and H₂O₂ in coolant changes depending on the region in which they exist. As well, reduction reaction rates might differ depending on the kind of materials. In this work, the cathodic polarization curves of type 316L stainless steel (316L SS) and Alloy 182 were measured in high purity water at 553 K with different O₂ concentrations and compared with those of type 304 SS (304 SS). The results showed that the cathodic polarization curves differed depending on the kind of materials at the activation-controlled region. But, the difference in the ECP vs. O₂ concentration relationship was small when the ECPs were calculated by using both anodic and cathodic polarization curves measured on the objective material.     

Corrosion study of a highly durable electrolyzer based on cold crucible technique for pyrochemical reprocessing of spent nuclear oxide fuel

The application of the cold crucible technique to a pyrochemical electrolyzer used in the oxide-electrowinning method, which is a method for the pyrochemical reprocessing of spent nuclear oxide fuel, is proposed as a means for improving corrosion resistance. The electrolyzer suffers from a severe corrosion environment consisting of molten salt and corrosive gas. In this study, corrosion tests for several metals in molten 2CsCl–NaCl at 923 K with purging chlorine gas were conducted under controlled material temperature conditions. The results revealed that the corrosion rates of several materials were significantly decreased by the material cooling effect. In particular, Hastelloy C-22 showed excellent corrosion resistance with a corrosion rate of just under 0.01 mm/y in both molten salt and vapor phases by controlling the material surface at 473 K. Finally, an engineering-scale crucible composed of Hastelloy C-22 was manufactured to demonstrate the basic function of the cold crucible. The cold crucible induction melting system with the new concept Hastelloy crucible showed good compatibility with respect to its heating and cooling performances.     

Oxide layer stability in lead-bismuth at high temperature

Materials protection by ‘in situ’ oxidation has been studied in stagnant lead-bismuth, with different oxygen levels (H₂/H₂O ratios of 0.3 and 0.03), at temperatures from 535 °C to 600 °C and times from 100 to 3000 h. The materials tested were the martensitic steels F82Hmod, EM10 and T91 and the austenitic stainless steels, AISI 316L and AISI 304L. The results obtained point to the existence of an apparent threshold temperature above which corrosion occurs and the formation of a protective and stable oxide layer is not possible. This threshold temperature depends on material composition, oxygen concentration in the liquid lead-bismuth and time. The threshold temperature is higher for the austenitic steels, especially for the AISI 304L, and it increases with the oxygen concentration in the lead-bismuth. The oxide layer formed disappear with time and, after 3000 h all the materials, except AISI 304L, suffer corrosion, more severe for the martensitic steels and at the highest temperature tested.     

Corrosion of stainless steels in lead-bismuth eutectic up to 600 °C

An experimental program has been carried out to understand the differences in the corrosion behaviour between different stainless steels: the austenitic steels 304L and 316L, the martensitic steels F82Hmod, T91 and EM10, and the low alloy steel P22. The influence of oxygen level in Pb-Bi, temperature and exposure time is studied. At 600 °C, the martensitic steels and the P22 steel exhibit thick oxide scales that grow with time, following a linear law for the wet environment and a parabolic law for the dry one. The austenitic stainless steels show a better corrosion behaviour, especially AISI 304L. Under reducing conditions, the steels exhibit dissolution, more severe for the austenitic stainless steels. At 450 °C, all the materials show an acceptable behaviour provided a sufficient oxygen level in the Pb-Bi. At reducing conditions, the martensitic steels and the P22 steel have a good corrosion resistance, while the austenitic steels exhibit already dissolution at the longer exposures.     

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.     

Friction and wear of Inconel 690 and Inconel 600 for steam generator tube in room temperature water

In the steam generators of nuclear power plants, the flow of cooling water can cause the tubes to vibrate, resulting in fretting wear damage due to contacts between these tubes and their supports. The tubes are made of Inconel 690 and Inconel 600 and the supports are made of STS 304. In this paper, fretting wear tests in water were performed using the materials Inconel 690 and Inconel 600 in contact with STS 304. Fretting tests using a cross-cylinder type set up were conducted under various vibrating amplitudes and applied normal loads in order to measure friction forces and wear volumes. Also, conventional sliding tests using a pin-on-disk type set up were carried out to compare these test results.In the fretting tests, friction force was found to be strongly dependent on normal load and vibrating amplitude. Coefficients of friction decreased with an increase in the normal load and a decrease in the vibrating amplitude applied. Also, the wear of Inconel 600 and Inconel 690 was predicted using a work rate model. Depending on the normal load and vibrating amplitude applied, distinctively different wear mechanisms and often drastically different wear rates occurred. It was found that the fretting wear coefficients for Inconel 600 and Inconel 690 were 9.3×10⁻¹⁵ and 16.2×10⁻¹⁵ Pa⁻¹, respectively. This study shows that Inconel 690 can result in lesser friction forces and exhibits less wear resistance than Inconel 600 in room temperature water.     

Compatibility between several heat resistant alloys and sintered Li2O in static helium gas environment

The reaction of sintered Li₂O discs with several commercial heat resistant alloys has been investigated under the conditions of 3.3 × 10⁴Pa ($\text{1}\text{3}\text{atm}$) static He gas atmosphere in the temperature range of 500 and 750° C. Reaction products were identified by X-ray diffraction analysis to be two phases of Li₅FeO₄ and LiCrO₂. The former was dominant below 650° C and the latter was dominant above 650° C. The activation energies of the reaction were determined by the Arrhenius plots for weight changes and sub-scale thickness measurements. The reactivity of the four Fe-Ni-Cr alloys decreased according to the order of Incoloy 800, 316 SS, Hastelloy X-R and Inconel 600. Grain boundary penetration was observed above 500° C for Incoloy 800, 550° C for 316 SS and 600° C for Inconel 600. There was no grain boundary penetration in Hastelloy X-R.     

熔盐/辐照环境中细结构等静压石墨的结构和化学稳定性研究

熔盐堆以石墨作为反射体和慢化体,熔盐与石墨直接接触,石墨在熔盐中的腐蚀反应和辐照损伤是值得研究的问题。本文采用自主研发的细结构石墨,阻隔熔盐浸渗,采用30 MeV He+模拟中子辐照,研究不同温度及熔盐环境下石墨微观形貌、微结构和化学结构的变化。研究结果表明,高温环境下,由于高温的退火效应,石墨缺陷密度的增加及形貌的变化都远小于室温环境。辐照后的石墨与熔盐接触,其缺陷密度略微降低。这种微结构的改善与高温熔盐环境中的退火效应及熔盐固化引起内部微裂纹的闭合有关。辐照后的熔盐浸泡可在石墨C—C键结构中引入C—F键,且C—F键的形成与缺陷密度及缺陷类型密切相关。稳定的空位簇及间隙原子的迁移均会影响层间化合物的形成,从而产生限制C—F键形成的环境,进而降低由层间化合物的形成对石墨表面结构的破坏。     

316LN不锈钢在高温高压水环境下的腐蚀疲劳行为研究

在室温纯水、高温纯水及高温硼锂水环境下开展了316LN不锈钢在不同应变幅加载下的腐蚀实验研究，并获得了3种条件下的腐蚀疲劳寿命曲线。结果表明，316LN不锈钢在加载过程中出现了先硬化后软化现象，且随循环周次增加，应力峰值逐渐下降；高温纯水及高温硼锂水环境下材料的腐蚀疲劳性能下降，加速了材料的腐蚀疲劳失效；在高应变幅条件下高温的软化作用占主要影响，低应变幅条件下腐蚀作用占主要影响；试验后的样品断面上均可观察到疲劳辉纹、滑移变形带及二次裂纹，高温水腐蚀环境会加速裂纹扩展，加速疲劳失效。      

中国实验快堆粘钠设备动态去污技术模拟试验研究

采用硫酸和磷酸的混合酸作为去污剂,以530 ℃钠中浸泡3 700 h的304和316不锈钢为试样,进行了快堆设备去污模拟试验,并在去污试验后对试样进行去污深度、微观形貌以及力学性能等分析。结果表明：304和316不锈钢最大去污深度分别可达约10 μm和4 μm;材料去污深度随去污温度、时间、去污剂流速的增加而增大;相同条件下,304不锈钢的去污深度大于316不锈钢。去污后,材料均保持较好的延伸率,抗拉强度略有降低,不影响材料的整体力学性能。以12.5 g/L硫酸和30 g/L磷酸的混合酸一步法去污作为快堆粘钠设备的去污法具有操作简单、去污快、产生废液量少的特点,说明该混合酸是一种高效去污剂。     

The effects of low dose rate irradiation and thermal aging on reactor structural alloys

As part of the EBR-II reactor materials surveillance program, test samples of fifteen different alloys were placed into EBR-II in 1965. The surveillance (SURV) program was intended to determine property changes in reactor structural materials caused by irradiation and thermal aging. In this work, the effect of low dose rate (approximately 2 × 10⁻⁸ dpa/s) irradiation at 380–410°C and long term thermal aging at 371°C on the properties of 20% cold worked 304 stainless steel, 420 stainless steel, Inconel X750, 304/308 stainless weld material, and 17-4 PH steel are evaluated. Doses of up to 6.8 dpa and thermal aging to 2994 days did not significantly affect the density of these alloys. The strength of 304 SS, X750, 17-4 PH, and 304/308 weld material increased with irradiation. In contrast, the strength of 420 stainless steel decreased with irradiation. Irradiation decreased the impact energy in both Inconel X750 and 17-4 PH steel. Thermal aging decreased the impact energy in 17-4 PH steel and increased the impact energy in Inconel X750. Tensile property comparisons of 304 SURV samples with 304 samples irradiated in EBR-II at a higher dose rate show that the higher dose rate samples had greater increases in strength and greater losses in ductility.     

高温水中氯离子对316L不锈钢应力腐蚀裂纹扩展速率的影响

本文采用直流电压降(DCPD)方法,使用恒K(K=27.5 MPa·m1/2)加载方式,在核电厂高温高压水环境中研究了氯离子对316L不锈钢的应力腐蚀裂纹扩展速率的影响。实验结果表明:在高温除氧水中,氯离子会加快316L不锈钢的应力腐蚀裂纹扩展速率,且当水中存在溶解氧时,氯离子对应力腐蚀裂纹扩展速率的影响更明显。     

Corrosion experiments of steels in flowing Pb at 500 °C and in flowing LBE at 450 °C

In accelerator driven systems (ADS), as well as in the next Generation IV reactors, one of the concerned issues is the material compatibility and corrosion in liquid Pb, which is considered a candidate coolant. Liquid metal corrosion of the structural materials can proceed via different processes: species dissolution and penetration of liquid metal along grain boundaries and metal. The occurrence of these corrosion phenomenon depend on the experimental parameters, such as temperature, thermal gradients, solid and liquid metal compositions, velocity of the liquid metal and oxygen activity in Pb. One possible technique to prevent any corrosive attack by the liquid metals is the in situ passivation of the containment steels. This technique is achieved through an active control and monitoring of the dissolved oxygen concentration. This paper summarizes the data gathered from the CHEOPE III loop, where passivation of T91 and AISI 316L steels is tested in pure Pb at 500 °C were carried out, comparing them with preliminary corrosion data, in LBE, gathered from the LECOR loop.     

低浓去污预氧化过程中因科镍690合金我因科镍600合金的电化学 …

介绍了低浓去污预氧化过程中两种蒸汽发生器材料因科镍６９０合金及因科镍６００合金（下面简称６９０合金及６００合金）在不同邓氧化剂中脱膜效果（以铬的释放曲线表征）实验、腐蚀电位迁移测试和极化曲线测试。结果表明,６００合金在碱性高锰酸钾（ＡＰ）中的脱膜效果好于酸性高锰酸钾（ＮＰ）中,而６９０合金则在（ＮＰ）中的脱膜效果好于ＡＰ中。并且在ＮＰ中,随着硝酸浓度的增加,６００合金的腐蚀电位向正方向移动,６９０     

High-temperature tensile and creep data for Inconel 600, 304 stainless steel and SA106B carbon steel

We report results from high temperature tensile and creep tests performed on Inconel 600, 304 stainless steel and SA106B carbon steel, materials used to construct components which penetrate the lower heads of reactor vessels. Testing temperatures for the Inconel and stainless and carbon steels exceeded 1360 K, 1350 K and 1040 K, respectively. These data are applicable, but not limited, to severe accident analysis.     

Corrosion experiments and materials developed for the Japanese HLM systems

The static corrosion tests in lead-bismuth eutectic (LBE) were conducted from 450 °C to 600 °C to understand corrosion behavior and develop corrosion resistant materials for heavy liquid metal systems. While increase of Cr content in steels enhances corrosion resistance in LBE, the effect approaches a constant value above 12 wt% of Cr. Corrosion depth in LBE increases with increasing temperature and corrosion attack becomes severe above 550 °C even under the condition of high oxygen concentration. Nickel dissolution and Pb-Bi penetration occur in 316SS and JPCA above 550 °C under the condition of high oxygen concentration. When oxygen concentration decreases below the level of Fe oxide formation, corrosion attack on these steels also becomes violent due to dissolution of various elements and grain boundary corrosion. Whereas additions of 1.5 wt% Si to T91 and 2.5 wt% Si to 316SS improve corrosion resistance, the effect is insufficient taking fluctuation of oxygen concentration in LBE into consideration. Furthermore, addition of 1.5 wt% Si to T91 causes rise in DBTT. A new coating method using Al, Ti and Fe powders produces corrosion resistant coating layers on 316SS. The coating layers containing 6-8 wt% Al exhibit good corrosion resistance at 550 °C for 3000 h in LBE containing 10⁻⁶-10⁻⁴ wt% of oxygen.