Passivity degradation of nuclear materials in reduced sulfur environments: A review

Gao, Zhiming; Wang, Zeqing; Sun, Yinghao; Wu, Sibo; Ma, Chao; Zhu, Yu; Xia, Da-Hai

doi:10.1007/s12209-016-2811-y

Cited by 10 publications

(10 citation statements)

References 48 publications

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“…[1][2][3][4] SGs, which is used in pressurized water reactor (PWR) between the primary and secondary loops, are heat exchangers used to convert secondary-loop water into steam. 5 UNS N08800 is one of the most frequently used SG tubing materials, which has shown excellent performance in CANDU (CANada Deuterium Uranium) system without serious problems during long term service for almost 30 years. 6 Nevertheless, a few flaws have been found on some UNS N08800 tubesheet in two power plants designed by Siemens.…”

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confidence: 99%

“…8,9 The locations that corrosion degradation most possibly occurs are the crevices where are usually located between the tube-to-support plate and tube-to-tube sheet, or under deposits including thick freespan deposits and tubesheet sludge piles. 5,10 Some impurities including SO 4 2− and Cl − in the secondary loop water can concentrate within these crevices. 11,12 In order to avoid elevated corrosion potential of SG alloy and minimize oxygen content, hydrazine is intentionally added to the secondary loop of SGs, leading to a reduction of sulfate to HS − , H 2 15 which have been recognized to enhance active dissolution of metal, increase stress corrosion cracking and pitting susceptibility.…”

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confidence: 99%

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Factors Influencing Passivity Breakdown on UNS N08800 in Neutral Chloride and Thiosulfate Solutions

Wang

Shi

et al. 2017

J. Electrochem. Soc.

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In this work, the passivity degradation of UNS N08800 in solutions containing Cl − and S 2 O 3 2− is studied by using polarization curve, electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). Experimental results reveal that the passivity breakdown heavily depends on anodic potentials, concentration ratios of Cl − to S 2 O 3 2− , and the composition of materials. A combined effect between Cl − and S 2 O 3 2− on pitting corrosion is observed at high anodic potentials at which the passive film is broken down; in this situation, S 2 O 3 2− ions can enter into the pits by electromigration, and they are reduced to S ads and S 2− , stabilizing the metastable pits and accelerate the pit growth rate. However, there is no such combined effect at low anodic potentials when the passive film is intact, on the contrary, S 2 O 3 2− is beneficial to passivity in chloride solutions. At low anodic potentials, the interaction of S 2 O 3 2− with an intact passive layer is weak, and the adsorption of S 2 O 3 2− would mitigate the detrimental effect of Cl − ions.

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Factors Influencing Passivity Breakdown on UNS N08800 in Neutral Chloride and Thiosulfate Solutions

Wang

Shi

et al. 2017

J. Electrochem. Soc.

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“…6 Sulfur has many oxidation states, such as ¹2 in sulfide (S 2¹ ), 0 in sulfur (element), +2 in thiosulfate (S 2 O 3 2¹ ), +2.5 in tetrathionate (S 4 O 6 2¹ ), +3 in sulphite (SO 3 2¹ ), +6 in sulphate (SO 4 2¹ ) and so on. 34,35 Under the reducing environments, the lower oxidation states, such as ¹2 and 0 are more stable. The results of deposits and spectra taken from an energy dispersive X-ray (EDX) system confirmed the existence of reduced sulfur on alloy 600.…”

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confidence: 99%

“…1,37 S 2 O 3 2¹ is proved to be detrimental to SG tubing material, which is also well summarized in several reviews. 16,34,41,42 However, how S 2 O 3 2¹ interacts with Alloy 800 and how S 2 O 3 2¹ initializes the corrosion are still not solidly confirmed in the publications. There is little amount of solid experimental results related to Alloy 800.…”

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confidence: 99%

Pitting Corrosion Mechanism of Alloy 800 in Simulated Crevice Chemistries Containing Thiosulfate

Gao

Xia

et al. 2016

Electrochemistry

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Interaction of thiosulfate with Alloy 800 was systematically investigated to obtain the kinetics in a neutral simulated steam generator crevice solution. Cyclic polarization showed that the pitting potential in a thiosulfate-chloride solution was much lower than in either a chloride solution or a sulphate-chloride solution, and thiosulfate selectively and distinguishably degraded the oxide film on Alloy 800. The donor density of oxide film formed in a thiosulfatechloride solution was slightly higher than in either a chloride-only solution or a sulphate-chloride solution. Even in the passivity range the material was degraded due to the slow interaction with S 2 O 3 2− with oxide, especially when the applied potential was close to the pitting potential. The UV-visible absorption spectra showed that thiosulfate formed a stable complex with Cu 2+ , and their product was soluble in aqueous solution, which is possible evidence to indicate that thiosulfate assists Cu 2+ in dissolving from an oxide film into solution. Also, due to the complexity of the reaction, thiosulfate decreased the oxidation potential of Cu 0 to Cu 2+ . Since the Cu, an impurity in Alloy 800, normally accumulates at the grain boundary, especially at the triple points, thiosulfate induced corrosion is in the form of pitting or intergranular attack.

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“…In recent years, scanning electrochemical microscopy (SECM) has been developed for a wide range of applications in corrosion science. 12,13 An advantage of SECM is its capability to probe charge transfer occurring nonuniformly at interfaces. [14][15][16][17] Zhu et al investigated the impact of tensile and compressive stress on reactivity of the Alloy 800 C-ring sample using SECM and found that both tension and compression increased the localized surface reactivity, indicating corrosion susceptibility of Alloy 800 under stress in thiosulfate-contained chemistries.…”

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Hydrogen-enhanced Surface Reactivity of X80 Pipeline Steel observed by Scanning Electrochemical Microscopy

Xia

Zhu

et al. 2016

Electrochemistry

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Effect of hydrogen on the surface reactivity of X80 pipeline steel was studied by scanning electrochemical microscopy (SECM), electrochemical impedance spectroscopy (EIS) and secondary ion mass spectroscopy (SIMS). Hydrogen can enhance the reactivity of passive film formed on X80 pipeline steel, reduce the corrosion resistance and thickness of this passive layer, which is due to an increase in hydroxide in the passive layer.

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Passivity degradation of nuclear materials in reduced sulfur environments: A review

Cited by 10 publications

References 48 publications

Factors Influencing Passivity Breakdown on UNS N08800 in Neutral Chloride and Thiosulfate Solutions

Factors Influencing Passivity Breakdown on UNS N08800 in Neutral Chloride and Thiosulfate Solutions

Pitting Corrosion Mechanism of Alloy 800 in Simulated Crevice Chemistries Containing Thiosulfate

Hydrogen-enhanced Surface Reactivity of X80 Pipeline Steel observed by Scanning Electrochemical Microscopy

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