Appropriate high level radioactive waste container materials in China are still under investigation. The corrosion behaviours of four types of materials (carbon steel Q235, aluminium alloy 2024, copper and stainless steel SUS 304) in simulated groundwater at room temperature were investigated. The corrosion rate was measured through the weight loss method. The chemical composition of corrosion product films formed on the surface of materials was investigated by means of X-ray diffraction and energy dispersive X-ray spectroscopy. The results showed that there was no crevice and pitting corrosion for carbon steel after one year of immersion; the corrosion was dominated by general corrosion, the composition of the corrosion product film being mainly γ-FeOOH, as well as Fe3O4. Copper underwent slight crevice corrosion, but aluminium alloy 2024 suffered serious localised corrosion. No corrosion was observed on stainless steel SUS 304. The presence of oxygen promoted crevice corrosion of copper and aluminium alloy 2024.
δ-ferrite usually plays an important role in the mechanical properties of martensitic stainless steel. However, there are few studies on the effect of δ-ferrite on hydrogen embrittlement (HE) in martensitic steel. In this study, the H-trapping of δ-ferrite and the effect on the HE in martensitic stainless steel is investigated. The hydrogen distribution characteristics were observed by atomic force microscope scanning (AFM), and the related results show that the δ-ferrite, martensite and δ-ferrite/matrix (F/M) interface can act as hydrogen traps. The martensite and F/M interface has the higher hydrogen-trapping capability, hydrogen diffuses in δ-ferrite is faster than that of martensite. During deformation, Electron Back Scatter Diffraction (EBSD) observation shown that the exist of δ-ferrite can release the stress concentration caused by the poor deformation ability of martensitic grains, and further improve the resistance of HE. The results provide valuable insights into the behavior of δ-ferrite in the HE.
The investigation described here was conducted to clarify the corrosion behaviour of high level radioactive waste containers made of copper. The influences of oxygen, chloride ion and sulphate ion on copper crevice corrosion were studied in solutions simulating groundwater characteristic of northwest China. The results showed that oxygen, chloride ion and sulphate ion promote crevice corrosion. Chloride ion was found to play a significant role in the crevice corrosion mechanism in copper, but sulphate ion had no effect on the mechanism.
During the separation between satellite and launch vehicles, large steel springs are often used as compression separation spring sets in a catapult separation system. Replacing the steel springs with titanium alloy springs could reduce weight by about 50%. Although titanium alloy springs have been widely used in the aerospace field due to their excellent performance, there are few reports on the design of high-precision titanium alloy springs. The current spring design standards mainly focus on steel springs with helix angles between 5° and 9°, which are not applicable to titanium springs. Moreover, the change in spring rate with ambient temperature should also be considered. In this paper, β-C titanium alloy was used to design and prepare large compression separation springs, replacing steel springs in the catapult separation system. The design of titanium alloy springs took into account the big helix angle. The relationship between helix angle and the number of active coils was calculated. The parameters of titanium alloy springs were determined by the shear stress of the spring at working length. The effects of aging temperature and aging duration on the mechanical properties and modulus of β-C alloy were studied. By adjusting the aging process, the β-C alloy spring rate was controlled to meet the design requirements. The effect of ambient temperature on the mechanical properties and modulus of β-C titanium alloy were also investigated. It was found that as the ambient temperature increased, the rate of the β-C alloy spring gradually decreased.
Abstract 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.
Carbon steel is a candidate material for the disposal container of high-level nuclear waste in a deep geological repository in China, which will be subject to general corrosion and localised attack. In this work, the effects of Cl−, SO42– and CO32− concentrations on the general corrosion and crevice corrosion of carbon steel were studied by immersion tests and electrochemical measurements. The results show that Cl− promotes general corrosion, while SO42− and CO32− inhibit general corrosion. In a single ion solution, SO42− is the most obvious in promoting the crevice corrosion, which is different from the result of carbon steel in groundwater solution. Cl−, rather than SO42−, dominates the crevice corrosion process of carbon steel in groundwater solution.This paper is part of a supplement on the 6th International Workshop on Long-Term Prediction of Corrosion Damage in Nuclear Waste Systems
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