Zack Qin

Sulfide Film Formation on Copper under Electrochemical and Natural Corrosion Conditions

Abstract The mechanism and kinetics of Cu corrosion in anoxic aqueous chloride solutions containing sulfide (10−3 mol/L) have been investigated electrochemically and under natural corrosion conditi...

Kinetics of Corrosion Film Growth on Copper in Neutral Chloride Solutions Containing Small Concentrations of Sulfide

The corrosion behavior of oxygen-free copper in an anoxic 0.1 M NaCl + 5 × 10 ―4 M Na 2 S solution was studied using electrochemical impedance spectroscopy, scanning electron microscopy equipped with a focused ion beam, X-ray photoelectron spectroscopy and micro X-ray diffraction. The corrosion film grew as a coherent, compact crystalline layer with a nonuniform thickness. The growth kinetics obeyed a parabolic law consistent with control by a diffusion process. Once a coherent layer was established, film growth kinetics appeared to be controlled by Cu + ion diffusion through the film. At shorter times before a coherent film was established, SH- diffusion in solution exhibited a considerable influence on the growth rate.

Localized Dissolution of Millscale-Covered Pipeline Steel Surfaces

Abstract Electrochemical impedance spectroscopy, corrosion potential measurements, and surface analysis by scanning electron microscopy/energy-dispersive x-ray spectroscopy (SEM/EDX) and Raman spectroscopy were used to investigate the localized dissolution of millscale-covered pipeline steel surfaces. The porous millscale originally present on the pipe surface exerts an influence on the corrosion of the pipeline and may contribute to the eventual onset of stress corrosion cracking (SCC). Three regions in the corrosion potential-time plot were observed after exposure to an aqueous environment, corresponding to the initial attempts at breakdown of the millscale, coupling of the dissolution of the underlying steel to reductive dissolution of the millscale, and active corrosion of the steel at the base of pores in the film supported by water reduction either on the metal or on the millscale surface. The corrosion rate increases as the dissolved carbon dioxide (CO2) concentration increases. Changes in the solu...

Key parameters determining structure and properties of sulphide films formed on copper corroding in anoxic sulphide solutions

Abstract The corrosion behaviour of copper was studied in anoxic solutions containing different concentrations of sulphide (10−5–10−3 mol L−1) and chloride (0·1–5 mol L−1) under stagnant and controlled convective conditions. The main determinants of the structure and properties of the copper sulphide (Cu2S) films formed are the rate of sulphide transport to the surface relative to the rate of its interfacial reaction with copper, and competition between sulphide and chloride for surface adsorption sites. When sulphide diffusion is rate limiting, the sulphide film formed is porous and non-protective, whereas when film growth is not limited by mass transport of sulphide, the sulphide film is compact and protective. The results indicate that, under Swedish repository conditions, the film formed on copper will be porous and non-protective and its growth diffusion controlled.

The Influence of Preoxidation on the Corrosion of Copper Nuclear Waste Canisters in Aqueous Anoxic Sulphide Solutions

Scandinavian/Canadian high-level nuclear waste repository conditions are expected to evolve from initially warm and oxic to eventually cool and anoxic. During the warm, oxic period corrosion products will accumulate on the container surface. These deposits could impede the reaction of Cu with aqueous sulphide, the only reaction that could lead to the significant accumulation of additional corrosion damage under the long-term anoxic conditions. The kinetics of the reaction of Cu with aqueous sulphide solutions have been studied using electrochemical and surface analytical techniques. Corrosion potential measurements were used to follow the evolution of the surface as oxides/hydroxides were converted to sulphides in the sulphide concentration range 10{sup -5} to 10{sup -3} mol/L. Changes in composition were followed by in-situ Raman spectroscopy. Of critical importance is whether or not a period of pre-oxidation of a Cu container surface can prevent subsequent reaction of the surface with remotely produced sulphide. (authors)

Monte Carlo Simulations of the Degradation of the Engineered Barriers System in the Yucca Mountain Repository Using the EBSPA Code

Based on a probabilistic model previously proposed, a Monte Carlo simulation code (EBSPA) has been developed to predict the lifetime of the engineered barriers system within the Yucca Mountain nuclear waste repository. The degradation modes considered in the EBSPA are general passive corrosion and hydrogen-induced cracking for the drip shield; and general passive corrosion, crevice corrosion and stress corrosion cracking for the waste package. Two scenarios have been simulated using the EBSPA code: (a) a conservative scenario for the conditions thought likely to prevail in the repository, and (b) an aggressive scenario in which the impact of the degradation processes is overstated. (authors)

Sulphide-transport control of the corrosion of copper canisters

ABSTRACT The long-term anaerobic corrosion rate of copper canisters in a KBS-3 repository is calculated on the basis of sulphide-transport control. The nature of the anodic and cathodic rate-determining steps, as well as the controlling process for the overall corrosion reaction of copper in sulphide environments, are considered. Evidence indicates that the assumption of sulphide-transport control is valid for the overwhelming majority of ground water flow rates and sulphide concentrations considered in the Swedish SR-Site safety assessment. There is no evidence that canister lifetimes calculated on the basis of sulphide-transport control are non-conservative. This paper is part of a supplement on the 6th International Workshop on Long-Term Prediction of Corrosion Damage in Nuclear Waste Systems.

Predicting Radionuclide Release Rates from Spent Nuclear Fuel inside a Failed Waste Disposal Container Using a Finite Element Model

Models for the corrosion of spent nuclear fuel (fission and actinide-doped uranium dioxide) provide the essential source term for the release of radionuclides from within a failed nuclear waste con...

Modelling development of acidification within corroding sites on spent fuel surfaces

Abstract A model has been developed to predict whether the development of acidity is feasible within actively corroding sites on spent nuclear fuel (UO2) surfaces inside a failed nuclear waste container. The model simulations demonstrate that the build-up of acidity is possible within flaws and pores in a corroded UO2 surface, providing the separation of anodes and cathodes occurs. The extent to which the pH can be depressed is determined by the dissolution rate of the fuel, the dimensions of the defect, the local redox conditions which determine the corrosion potential, and the fraction of the fuel surface that is reactive. Based on the anticipated redox conditions established radiolytically in a failed container it is shown that a suppression of the pH sufficient to accelerate dissolution (pH≤5) is very unlikely.

Long Term Corrosion Behaviour of Carbon Steel During Anaerobic to Aerobic Cycling Under Near-Neutral pH Saline Conditions

This paper investigates the long term corrosion behaviour of pretreated carbon steel under alternating anaerobic to aerobic cycles over 238 days. Changes in steel behaviour were observed electrochemically by monitoring the corrosion potential, and calculating changes to corrosion rate from linear polarization resistance. With increasing cycle number the corrosion process becomes localized at a small number of locations, consistent with the formation of tubercles. Periods of aerobic corrosion were associated with more positive potentials (between −500 mV to −350 mV) and high corrosion rates (70 to 120 μm yr−1 ); whereas anaerobic corrosion yielded more negative potentials (< −650 mV) and lower corrosion rates (40 to 50 μm yr−1 ). Upon termination of the experiment, corrosion product deposits were characterized by several techniques: scanning electrochemical microscopy to detect morphology; focused ion beam and cross sectioning to judge film thickness and film porosity; and Raman Spectroscopy to identify iron phases.Copyright