Radiation Induced Corrosion of Stellite-6

This thesis presents a study on the aqueous corrosion of a cobalt-based alloy, Stellite-6. Since aqueous corrosion kinetics are strongly influenced by water chemistry conditions (pH, temperature, and redox agents), a systematic study of Stellite-6 corrosion was carried out. The aim was to develop an ability to predict corrosion behaviour and particularly metal dissolution rates for cobalt alloys under a range of conditions. The work focused on a study of the influence of ionizing radiation on corrosion. This is of particular interest in the nuclear industry where radiation fields are present. Ionizing radiation creates oxidizing radiolysis products and alters the redox potential of a corroding solution. A series of electrochemical measurements and corrosion tests along with post-test surface analyses were performed. In doing these tests we gathered information on the state of the oxide formed during corrosion and the sensitivity of the oxide growth to the corrosion conditions. This is a more sophisticated approach than that used in many corrosion experiments that only examine a few facets of oxide formation. The combination of electrochemical measurements and surface analyses provided a highly detailed picture of oxidation. We found that corrosion proceeds through the formation of different oxides at different corrosion potentials. At higher potentials the result is the formation of a Co(OH)2 oxide layer on top of a CoCr2O4 layer. The rate and extent of oxidation and the rate of metal dissolution were sensitive to all parameters studied and particularly the pH of the corroding solution. Oxide growth is promoted and metal dissolution is suppressed at pH ~ 10 where the solubility of CoII is the lowest. The production of water radiolysis products via gamma irradiation was seen to have a net oxidizing effect and stimulated oxide growth at high pH. At all temperatures studied (25 to 150 °C) irradiation did not result in significant oxide compositional changes. However the extent of metal dissolution was seen to be dependent on a combination of both pH and solution electrolyte concentration, as well as the presence of ionizing radiation

Knowledge management national policies for moving towards knowledge-based development: A comparison between micro and macro level

Knowledge management is a business model that embraces knowledge as an organizational asset to drive sustainable business advantage. Nowadays the leaders know that they are moving towards knowledge era very fast and they should align all activities in a way that knowledge management facilitates the competition in a better way.Developed countries also try to apply knowledge policies all over their governance to deploy knowledge management in a national level. Existing studies have derived their findings from single perspective, organizational level, or country level, or in a better way, micro or macro level and have not considered a mutual perspective to cover all requirements in a systematic way and compare the micro and macro level for knowledge management establishment.This paper is aimed to bridge this gap through a framework resulted from the analysis of the research data

Exploring the governing transport mechanisms of corrosive agents in a Canadian deep geological repository

All nuclear energy producing nations face a common challenge associated with the long-term solution for their used nuclear fuel. After decades of research, many nuclear safety agencies worldwide agree that deep geological repositories (DGRs) are appropriate long-term solutions to protect the biosphere. The Canadian DGR is planned in either stable crystalline or sedimentary host rock (depending on the final site location) to house the used nuclear fuel in copper-coated used fuel containers (UFCs) surrounded by highly compacted bentonite. The copper-coating and bentonite provide robust protection against many corrosion processes anticipated in the DGR. However, it is possible that bisulfide (HS−) produced near the host rock-bentonite interface may transport through the bentonite and corrode the UFCs during the DGR design life (i.e., one million years); although container performance assessments typically account for this process, while maintaining container integrity. Because the DGR design life far exceeds those of practical experimentation, there is a need for robust numerical models to forecast HS− transport. In this paper we present the development of a coupled 3D thermal-hydraulic-chemical model to explore the impact of key coupled physics on HS− transport in the proposed Canadian DGR. These simulations reveal that, although saturation delayed and heating accelerated HS− transport over the first 100s and 10,000s of years, respectively, these times of influence were small compared to the long DGR design life. Consequently, the influence from heating only increased total projected HS− corrosion by − corrosion. Therefore, those parameters need to be carefully resolved to reliably forecast the extent of HS− corrosion

Measuring Key Parameters Governing Anion Transport Through Mx-80 Bentonite

The Nuclear Waste Management Organization (NWMO) is responsible for the design and implementation of Canada’s deep geological repository (DGR), which will be constructed ~ 500 m below ground surface to safely contain and isolate used nuclear fuel. Used fuel containers (UFC), designed by NWMO as part of multi-barrier system for DGR, comprises of an inner steel core with an outer copper layer that serves as a corrosion barrier. Surrounding the UFC, a highly compacted MX-80 bentonite (HCB) is used to suppress the transport of corrosive agents to the UFC and to limit the movement of radionuclides out of the DGR, in the highly unlikely event of a UFC failure. Under anaerobic conditions, sulfate-reducing bacteria at the interface of the host rock and bentonite may produce bisulfide (HS−) that can transport to the UFC surface and corrode the copper barrier. Therefore, it is crucial to understand HS− transport mechanisms through bentonite to assess the long-term DGR performance. Due to bentonite’s low permeability, HS− transport will be diffusion-driven; therefore, the apparent diffusion coefficient and retardation are critical parameters for the DGR performance assessment. This study aims to quantify HS− diffusion through bentonite using diffusion experiments under a range of anticipated DGR conditions (e.g., temperature, ionic concentration). This paper outlines the underpinning theory, experimental methodology developed to conduct experiments, and preliminary results. Altogether, this work bolsters confidence in the experimental design and methodology that will be used to determine necessary key parameters to model reactive transport of HS− through the DGR’s bentonite barrier

A Review of the Effect of Irradiation on the Corrosion of Copper-Coated Used Fuel Containers

Radiation induced corrosion is one of the possible modes of materials degradation in the concept of long-term management of used nuclear fuel. Depending on the environmental conditions surrounding the used fuel container, a range of radiolysis products are expected to form that could impact the corrosion of the copper coating. For instance, γ-radiolysis of pure water produces molecular oxidants such as H2O2 and the radiolysis of humid air produces compounds such as NOx and HNO3. This review is confined to a discussion of the effect of γ-radiation on the corrosion of copper-coated containers. A simplified mixed-potential model is also presented to calculate the extent of copper corrosion by using the steady-state concentration of H2O2 generated during the first 300 years of emplacement, when the radiation field is significant

A Review of the Effect of Irradiation on the Corrosion of Copper-Coated Used Fuel Containers

Radiation induced corrosion is one of the possible modes of materials degradation in the concept of long-term management of used nuclear fuel. Depending on the environmental conditions surrounding the used fuel container, a range of radiolysis products are expected to form that could impact the corrosion of the copper coating. For instance, γ-radiolysis of pure water produces molecular oxidants such as H2O2 and the radiolysis of humid air produces compounds such as NOx and HNO3. This review is confined to a discussion of the effect of γ-radiation on the corrosion of copper-coated containers. A simplified mixed-potential model is also presented to calculate the extent of copper corrosion by using the steady-state concentration of H2O2 generated during the first 300 years of emplacement, when the radiation field is significant