8,437 research outputs found
Corrosion Dynamics of Carbon Steel in Used Fuel Container Environments
The current Canadian used nuclear fuel container (UFC) design uses a pressure‑grade carbon steel (CS) vessel with its outer surface coated with a thin layer of copper. One concern regarding the structural integrity of the UFC design is the potential internal corrosion of the CS vessel. Moisture trapped inside a UFC could condense within the gap between the hemispherical head and the cylindrical body of the vessel. The internal UFC environment will be exposed to a continuous flux of ionizing radiation arising from the decay of radionuclides trapped in the used UO2 fuel matrix.
This thesis research project investigates the effects of physical and chemical solution parameters on CS corrosion, with the aim of developing a corrosion dynamics model that can be used to assess the integrity of the current Canadian UFC design with confidence. The parameters studied in this thesis project were the ratio of solution volume to surface area, pH, dissolved O2, and the presence or absence of γ-radiation. Corrosion dynamics were followed using electrochemical techniques, both conventional and non‑standard techniques developed as part of this project. The electrochemical tests were augmented with post-test surface and solution analyses to study oxides formed on corroded surfaces and to determine the dissolved metal content in the solution phase.
The results of this study clearly demonstrated that CS corrosion involves many oxidation steps that lead to the formation and growth of different oxides as well as the dissolution of metal ions. The transfer of Fe atoms between metal, oxide and solution phases provides routes for developing strong systemic feedback that can induce autocatalytic reaction cycles, resulting in oscillatory behaviours that are observable under certain solution conditions. The dynamics of CS corrosion may not approach and reach only one steady state, but continue to evolve and reach different steady states, depending on solution parameters. A mechanism that can explain the CS corrosion dynamics over long time periods under a range of solution conditions has been proposed. The mathematical formulation of a model for the long-term corrosion of CS based on this mechanism has just begun. This study has shown that the corrosion dynamics in the early stages of corrosion can be easily modeled by applying classical electrochemical reaction rate equations coupled with mass transport flux equations. However, for CS in aerated solutions or other oxidizing environments, these classical equations must be formulated for the metal oxidation process rather than the reduction of solution species (oxidant) because the former process is rate determining
Measuring CEO Talent and Its Impact on Firm Performance: A Theoretical Integration and Empirical Analysis
This paper analyzes whether CEOs who are good contrarian investors, good forecasters, or good market timers can run their firms better. Besides using the timing measure which combines returns before and after the trade, we also use the past return measure to estimate the contrarian aspect of CEO trades and the future return measure to assess CEO’s ability to forecast stock returns. Our results suggest that CEOs’ managerial talent and valuation ability are primarily related to CEOs’ past return measure, while high post-trade returns indicate the expropriation motive for CEO trades. Overall, we obtain strong evidence to support the idea that CEOs who are good contrarian investors tend to run their firms better on average than other CEOs
Optimal Design and Ownership Structures of Innovative Retail Payment Systems
In response to the Fintech trend, an ongoing debate in the banking industry is how to design the new-generation interbank retail payment and settlement system. We propose a two-stage analytical model that takes into account the value–risk tradeoff in the new payment system design, as well as banks’ participation incentives and adoption timing decisions. We find that, as the system base value increases, banks tend to synchronize their investment and adoption decisions. When the system base value is low and banks are heterogeneous, bank association ownership maximizes social welfare. When both the system base value and bank heterogeneity are moderate, government mandate leads to the socially optimal solution. When the system base value is high and banks are relatively homogenous, government ownership is socially optimal. We offer important policy implications regarding the optimal system design and the government regulator’s role in shaping the banking industry in future financial innovation
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