3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item The effect of metal support interactions between a cobalt catalyst and carbon dots (Cdots) in cobalt fischer-tropsch catalysts(2018) Mokoloko, Lerato LydiaThe aim of this study was to introduce functionalized carbon dots (Cdots) as potential support and reducing agents for cobalt-based Fischer-Tropsch catalysts. Cdots with different physicochemical properties were synthesized from natural-based product such as ascorbic acid, sucrose and chitosan, using microwave-assisted reactions. Two types of Cdots, namely N-free Cdots (or Cdots) and N-doped Cdots, with particle sizes < 10 nm were produced. Both Cdots and N-doped Cdots have an amorphous structure, containing both sp2 and sp3 type carbon. The surface of Cdots contained mainly hydroxyl and carboxyl functional groups, while N-doped Cdots contained hydroxyl, carbonyl, and nitrogen-based (mainly pyridinic and pyrrolic) functional groups. Spinel Co3O4 nanoparticles with 10 nm crystallite sizes were synthesized from the “benzyl alcohol route”. Both the spinel Co3O4 nanoparticles and functionalized Cdots were used to prepare the inverse Co3O4/Cdots and Co3O4/N-doped Cdots catalysts. The in-situ XRD results showed that under H2 gas reduction conditions, the Co3O4/Cdots and Co3O4/N-doped Cdots catalysts increased the reduction temperature of Co3O4 to CoO and metallic Co, and Co (fcc) is the predominant form of metallic Co formed. However, when N-doped Cdots were used as both support and reducing agents, Co3O4 was reduced to both Co (fcc) and Co (hcp). The increase in reduction temperature of Co3O4 on Co3O4/Cdots and Co3O4/N-doped Cdots suggest the presence of strong metal to support interactions (SMSIs) between Co3O4 and functionalized Cdots. Further studies on the activity and selectivity of these prepared catalysts will be conducted under F-T reaction process.Item Dose reduction benefits of zinc injection into the primary cooling system of a pressurized water reactor(2018) Saaymans, Martin AnthonyKoeberg Nuclear Power Station has set itself the objective of achieving world top quartile performance in terms of dose to workers. Achieving this goal requires implementation of a number of dose reduction initiatives. One such initiative is the continuous injection of depleted zinc acetate into the primary cooling system of the plant as a means of cobalt reduction, the principal contributor to out-of-core radiation fields. The purpose of this research report is to investigate the measure of success in reducing the radiation dose that nuclear plants world-wide have achieved through zinc injection, and how Koeberg measures up to international results. The investigation method included an extensive literature study on international experiences and results of other cobalt reduction methods, the benefits of zinc injection, as well as the potential negative impact it may have on major plant components. The report also presents the results of Koeberg’s zinc monitoring programme while comparing it to international trends. A recommendation is made for a more coordinated monitoring programme at Koeberg in order to obtain maximum benefits in the long term. Notwithstanding, the research has led to the conclusion that Koeberg is achieving the desired results compared to industry performances for plants that are in the same phase of their respective zinc injection programmes.