Made available in DSpace on 2014-10-09T12:54:15Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:13Z (GMT). No. of bitstreams: 1 12438.pdf: 5594991 bytes, checksum: f79284c9b5ba64cbc05b0ee1eb78ef64 (MD5) / Tese (Doutoramento) / IPEN/T / The University of Tennessee

The fission product releases from spherical fuel elements used in modern high temperature gas cooled reactors are one of the first source terms used in describing the safety of planned nuclear plants during normal and accident conditions. The verification and validation of the model and code used to predict the gaseous fission product behaviour and release from spherical fuel elements for the PBMR were documented in this dissertation. The PBMR is the latest design in high temperature gas cooled reactor technology utilizing spherical fuel elements based on the LEU TRISO-coated particle design. Fission products can be divided into relatively short-lived noble gas and halogens, and relatively long-lived metallic fission and activation products. Each group is described by its own models and sets of transport parameters. The noble gases and halogen fission product releases from the fuel elements are direct indications of fuel performance and are modelled by the Booth equation. The fission product release legacy code NOBLEG for noble gases and halogens was developed previously to calculate this diffusion model for high temperature reactors. The model and code are verified and validated for use in PBMR design and analyses under normal operating conditions. The history of irradiation experiments conducted on coated fuel particles and spherical fuel elements was investigated, and the most suitable irradiation tests with their post irradiation investigations were identified for the purpose of validation of the model and code. The model used to determine gaseous fission product behaviour and release from spherical fuel elements is described in detail. The application of this model in the code is verified mathematically with the Booth model, and by inspection of the source code. The thermohydraulic model used by NOBLEG to calculate fuel temperatures is verified with code to code comparisons with the core neutronics code VSOP. The irradiation tests HFR-K5 and -K6 were selected to validate the gaseous fission product code NOBLEG. An investigation was done into the development of NOBLEG to calculate gaseous fission product release under oxidizing conditions caused by water ingress events. New relationships were derived from water vapour injection tests done during the irradiation experiment HFR-K6, that allows NOBLEG to estimate the increase in gaseous fission product release under oxidizing conditions. A new model was proposed to explain peculiarities observed during the water injection tests. / Prof. P.P. Coetzee

M.Ing. / Eskom's power stations receive their main supply of coal from mines next to the power stations. The coal supply contracts only specify maximum allowable variations of some coal quality parameters. The quality of the supplied coal can, however, vary greatly within a few hours. The boilers in the power plant are optimized for a certain quality of coal, while the supplied coal is burnt as it is received from the mine. The variations in the coal quality can, therefore, have a negative impact on both the life expectancy and maintenance costs of the power plant as well as the controllability of the boiler. The effects of short term variations in the coal qualities can be reduced by segregating the supplied coal into separate stockpiles according to coal quality parameters such as ash content and volatile matter, and then blending different portions from these stockpiles to a preferred coal quality before the coal goes to the boilers. A self organising feature map neural network was proposed in this research, to determine how to separate the supply coal, according to measured coal quality data. Furthermore, linear programming was proposed to determine the proportions to be taken from each stockpile in order to achieve a more consistent blended coal again. The segregating and blending systems are described in this thesis; and they were tested by means of a simulation based on measured coal quality data from a power station. It was shown that it is possible to successfully segregate coal from a single supply and then blend the different stockpiles to render coal with less short term variations in its quality parameters. The blending process uses stockpile size as its main driver to optimize the selection of the proportions, such that the most coal is taken from the largest stockpile, while the resultant coal quality remains within the specified constraints.

Scaling due to calcium carbonate precipitation is a major problem in cooling water circuits in many of Eskom power stations. Some earlier studies have suggested that the natural organic matter (NOM) present in the cooling water may reduce the amount of scaling by limiting the formation of calcium carbonate precipitation. It is therefore the interest of this study to investigate further the role of the NOM in calcium carbonate precipitation at Hendrina power station. The raw water and cooling water were analysed for the major metal ions, anions, alkalinity, conductivity and total organic matter to determine the precipitation potentials of calcite and aragonite using MINTEQA2 speciation program. The NOM was isolated from the raw and cooling water using ion exchange resins, XAD-8/XAD-4 resins and ultrafiltration membranes with molecular weight cut-offs of 100 kDa, 10 kDa and 1 kDa. The isolated fractions were then characterized by ultraviolet and visible absorbance methods and high performance size exclusion chromatography. The effect of the isolated fractions of the NOM from the cooling water on calcium carbonate precipitation was then investigated. The results indicated the presence calcium carbonate precipitation in the cooling water, but the raw water was undersaturated with calcium carbonate. The NOM isolated from the raw water indicated the predominance of the hydrophobic acid NOM (74.17 %) and to a lower extent the presence of hydrophilic acid NOM (34.49%). The NOM isolated from the cooling water also showed the predominance of the hydrophobic acid NOM (69.25 %) and to a lower extent the presence of the hydrophilic neutral acid NOM (20.13 %) and minimal presence of hydrophilic acid NOM (9.51 %). The results obtained from high pressure size exclusion chromatography analyses indicated that in both the raw water and cooling water the NOM was having a low molecular weight (<13.2030 kDa). The specific ultraviolet absorbance (SUVA) of the raw water was high (>4) which also suggested that it contained predominantly hydrophobic NOM and that of the cooling i water was in the range 2-4 suggesting that it contained a mixture of the hydrophobic and hydrophilic acid NOM. The hydrophobic acid, hydrophilic acid and hydrophilic neutral acid NOM fractions isolated from the cooling water reduced the amount of calcium carbonate precipitate formed in synthetic water sample. This effect was more pronounced with hydrophobic and hydrophilic acid NOM fractions than with the hydrophilic neutral acid NOM fraction. / Dr. M. Shumane

M.Tech. (Mechanical Engineering) / Eskom fossil fuel power stations operate under various conditions and the ageing fleet of fossil fuel power stations are under strain due to the rising demand in electricity. The quest for cheaper electricity in growing businesses and bringing foreign investment into South Africa is significant for economic growth. Therefore, minimizing operation costs and improving availability, reliability and thermal heat rate are key objectives for the operation of the business. Thermal heat rate calculation is a method used to assess the performance of fossil fuel power stations. It provides an indication of the thermal performance which reflects the condition and operation of the plant. This dissertation refers to the tools used to measure the condenser performance and to identify the reason for unhealthy condenser performance and an increase in thermal heat rate. Problem: Poor condenser performance causes significant losses in generation and thermal heat rate in fossil fuel plants. Loss in generation and thermal heat rate is caused by condenser backpressure. This has an adverse effect on turbine thermal heat rate and henceturbine efficiency. The performance of the condenser affects the turbine performance to a large extent. Decreased condenser performance will increase the turbine thermal heat rate, i.e. kJ/kWh, because of the increased steam consumption per kWh of energy generated and therefore lowering the overall turbine efficiency. This will result in poor thermal heat rate efficiency resulting in an increased coal burn rate, i.e. kg/kWh, and an increased fuel bill and carbon foot print for the fossil fuel power station. The aim of this dissertation is to determine the effects of condenser performance on thermal heat rate and to provide the engineering and operating personnel with a guide for monitoring condenser back pressure in order to improve turbine thermal heat rate and turbine efficiency. Method and Procedure: Chapter 4 describes the method and procedure used for the pre and post outage evaluation to cost-effectively determine the current condition of the condenser and to quantify the increase in thermal heat rate due to condenser degradation. The pre and post outage evaluation offered an opportunity to evaluate and quantify the effectiveness of the maintenance program and the value of the capital layout undertaken during the scheduled Unit outage. Findings: Chapter 5 discusses the findings of the pre and post outage data analysis of the condenser using the EtaPRO system as the tool. Re-tubing 50% of the condenser inner loop tubes and cleaning the other 50% of the outer loop tubes demonstrated a decrease in condenser backpressure and therefore an improvement in thermal heat rate. This will also result in an improvement in turbine cycle efficiency and reduce coal cost.

M.Sc. / The impact of air pollution by power stations on water quality, just like any other source of water pollution, is an issue of concern for all the water users since any degradation in water quality affects the water's suitability for use. The study area in which Majuba power station is located was chosen because it is in an area free of industrialisation, and is also part of the Vaal catchment. This catchment area is very important because of its water supply for Gauteng province and provides an ideal opportunity to monitor surface water pollution from atmospheric sources such as power stations. The purpose of this research is to investigate the chemical, physical and biological quality of surface water in the vicinity (within a 31 kilometre radius) of Majuba power station. The study will determine whether this power station is causing any salinity and acidity problems at the chosen sampling sites. Salinity and acidity are water quality problems associated with atmospheric pollution. The aim of the study is to determine whether proximity to Majuba power station has an effect on the surrounding surface water quality. The research was conducted by means of water quality sampling, analyses and assessment. Water quality samples were taken from six sites (Majuba 1 to Majuba 6) in the vicinity of Majuba power station over a period of three years (1997 to 1999). The approach was to take four samples in a year coinciding with the four seasons of the year. Due to logistical problems only two sampling trips were undertaken, during 1997. In 1998 and 1999 the full four sampling trips were undertaken however in some instances the river was dry or was flooded hence no samples could be taken at the affected sampling sites (although a trip to the sampling site was made). The biological analyses where done on site using the biomonitoring technique while chemical analyses were performed at the laboratory at Eskom. The biomonitoring assessment was done using the biomonitoring technique. The chemical results were assessed in terms of the suitability for use for the aquatic environment. This was done by using the water quality guidelines for the aquatic environment. The chemical results indicated that in terms of salinity and acidity the site closest to the power station, namely Majuba 1 had the worst water quality of the six sites. Majuba 1 also had the worst results in terms of biomonitoring. Majuba 2 indicated elevated salinity levels. The other four sites, namely Majuba 3 to 6, did not indicate either salinisation or acidification. However, the biomonitoring results at these sites indicated, with the exception of Majuba 4, some deterioration in water quality. Majuba 4 had the best water quality in terms of biomonitoring. Reasons for this could not be determined. At present it is still premature to say whether acidity in the water is a problem. This is a preliminary study and currently a more detailed multidisciplinary study that includes disciplines such as atmospheric deposition, groundwater chemistry, soil profiles and hydrology is being undertaken on the Upper Vaal catchment to comprehensively determine the impact of air pollution from power stations on the surface water quality. The proposal will be presented to the South African Water Research Commission. The ultimate aim of the multidisciplinary study is to inform decision makers in water quality management sector regarding the impact of air pollution on surface water quality, in order for them to put in place abatement technologies or strategies to mitigate surface water quality pollution.

M.Ing. / Along with the increased use of power-electronic devices, there has been an increase in the magnitudes of distorted currents. Much of the power-theory in use today was devised many decades ago, mostly for AC-systems with clean sinusoidal voltages and currents. Modem loads are more often no longer mostly linear. Against the background of a study in the basic mathematics underlying AC power theory, a few techniques concerned with per-frequency power were examined. In addition certain concerns surrounding the use of correlation indexes for the purposes of load identification were also examined.

M.Sc. / Worldwide, coal is one of the major sources of energy. In 1999 it was estimated that the global electricity generation from coal was about 36% of the total world electricity production (Knapp, 1999:11). With the combustion of coal for electricity generation however, negative environmental impacts occur. These are mainly caused by carbon dioxide, nitrous oxides, sulphur dioxide and particulate matter emissions. With an ever-growing global population, the need and demand for electricity is increasing. These needs and demands need to be addressed in an economically, socially and environmentally acceptable manner. In this study the author examines, analyses and compares the emissions from coalfired power stations in South Africa, Australia, Canada, Germany, India and the United States of America over a chosen period of time (1995-2001). The results of the study indicate, that, within the comparative group, South Africa is not the greatest producer of emissions from coal-fired power stations. It is the fourth biggest emitter of CO2. It has the highest SO2 emissions, because of the low-grade coal burned in the power stations that have been specifically designed to burn this type of coal. It is the second biggest emitter of NOx, and the third biggest emitter of particulates. Germany is the country that has shown the greatest progress in emissions reductions. This has been the result of restructuring and economic incentives. Overall, South Africa can be ranked third, on par with Australia.

The growing number of micro generation devices in the electrical network is leading many to consider that these devices can no longer be considered as fit and forget, but should instead be considered as having a demonstrable network impact which should be predicted and utilised. One of the techniques for considering the impacts of these devices is the Virtual Power Plant (VPP). The VPP is the aggregation of all the Distributed Generation (DG) connected into the network up to and including the connection voltage of the VPP, such that the cumulative power up the voltage levels can be seen in the single VPP unit, rather than across a broad spread of devices. One of the crucial tasks in characterising the VPP, developed in this work, is the ability to correctly predict and then aggregate the behaviour of several technology types which are weather driven, as a large proportion of DG is weather driven. Of this weather driven DG, some can only typically be dispatched with modification and the rest cannot be dispatched at all. The aggregation of the VPP as part of the electrical network is also developed, as the constraints of the network and the reliability of the network cannot be overlooked when considering the aggregation of the VPP. From a distribution network operator's (DNO) perspective, these characterisation models can be used to highlight problems in the network introduced by the addition of DG, but are also generally utilitarian in their role of predicting the power output (or negative load) found throughout the network due to DG. For a commercial agent interested in selling energy, these models allow for accurate predictions of energy to be determined for the trading period. A VPP agent would also be adversely affected by line failure in the network, leading to the development of an N-1 analysis based upon reliability rates of the network, which is used as the basis for a discussion on the impacts of single line failure and the mitigation available through feedback from the DNO.

Procedures for the selection, licensing and implementation of large scale energy projects must evolve with the escalating complexity of such projects and. the changing public value system. Government appeared unresponsive to rapidly changing conditions in the 1960s and 1970s. Consequently, approval of major hydroelectric development projects in British Columbia under the Water Act became increasingly more contentious. This led, in 1980, to the introduction of new procedures—the Energy Project Review Process (EPRP) — under the B.C. Utilities Commission Act. This study documents and evaluates the selection, licensing and implementation of the Revelstoke Hydroelectric Dam under the Water Act and assesses to what extent the current EPRP selection and licensing procedure overcame the shortcomings of the Revelstoke experience. The methodological approach used is that of a post-development analysis. The Revelstoke Project case study revealed that the Water Act only addressed project design, safety, and impacts, but not selection and justification. Project implementation proceeded under a conditional water licence. The two-part administrative framework, established under the licence and by B.C. Hydro, lacked integration and failed to provide effective management. A strong commitment to the preservation of environmental quality was lacking. The licensee's monitoring of construction practices in general and of compliance with environmental guidelines, a set of nonspecific commonly accepted construction activities, were inadequate. Governmental surveillance and enforcement were rendered unsatisfactory by staff shortages and a laissez faire attitude. The case study concluded with a post-development environmental analysis, which determined the effectiveness of the Environmental Impact Statement in predicting impacts to be only twenty-five percent. Evaluation of the EPRP and its application in the Site C Dam proposal demonstrated that it is a significant improvement over its predecessor. If applied efficiently and in its entirety, it would provide an adequate structure and procedural sequence for project selection and licensing. However, some of the inadequacies noted in the Revelstoke case study, such the lack of provisions for early public and government participation, an adequate data base, an administrative structure, and a post-development analysis, have not been or only partially corrected. To conclude, this thesis offers some recommendations to further improve this continually evolving process. / Arts, Faculty of / Geography, Department of / Graduate