A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2015 / Spent nuclear fuel storage is gradually becoming a nightmare for nuclear reactors which were commissioned in the 1980s. This leaves the nuclear facility management with the dilemma of having to choose between pursuing the cask storage option to relieve the demand pressure on the spent fuel pool, or to opt for the more radical but unpopular option of shutting down the reactor compromising the energy supply, and South Africa is no exception. In a bid to minimise the risk of reactor shut down, the Nuclear Analysis Section (NAS) of Eskom launched the present study of investigating the design requirements of spent fuel casks suitable for the storage and transportation of spent fuel assemblies that have an initial enrichment of up to 5 wt% and much higher burnup of between 50 and 60 GWD/MTU. The aim of the present study is to investigate the suitability of the existing casks for use in 5 wt% enriched fuel, given that they are licensed for a maximum enrichment of 3.5 wt%. As a result of the huge number of casks required, there is potentially a risk of shortage of cask storage space and, therefore, it was prudent that the study also investigates the most optimum storage array that will maximise the storage space, while keeping the effective neutron multiplication factor (keff) below the internationally recommended value of 0.95 [IAEA, 2014]. As such, it is also necessary to identify parameters which have the greatest effect on the neutron multiplication factor. These include determining the effect of changes in moderator and fuel temperature on the neutron multiplication factor and also what the effect of an increase in the concentration in 10B of the boral plate will have on the neutron multiplication factor. / M T 2016

There is at present some uncertainty as to what the roles and requirements of the next generation of UAVs might be and the configurations that might be adopted. The incorporation of technological features on these designs is also a significant driving force in their configuration, efficiency, performance abilities and operational requirements. The objective of this project is thus to provide some insight into what the next generation of technologies might be and what their impact would be on the rest of the aircraft. This work involved the conceptual designs of two new relevant full-scale UAVs which were used to integrate a select number of these advanced technologies. The project was a CASE award which was linked to the Flaviir research programme for advanced UAV technologies. Thus, the technologies investigated during this study were selected with respect to the objectives of the Flaviir project. These were either relative to those already being developed as course of the Flaviir project or others from elsewhere. As course of this project, two technologies have been identified and evaluated which fit this criterion and show potential for use on future aircraft. Thus we have been able to make a contirubtion knowledge in two gaps in current aerospace technology. The first of these studies was to investigate the feasibility of using a low cost mechanical thrust vectoring system as used on the X-31, to replace conventional control surfaces. This is an alternative to the fluidic thrust vectoring devices being proposed by the Flaviir project for this task. The second study is to investigate the use of fuel reformer based fuel cell system to supply power to an all-electric power train which will be a means of primary propulsion. A number of different fuels were investigated for such a system with methanol showing the greatest promise and has been shown to have a number of distinct advantages over the traditional fuel for fuel cells (hydrogen). Each of these technologies was integrated onto the baseline conceptual design which was identified as that most suitable to each technology. A UCAV configuration was selected for the thrust vectoring system while a MALE configuration was selected for the fuel cell propulsion system. Each aircraft was a new design which was developed specifically for the needs of this project. Analysis of these baseline configurations with and without the technologies allowed an assessment to be made of the viability of these technologies. The benefits of the thrust vectoring system were evaluated at take-off, cruise and landing. It showed no benefit at take-off and landing which was due to its location on the very aft of the airframe. At cruise, its performance and efficiency was shown to be comparable to that of a conventional configuration utilizing elevons and expected to be comparable to the fluidic devices developed by the Flaviir project. This system does however offer a number of benefits over many other nozzle configurations of improved stealth due to significant exhaust nozzle shielding.The fuel reformer based fuel cell system was evaluated in both all-electric and hybrid configurations. In the ell-electric configuration, the conventional turboprop engine was completely replaced with an all-electric powertrain. This system was shown to have an inferior fuel consumption compared to a turboprop engine and thus the hybrid system was conceived. In this system, the fuel cell is only used at loiter with the turboprop engine being retained for all other flight phases. For the same quantity of fuel, a reduction in loiter time of 24% was experienced (compared to the baseline turboprop) but such a system does have benefits of reduced emissions and IR signature. With further refinement, it is possible that the performance and efficiency of such a system could be further improved. In this project, two potential technologies were identified and thoroughly analysed. We are therefore able to say that the project objectives have been met and the project has proven worthwhile to the advancement of aerospace technology. Although these systems did not provide the desired results at this stage, they have shown the potential for improvement with further development.

A steady-state simulation of a diesel-fuelled SOFC system was developed using a process simulation software package (VMGSim). The system was studied by conducting a sensitivity analysis of six independent variables (steam to carbon ratio, oxygen to carbon ratio, fuel utilization, air utilization, reformer pre-heater approach temperature and cathode temperature to the SOFC) and their effect on three response variables (net system efficiency, stack efficiency, system exhaust temperature). The steam to carbon ratio, fuel utilization and air utilization were the most influential independent variables and thus affected the greatest change in the performance metrics. Secondly, a multi-variable study was carried out on the most influential variables and constrained optima for the efficiencies (45% net system, 47% stack) and system exhaust temperature (78 degrees Celsius) were obtained. For the second part of this work, a steam reforming heat-exchange reactor was modeled using COMSOL. The reactor performance was assessed on the basis of selectivity and residence time for a given conversion. Both the kinetic models of Parmar et al. (2010) and Shi et al. (2009) for catalytic diesel steam reforming were applied and compared. Differences in performance were attributed to differences in the catalyst support and the reaction mechanisms used for deriving the reforming rate expressions. Finally, a proof of concept multi-scale modeling and design tool was developed by integrating the CFD model with the process simulation. Two-way communication between four different software components; COMSOL, VMGSim, Matlab and Microsoft Excel was achieved. / Thesis (Master, Chemical Engineering) -- Queen's University, 2012-04-18 01:12:27.072

There is at present some uncertainty as to what the roles and requirements of the next generation of UAVs might be and the configurations that might be adopted. The incorporation of technological features on these designs is also a significant driving force in their configuration, efficiency, performance abilities and operational requirements. The objective of this project is thus to provide some insight into what the next generation of technologies might be and what their impact would be on the rest of the aircraft. This work involved the conceptual designs of two new relevant full-scale UAVs which were used to integrate a select number of these advanced technologies. The project was a CASE award which was linked to the Flaviir research programme for advanced UAV technologies. Thus, the technologies investigated during this study were selected with respect to the objectives of the Flaviir project. These were either relative to those already being developed as course of the Flaviir project or others from elsewhere. As course of this project, two technologies have been identified and evaluated which fit this criterion and show potential for use on future aircraft. Thus we have been able to make a contirubtion knowledge in two gaps in current aerospace technology. The first of these studies was to investigate the feasibility of using a low cost mechanical thrust vectoring system as used on the X-31, to replace conventional control surfaces. This is an alternative to the fluidic thrust vectoring devices being proposed by the Flaviir project for this task. The second study is to investigate the use of fuel reformer based fuel cell system to supply power to an all-electric power train which will be a means of primary propulsion. A number of different fuels were investigated for such a system with methanol showing the greatest promise and has been shown to have a number of distinct advantages over the traditional fuel for fuel cells (hydrogen). Each of these technologies was integrated onto the baseline conceptual design which was identified as that most suitable to each technology. A UCAV configuration was selected for the thrust vectoring system while a MALE configuration was selected for the fuel cell propulsion system. Each aircraft was a new design which was developed specifically for the needs of this project. Analysis of these baseline configurations with and without the technologies allowed an assessment to be made of the viability of these technologies. The benefits of the thrust vectoring system were evaluated at take-off, cruise and landing. It showed no benefit at take-off and landing which was due to its location on the very aft of the airframe. At cruise, its performance and efficiency was shown to be comparable to that of a conventional configuration utilizing elevons and expected to be comparable to the fluidic devices developed by the Flaviir project. This system does however offer a number of benefits over many other nozzle configurations of improved stealth due to significant exhaust nozzle shielding.The fuel reformer based fuel cell system was evaluated in both all-electric and hybrid configurations. In the ell-electric configuration, the conventional turboprop engine was completely replaced with an all-electric powertrain. This system was shown to have an inferior fuel consumption compared to a turboprop engine and thus the hybrid system was conceived. In this system, the fuel cell is only used at loiter with the turboprop engine being retained for all other flight phases. For the same quantity of fuel, a reduction in loiter time of 24% was experienced (compared to the baseline turboprop) but such a system does have benefits of reduced emissions and IR signature. With further refinement, it is possible that the performance and efficiency of such a system could be further improved. In this project, two potential technologies were identified and thoroughly analysed. We are therefore able to say that the project objectives have been met and the project has proven worthwhile to the advancement of aerospace technology. Although these systems did not provide the desired results at this stage, they have shown the potential for improvement with further development.

A novel batch reactor concept is proposed for the catalytic production of hydrogen in distributed and portable applications. In the proposed CHAMP (CO2/H2 Active Membrane Piston) reactor, a batch of hydrocarbon or synthetic fuel is held in the reaction chamber where it reacts to produce hydrogen with simultaneous removal of the hydrogen by permeation through an integrated, selective membrane. These processes proceed to the desired level of completion at which point the reaction chamber is exhausted and a fresh batch of fuel mixture brought in. Unique to the CHAMP reactor is the ability to precisely control the residence time, as well as the ability to compress the reaction chamber dynamically, or mid-cycle, in order to increase the instantaneous hydrogen yield rate. An idealized reactor model demonstrates that the ideal limits of performance (in the absence of transport limitations) exceed those of comparable continuous flow designs. A comprehensive, coupled, transport-kinetics model is used to quantify the effects of mass transport limitations on reactor performance and search the design parameter space for optimal points. Two modes of operation are studied: fixed-volume mode wherein the piston is stationary and constant-pressure mode in which the rate of compression matches the permeation of hydrogen through the membrane. Finally, to validate these numerical models and confirm our understanding of the key operating principles, prototype reactors were built and experimentally characterized.

No description available.

Die vorliegende Arbeit beschäftigt sich mit der Entwicklung eines dieselbetriebenen autothermen Reformierungssystems (ATR-Einheit) zur Bereitstellung von wasserstoff- und kohlenmonoxidreichem Synthesegas für den maritimen Betrieb einer MCFC-Brennstoffzelle. Aufgrund der niedrigen Schadstoffemissionen sowie des hohen Wirkungsgrades hat dieses System das Potential eine mögliche Alternative zu den bisherigen Schiffsdieselmotoren aufzuzeigen, welche die zukünftigen Emissionsgrenzwerte einhält und zudem noch zu Kosteneinsparungen durch einen geringeren Brennstoffverbrauch beiträgt. Die Hauptkomponenten des Reformierungssystems umfassen im Wesentlichen einen autothermen Reformierungsreaktor sowie einen nachgeschalteten Entschwefelungsreaktor. Für den optimalen Betrieb der beiden Reaktoren wurde ein Verschaltungskonzept entwickelt und umgesetzt, welches durch zusätzliche Peripheriekomponenten wie Strömungsverteiler, Mischer und Wärmeübertrager ergänzt wurde. Diese haben die Aufgabe einen stabilen Reformierungs- und Entschwefelungsprozess zwischen 50 % bis 100 % Betriebslast zu gewährleisten, wofür diverse experimentelle und numerische Methoden zur Optimierung herangezogen wurden. Darüber hinaus wurde die Konzeptionierung der Gesamtverschaltung im Hinblick auf eine gute Regelbarkeit untersucht. Hierfür wurden mehrere Bypassschaltungen vorgesehen, welche bei Teillastbetrieb konstante Betriebstemperaturen am Eintritt des Entschwefelungsreaktors und der Brennstoffzellen ermöglichen. Für die Bestimmung der optimalen Betriebskenngrößen wurden umfangreiche Prozesssimulationen durchgeführt mit Hilfe deren die Auslegung der einzelnen Baugruppen erfolgte. Darüber hinaus wurden insbesondere die optimalen O/C- und S/C-Verhältnisse bestimmt, welche sowohl einen hohen Wirkungsgrad als auch die Einhaltung der Systemrandbedingungen gewährleisten. Mit Hilfe der ermittelten Betriebskenngrößen wurde ein Gesamtkonzept entwickelt, womit neben der konstruktiven Umsetzung insbesondere die Werkstoffauswahl für das druckbeaufschlagte System definiert werden konnte. Im Hinblick auf die Erzielung eines möglichst hohen Reformerwirkungsgrades unter stabilen Betriebsbedingungen wurde das Reformierungssystem als Kernkomponente eines Fuel Processing Moduls realisiert und charakterisiert. Hierbei konnte gezeigt werden, dass sich mit Hilfe des in dieser Arbeit entwickelten Systems ein stabiler Betrieb über mehrere Tage ohne Katalysatordeaktivierung realisieren lässt. Ebenfalls konnte ein modulierender Betrieb zwischen 50 % bis 100 % Betriebslast dargestellt werden, wobei alle Temperaturrestriktionen eingehalten wurden. Zusammenfassend kann festgehalten werden, dass mittels des entwickelten Reformierungssystems eine mögliche Alternative zu den bisherigen Schiffsdieselmotoren aufgezeigt wurde, welche in Kombination mit MCFC-Brennstoffzellen die zukünftig geforderten Schadstoffrestriktionen erfüllt.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Willem F.G. Van Rooijen; Committee Member: Ghiaasiaan, Seyed M; Committee Member: Weston M. Stacey

As the United States expands its quantity of nuclear reactors in the near future, the amount of spent nuclear fuel (SNF) will also increase. Closing the nuclear fuel cycle has become the next major technical challenge for the nuclear energy industry. By separating the transuranics (TRU) from the SNF discharged by Light Water Reactors, it is possible to fuel Advanced Burner Reactors to minimize the amount of SNF that must be stored in High Level Waste Repositories. One such ABR concept is the Subcritical Advanced Burner Reactor (SABR) being developed at the Georgia Institute of Technology. SABR is a subcritical, sodium-cooled fast reactor with a fusion neutron source capable of burning up to 25% of the TRU fuel over an 8.2 year residence time. In the SABR concept an annular core with a thickness of 0.6 m and an active height of 3.2 m surrounds the toroidal fusion neutron source. Neutron multiplication varies during the lifetime of the reactor from keff = 0.95 at the beginning of reactor life to 0.83 at the end of an equilibrium fuel cycle. Sixteen control rods worth 9$ are symmetrically positioned around the reactor. This thesis describes the dynamic safety analysis of the coupled neutron source, reactor core and reactor heat removal systems. A special purpose simulation model was written to predict steady-state conditions and accident scenarios in SABR by calculating the coupled evolution of the power output from the fusion and fission cores and the axial and radial temperature distributions of a fuel pin in the reactor. Reactivity Feedback was modeled for Doppler and sodium coolant voiding. SABR has a positive temperature reactivity feedback coefficient. A series of accident scenarios were simulated to determine how much time exists to implement corrective measures during an accident before damage to the reactor occurs.

Die vorliegende Arbeit beschäftigt sich mit der Entwicklung eines dieselbetriebenen autothermen Reformierungssystems (ATR-Einheit) zur Bereitstellung von wasserstoff- und kohlenmonoxidreichem Synthesegas für den maritimen Betrieb einer MCFC-Brennstoffzelle. Aufgrund der niedrigen Schadstoffemissionen sowie des hohen Wirkungsgrades hat dieses System das Potential eine mögliche Alternative zu den bisherigen Schiffsdieselmotoren aufzuzeigen, welche die zukünftigen Emissionsgrenzwerte einhält und zudem noch zu Kosteneinsparungen durch einen geringeren Brennstoffverbrauch beiträgt. Die Hauptkomponenten des Reformierungssystems umfassen im Wesentlichen einen autothermen Reformierungsreaktor sowie einen nachgeschalteten Entschwefelungsreaktor. Für den optimalen Betrieb der beiden Reaktoren wurde ein Verschaltungskonzept entwickelt und umgesetzt, welches durch zusätzliche Peripheriekomponenten wie Strömungsverteiler, Mischer und Wärmeübertrager ergänzt wurde. Diese haben die Aufgabe einen stabilen Reformierungs- und Entschwefelungsprozess zwischen 50 % bis 100 % Betriebslast zu gewährleisten, wofür diverse experimentelle und numerische Methoden zur Optimierung herangezogen wurden. Darüber hinaus wurde die Konzeptionierung der Gesamtverschaltung im Hinblick auf eine gute Regelbarkeit untersucht. Hierfür wurden mehrere Bypassschaltungen vorgesehen, welche bei Teillastbetrieb konstante Betriebstemperaturen am Eintritt des Entschwefelungsreaktors und der Brennstoffzellen ermöglichen. Für die Bestimmung der optimalen Betriebskenngrößen wurden umfangreiche Prozesssimulationen durchgeführt mit Hilfe deren die Auslegung der einzelnen Baugruppen erfolgte. Darüber hinaus wurden insbesondere die optimalen O/C- und S/C-Verhältnisse bestimmt, welche sowohl einen hohen Wirkungsgrad als auch die Einhaltung der Systemrandbedingungen gewährleisten. Mit Hilfe der ermittelten Betriebskenngrößen wurde ein Gesamtkonzept entwickelt, womit neben der konstruktiven Umsetzung insbesondere die Werkstoffauswahl für das druckbeaufschlagte System definiert werden konnte. Im Hinblick auf die Erzielung eines möglichst hohen Reformerwirkungsgrades unter stabilen Betriebsbedingungen wurde das Reformierungssystem als Kernkomponente eines Fuel Processing Moduls realisiert und charakterisiert. Hierbei konnte gezeigt werden, dass sich mit Hilfe des in dieser Arbeit entwickelten Systems ein stabiler Betrieb über mehrere Tage ohne Katalysatordeaktivierung realisieren lässt. Ebenfalls konnte ein modulierender Betrieb zwischen 50 % bis 100 % Betriebslast dargestellt werden, wobei alle Temperaturrestriktionen eingehalten wurden. Zusammenfassend kann festgehalten werden, dass mittels des entwickelten Reformierungssystems eine mögliche Alternative zu den bisherigen Schiffsdieselmotoren aufgezeigt wurde, welche in Kombination mit MCFC-Brennstoffzellen die zukünftig geforderten Schadstoffrestriktionen erfüllt.