No description available.

No description available.

Grade 91 (Gr.91) is a common structural material used in boiler applications and is favored due to its high temperature creep strength and oxidation resistance. Under cyclic stresses, the material will experience creep deformation eventually causing the propagation of type IV cracks within its heat-affected-zone (HAZ) which can be a major problem under short-term and long-term applications. In this study, we aim to improve this premature failure by performing a computational thermodynamic study through the Calculation of Phase Diagram (CALPHAD) approach. Under this approach, we have provided a baseline study as well as simulations based on additional alloying elements such as manganese (Mn), nickel (Ni), and titanium (Ti). Our simulation results have concluded that high concentrations of Mn and Ni had destabilized M23C6 for short-term creep failure, while Ti had increased the beneficial MX phase, and low concentrations of nitrogen (N) had successfully destabilized Z-phase formation for long-term creep failure.

No description available.

Eksamineringspraktyke in skole in Namibie is die fokuspunt van hierdie studie. 'n Historiese ondersoek is ingestel na die bree, algemene eksamenstelsels van die verlede. Op grond van die tekortkominge en gebreke van die Kaaplandse Onderwysdepartement-eksamenstelsel, is die noodsaaklikheid en wenslikheid van die herbeplanning en verbetering van die eksamenstelsel uitgelig. Daar is gefokus op die HIGHERIINl'ERNATIONAL GENERAL CERTIFICATE OF SECONDARY EDUCATION-eksamenstelsel, ten einde vas te stel of algemene erkende opvoedkundige beginsels, prosedures en werkswyses tot op datum in die eksamenstelsel vergestalt is. 'n Uitvloeisel van die bevindings in hierdie studie is dat die huidige eksamenstelsel tekortkominge weerspieel, maar dat die historiese beperkinge oorbrug kan word Die afleiding word gemaak dat alle onderwysbelanghebbendes moet saamwerk aan verbeteringstrategiee ten opsigte van die huidige eksamenstelsel. Die hoop word uitgespreek dat die hele eksamenstelsel so spoedig moontlik, maar na deeglike beplanning, volledig sal verinheems. / Examination practices in schools in Namibia is the focal point of this study. An historical research has been done into the general examination systems of the past On account of the shortcomings and constraints of the Cape Education Deparbnent examination system, the necessity and desirability of the restructuring and betterment of the examination system is highlighted. The emphasis is put on the HIGHER/ INI'ERNATIONAL GENERAL CERTIFICATE OF SECONDARY EDUCATION to determine whether generally accepted educational principles, procedures and methods have been embodied in the examination system. The present Namibian examination system is still insufficient. However, much can be done to overcome the historical constraints. The conclusion was reached that each and every stakeholder should work together to devise strategies for the betterment of the examination system. The author trusts that the whole examination system will, as soon as possible but after thorough planning, become totally indigenous. / Educational Studies / M. Ed. (Historiese Opvoedkunde)

Eksamineringspraktyke in skole in Namibie is die fokuspunt van hierdie studie. 'n Historiese ondersoek is ingestel na die bree, algemene eksamenstelsels van die verlede. Op grond van die tekortkominge en gebreke van die Kaaplandse Onderwysdepartement-eksamenstelsel, is die noodsaaklikheid en wenslikheid van die herbeplanning en verbetering van die eksamenstelsel uitgelig. Daar is gefokus op die HIGHERIINl'ERNATIONAL GENERAL CERTIFICATE OF SECONDARY EDUCATION-eksamenstelsel, ten einde vas te stel of algemene erkende opvoedkundige beginsels, prosedures en werkswyses tot op datum in die eksamenstelsel vergestalt is. 'n Uitvloeisel van die bevindings in hierdie studie is dat die huidige eksamenstelsel tekortkominge weerspieel, maar dat die historiese beperkinge oorbrug kan word Die afleiding word gemaak dat alle onderwysbelanghebbendes moet saamwerk aan verbeteringstrategiee ten opsigte van die huidige eksamenstelsel. Die hoop word uitgespreek dat die hele eksamenstelsel so spoedig moontlik, maar na deeglike beplanning, volledig sal verinheems. / Examination practices in schools in Namibia is the focal point of this study. An historical research has been done into the general examination systems of the past On account of the shortcomings and constraints of the Cape Education Deparbnent examination system, the necessity and desirability of the restructuring and betterment of the examination system is highlighted. The emphasis is put on the HIGHER/ INI'ERNATIONAL GENERAL CERTIFICATE OF SECONDARY EDUCATION to determine whether generally accepted educational principles, procedures and methods have been embodied in the examination system. The present Namibian examination system is still insufficient. However, much can be done to overcome the historical constraints. The conclusion was reached that each and every stakeholder should work together to devise strategies for the betterment of the examination system. The author trusts that the whole examination system will, as soon as possible but after thorough planning, become totally indigenous. / Educational Studies / M. Ed. (Historiese Opvoedkunde)

The aim of this work was to study the separate effect of fission fragment damage on the structural integrity and matrix dissolution of uranium dioxide in water. Radiation damage similar to fission damage was created by irradiating bulk undoped and doped ‘SIMFUEL’ disks of UO2, undoped bulk CeO2 and thin films of UO2 and CeO2 with high energy Xe and U ions. The UO2 thin films, with thicknesses in the range of 90 – 150 nm, were deposited onto (001), (110) and (111) orientations of single crystal LSAT (Al10La3O51Sr14Ta7) and YSZ (Yttria-Stabilised Zirconia) substrates. The CeO2 thin films were deposited onto single crystal silicon (001) substrates. Part of the bulk UO2 and CeO2 samples, the thin films of UO2 on the LSAT substrates and the thin films of CeO2 were irradiated with 92 MeV 129Xe23+ ions to a fluence of 4.8 × 1015 ions/cm2 to simulate the damage produced by fission fragments in uranium dioxide nuclear fuel. Part of the bulk UO2 and CeO2 samples and the thin films of UO2 on the YSZ substrates were irradiated with 110 MeV 238U31+ ions to a fluence of 5 × 1010, 5 × 1011 and 5 × 1012 ions/cm2 to study the accumulation of the damage induced. The irradiated and unirradiated samples were studied using scanning electron microscopy (SEM), focused ion beam (FIB), atomic force microscopy (AFM), energy dispersive X-ray (EDX) spectroscopy, electron probe microanalysis (EPMA), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS) techniques to characterise the as-produced samples and assess the effects of the ion irradiations. Dissolution experiments were conducted to assess the effect of the Xe ion irradiation on the dissolution of the thin film UO2 samples on the LSAT substrates and the bulk and thin film CeO2 samples. The solutions obtained from the leaching of the irradiated and unirradiated samples were analysed using inductively coupled plasma mass spectrometry (ICP-MS). XRD studies of the bulk UO2 samples showed that the ion irradiations resulted in an increased lattice parameter, microstrain and decreased crystallite size, as expected. The irradiated UO2 thin films on the LSAT substrates underwent significant microstructural and crystallographic rearrangements. It was shown that by irradiating thin films of UO2 with high energy, high fluence ions, it is possible to produce a structure that is similar to a thin slice through the high burn-up structure. It is expected that the ion irradiation induced chemical mixing of the UO2 films with the substrate elements (La, Sr, Al, Ta). As a result, a material similar to a doped SIMFUEL with induced radiation damage was produced.