Mastication is a fuel management technique that disrupts the vertical continuity of forest fuels by mechanical shredding of trees and understory vegetation into a highly-compacted surface fuelbed. The particle size distributions, bulk density and arrangements differ from natural and slash fuel types, thus resulting in fuelbeds with potentially different moisture dynamics and fire behaviour. We conducted three experiments, the first of which examined differences in in-stand micrometeorology and fuelbed moisture content between differing levels of stand thinning via mastication. In the second experiment, a fuel moisture model was created, validated with an independent dataset, and compared with pre-existing models that are incorporated in the Canadian Forest Fire Danger Rating System. In the third experiment, we compared the results of standard ignition tests performed on masticated fuelbeds in the laboratory and field to determine probability of sustained flaming, and compared our findings with pre-existing models of ignition for other forest fuels.

D.Phil. / The existence of radioactive waste (or ‘radwaste’) has become a problem that afflicts the nuclear industry worldwide. The search for a social consensus on radwaste management strategies is proving to be one of the most complex challenges facing nuclear technological development. The categories of radwastes that are currently of greatest concern are spent nuclear fuel (SF) that is discharged from nuclear power reactors and high level waste (HLW) arising from reprocessing of SF, as they continue to accumulate in storage facilities around the world and perceived to be without an end solution to their existence. Like many other nuclear countries, South Africa too is facing major decisions about future management of SF that is generated from its nuclear power and research reactors. It remains undecided on which of the available spent fuel management (SFM) options it must adopt. This research study seeks to produce a framework for evaluating SFM options that will identify and characterise the elements or aspects to be analysed, and use it to evaluate the SFM options in order to identify a preferred or optimum option for South Africa. The methodological approach to this study involves the use of literature research, a case study on Eskom’s SFM approach and a questionnairebased survey complemented by in-depth interviews with key stakeholders of nuclear power in South Africa. These qualitative methods are used to verify and validate the SFM evaluation framework. To complement the qualitative approach, a cost analysis of the options based on input from Eskom and literature data as well as on assumed scenarios, is carried out. Both the qualitative and the cost analysis lead to identification of a preferred SFM option for South Africa. Three principal SFM options were identified and evaluated: the reprocessing and recycling (or closed fuel cycle) option, the direct disposal (or once-through fuel cycle) option, and the indefinite storage (or deferral-of-a-decision) option. There are at least nine categories of issues that have been identified as factors affecting these SFM options: technology, safety, environmental impact, proliferation resistance, physical security, economics, sociopolitical influence, ethical principles and institutional capability. These formed the evaluation framework and were used as the criteria for the assessment of the SFM options. Based on the analysis conducted in the study concerning the feasibility of the SFM options for the South African context in terms of these criteria, it is concluded that the direct disposal option is the most favourable option for implementation in the South African nuclear power programme. However, all three options have their technical merits but are also contentious in various degrees both within the nuclear industry and the public domain.

Fuels management in eucalyptus plantations is essential to minimise the impact of wildfire. Prescribed burning has the potential to reduce the fuel hazard in plantations, but is not routinely conducted due to concerns relating to tree damage. Through a series of experimental burns, the issues of tree damage are addressed and minimum tree sizes are recommended that are capable of withstanding the effects of low to moderate intensity fires. Data was collected between 2005 and 2007 over six sites, two species, and three age classes. Tree response results came from multiple measurements of over 1700 individual trees. The fuel characteristics commonly found in sub-tropical eucalypt plantations from age four to eleven are described and quantified. These fuel characteristics are related to fire behaviour and new fire behaviour models, specific to young eucalypt plantations, are presented. The fuel characteristics that most influence fire behaviour in young eucalypt plantations are fuel load, fuel height, and fuel moisture content. These characteristics can be used to predict the rate of spread of a plantation fire under benign wind conditions. A novel technique for assessing the extent of stem damage in eucalypts is developed and described. This technique enables immediate assessment of stem damage following fire; previous assessment techniques recommend waiting a considerable period of time (up to 2 years) until dead bark dropped off and fire scars were evident. This new assessment technique is likely to be suitable for post-fire assessment of any eucalypt species and will provide forest managers with the capability of deciding whether to leave a stand to ???grow-on??? or commence recovery operations. Minimum stem sizes recommended to ensure no long-term damage are between 5 ??? 8 cm DBH (diameter at breast height, i.e. 1.3m above ground level) for Eucalyptus dunnii (Dunn???s white gum) and 5 ??? 13 cm DBH for Corymbia spp. (spotted gum) depending on the quantity of fuel around the stem. Stem sizes vary between species because of the variation in bark thickness between species. This thesis provides all the necessary information to conduct prescribed burning operations in young eucalypt plantations.