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This thesis explores the process development and scale-up challenges for the immobilisation of plutonium containing wastes and residues. The first section details the difficulties encountered with utilising an attrition mill operated in the dry mode to prepare zirconolite samples for consolidation by hot isostatic processing. The failure to remove the milling additives from the milled powders led to porous and heterogeneous products with no correlation between the candidate wasteform properties and milling conditions. Similar attrition milling conditions were examined with a zirconia candidate wasteform. Pellets, prepared by cold isostatic and cold uniaxial pressing, showed a clear correlation between the increased milling aggressiveness and the density and microstructure of the products. Cold isostatic pressing produced pellets with the highest density. The effect of precursor particle size, by utilising manufacturer size defined precursors, showed that homogenous and dense zirconolite products could be manufactured by HIP. The experiment confirmed that the failure to remove the lubricant from the HIP cans led to low quality products. Further work examined the effect that different precursor treatments had on the ability of zirconolite precursors to be planetary milled. The powders were pressed into pellets and sintered in either air or nitrogen. The air sintered pellets were all highly porous but homogenous whilst the nitrogen sintered pellets were heterogeneous. The difference in sintering behaviour was determined to be the result of a eutectic point between the iron and titanium oxides. Brief studies examined how the density and homogeneity of zirconolite samples improve with increased milling durations. Another experiment attempted to demonstrate a fine precursor digestion method that did not work. Modified attrition mill internals are also considered. Finally, the impact of this work on the design of a candidate bulk plutonium immobilisation plant is discussed as well as the on going experimentation with uranium active samples.

This thesis presents a novel path planning algorithm for robotic crowd navigation through a pedestrian environment. The robot is designed to negotiate its way through the crowd using considerate movements. Unlike many other path planning algorithms, which assume cooperation with other pedestrians, this algorithm is completely independent and requires only observation. A considerate navigation strategy has been developed in this thesis, which utilises consideration as an directs an autonomous mobile robot. Using simple methods of predicting pedestrian movements, as well as simple relative distance and trajectory measurements between the robot and pedestrians, the robot can navigate through a crowd without causing disruption to pedestrian trajectories. Dynamic pedestrian positions are predicted using uncertainty ellipses. A novel Voronoi diagram-visibility graph hybrid roadmap is implemented so that the path planner can exploit any available gaps in between pedestrians, and plan considerate paths. The aim of the considerate path planner is to have the robot behave in specific ways when moving through the crowd. By predicting pedestrian trajectories, the robot can avoid interfering with them. Following preferences to move behind pedestrians, when cutting across their trajectories; to move in the same direction of the crowd when possible; and to slow down in crowded areas, will prevent any interference to individual pedestrians, as well as preventing an increase in congestion to the crowd as a whole. The effectiveness of the considerate navigation strategy is evaluated using simulated pedestrians, multiple mobile robots loaded with the path planning algorithm, as well as a real-life pedestrian dataset. The algorithm will highlight its ability to move with the aforementioned consideration towards each individual dynamic agent.

A combination of electron microscopy analysis and micromagnetic modelling was used to study the microstructure role on the performance of commercial sintered Nd-Fe-B magnets that are used in wind power units. These magnets were observed to be composed of Nd2Fe14B phase grains with different Dy content, size distribution and anisotropy orientation. The grains were surrounded by intergranular phases with different Fe/rare-earth ratios. The magnetic characterisation of these samples revealed that it is possible for Dy-free samples to have higher coercivities than Dy-containing samples with the control of the microstructure. Micromagnetic modelling revealed that decreasing the angular dispersion of Nd2Fe14B grain anisotropy provides the most significant increase to coercivity. For example, decreasing this angular dispersion from 30° to 1° increased the coercivity by 25% of its initial values. In addition, the presence of intergranular phases with high Fe/rare-earth ratios (Fe-like) led to the generation of reversed domain walls at low applied field. The formation of non- ferromagnetic intergranular phases (low Fe/rare-earth) led to 8% increase in coercivity; however, it led to step-wise hysteresis loops. On the other hand, the effect of grain size distribution on coercivity was found to be less significant compared to previous features. Micromagnetic modelling of grain boundary diffused samples revealed that the coercivity may increase with increasing the thickness and Dy concentration of Dy-rich shells. In addition, the higher rare-earth content at the intergranular regions of these samples was revealed to be beneficial to coercivity. Finally, the possibility of twinning in main phase grains showed a detrimental effect on the coercivity. The formation of non-ferromagnetic intergranular phases may reduce the effect of twinned grains and increase coercivity but no significant increase in remanence and maximum energy density was observed. These insights could be useful to produce sintered Nd-Fe-B magnets with higher coercivity and lower heavy rare-earth content.