Space Nuclear Power Systems: Enabling Innovative Space Science and Exploration Missions
thesisposted on 01.11.2017, 09:53 by Emily Jane Watkinson
The European Space Agency’s (ESA’s) 241Am radioisotope power systems (RPSs) research and development programme is ongoing. The chemical form of the americium oxide ‘fuel’ has yet to be decided. The fuel powder will need to be sintered. The size and shape of the oxide powder particles are expected to influence sintering. The current chemical flow-sheet creates lath-shaped AmO2. Investigations with surrogates help to minimise the work with radioactive americium. This study has proposed that certain cubic Ce1-xNdxO2-(x/2) oxides (Ia-3 crystal structures with 0.5 < x < 0.7) could be potential surrogates for some cubic AmO2-(x/2) phases. A new wet-chemical-synthesis-based process for fabricating Ce1-xNdxO2-(x/2) with a targeted x-values has been demonstrated. It uses a continuous oxalate coprecipitation and calcination route. An x of 0.6 was nominally targeted. Powder X-ray diffraction (PXRD) and Raman spectroscopy confirmed its Ia-3 structure. An increase in precipitation temperature (25 °C to 60 °C) caused an increase in oxalate particle median size. Lath/plate-shaped particles were precipitated. Ce Nd oxide PXRD data was Rietveld refined to precisely determine its lattice parameter. The data will be essential for future sintering trials with the oxide where variations in its crystal structure during sintering will be investigated. Sintering investigations with micrometric CeO2 and Nd2O3 have been conducted to understand how AmO2 and Am2O3 may sinter. This is the first reported pure Nd2O3 spark plasma sintering (SPS) investigation. A comparative study on the SPS and the cold-press-and-sinter of CeO2 has been conducted. This is the first study to report sintering lath-shaped CeO2 particles. Differences in their sizes and specific surface areas affected powder cold-pressing and caused variations in cold-pressed-and-sintered CeO2 relative density and Vickers hardness. The targeted density range (85-90%) was met using both sintering techniques. The cold-press-and-sinter method created intact CeO2 discs with reproducible geometry and superior Vickers hardness to those made by SPS.