Sintering trials of analogues of americium oxides for radioisotope power systems

E.J Watkinson,R.M Ambrosi,D.P Kramer,H.R Williams,M.J Reece,K Chen,M.J Sarsfield,C.D Barklay,H Fenwick,D.P Weston,K Stephenson

doi:10.1016/j.jnucmat.2017.04.028

Abstract

European Space Agency radioisotope power systems will use americium oxide as the heat source in pellet or disc form. The oxide form is yet to be decided. Sintering trials with CeO2 and Nd2O3 as analogues for AmO2 and Am2O3 were conducted. Spark plasma sintering (SPS) and cold-press-and-sinter methods were compared. Different sintering parameters and particle characteristics were investigated with commercial and synthesised powders. The synthesised powders contained lath-shaped particles, and batches with different particle sizes and specific surface areas were made and sintered. This is the first study in the public literature to report the sintering of lath-shaped CeO2.The targeted density range of 85–90% was met using both techniques. No ball-milling was required. Cold-pressing-and-sintering CeO2 produced intact discs. Large cracking was prevalent in the SPS discs. Some powders pressed more successfully than others. Powder morphology had a significant effect on the result but it was not possible to fully quantify the effects in this study. The cold-pressed-and-sintered CeO2 discs had comparable Vickers hardness values to a nuclear ceramic (UO2). The hardness values were greater than the spark plasma sintered CeO2 sample. Efforts to SPS near-net shaped pellets using CeO2 and Nd2O3 are reported. A follow on investigation was conducted to assess how the 85–90% T.D. target could be achieved. The aspect ratio impacts the sintering parameters and behaviour. The Vickers hardness of Nd2O3 is reported for the first time and compared to the results of sintered CeO2.

Highlights

Radioisotope power systems (RPS) enable deep space exploration as well as the ability to probe some of the more challenging environments on the surfaces of solar system bodies
The versatility of radioisotope thermoelectric generators (RTGs) and radioisotope heater units (RHUs) has enabled a range of space missions since the 1960s that would not have been possible with solar power [1,2,3]
The European Space Agency (ESA) programme has since progressed to the production and processing of americium oxide, and the development of different RPS technologies including RTGs [5], RHUs and Stirling generators [4]

Summary

Introduction

Radioisotope power systems (RPS) enable deep space exploration as well as the ability to probe some of the more challenging environments on the surfaces of solar system bodies. The versatility of radioisotope thermoelectric generators (RTGs) and radioisotope heater units (RHUs) has enabled a range of space missions since the 1960s that would not have been possible with solar power [1,2,3]. Americium-241 (241Am) was identified as a viable and affordable fuel for Europe [4] It was selected as the radioisotope fuel despite its reduced specific thermal power compared to 238Pu [8]. The ESA programme has since progressed to the production and processing of americium oxide, and the development of different RPS technologies including RTGs [5], RHUs and Stirling generators [4]

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