Abstract
Within Europe 241 Am is a feasible alternative to 238 Pu that can provide a heat source for radioisotope thermoelectric generators (RTGs) and radioisotope heating units (RHUs) to be used in Electrical power sources used in outer planet missions. In the EPSO-SPACE* project developed as an exploratory research at JRC, a new type of nuclear power source, to provide heat and electricity for deep space missions is considered. It will consist of a 241 Am based compound with aerogel thermal insulation and thermocouples in close contact with the heat source. The assembly is inside an iridium encapsulation to withstand all relevant accident scenarios. The design will be modular and combinable for required electrical output.Several candidate Americium compounds will be investigated for chemical stability at high temperature and for self-irradiation damage. New thermo-electric converter materials containing actinides will be assessed, and a robust encapsulation designed. Safety analyses will be performed including launch explosion and re-entry accidents. The research will conclude in a conceptual design of a prototype power source. In the first part of this study, americium dioxide will be considered from the point of view of its chemical durability and of its behavior against radiation damage and helium formation, two aspects to be carefully investigated due to the high alpha-activity of the americium. Transmission electron Microscopy (TEM) and helium thermal desorption spectrometry (TDS) experiments will be described and results on aged (more than 30 years) AmO2 reported. Some comparison with 238 PuO2 based RTG’s will be discussed.
Highlights
In the space conquest century, several satellites are to be sent to the outer space
Within Europe 241Am is a feasible alternative to 238Pu that can provide a heat source for radioisotope thermoelectric generators (RTGs) and radioisotope heating units (RHUs) to be used in Electrical power sources used in outer planet missions
Several candidate Americium compounds will be investigated for chemical stability at high temperature and for self-irradiation damage
Summary
In the space conquest century, several satellites are to be sent to the outer space. In order to keep instruments running over several decades, with no direct physical contact to Earth, these space crafts need long-time batteries [1, 2]. 238Pu has been the isotope of choice for five decades. To be able to design suitable space batteries, more studies on 241AmO2 need to be made To this matter, a comparison between its microstructure evolution to the one of 238PuO2 can be of use. The point defects can precipitate into larger extended defects (e.g. dislocation loops) and the helium atoms into bubbles To observe these types of microstructural features the ideal probe is a Transmission Electron Microscope that enables with modern instrument to visualize objects in the nanometer (even lower) scale. An effect of self-radiation and radioactive decay is the change in impurity content of the compound, due to the ingrowing daughter(s). This change influences the electrical resistivity as well as the lattice parameters. Much more work was performed on 238PuO2 since this compounds has already been used in RTG's including batteries for space probes and even in pacemakers [8, 9]
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