Abstract
Thorium dioxide has recently regained interest as an alternative to uranium-based fuels due to its less
long-lived transuranium element production or its higher natural abundance, among others. Though,
ThO2 pellet production faces many challenges such as reaching high theoretical densities. This can be
improved by sintering the pellets, but this treatment is altered by many factors. In fact, a release of
adsorbed gases was observed which can negatively change the grain growth. This thesis presents a
systematic study on the adsorption of CO2 and H 2O on two types of ThO2 powders reproducing storage
conditions, one derived from thorium oxalate (ThO_OX) and one from a novel 2-step alkali
precipitation route (ThO_TSA). Both materials were characterized by means of N 2 adsorption isotherm
at 77K, SEM and TEM. Moreover, CO2 and H 2O desorption was experimentally studied by TGA coupled
to mass spectrometry. Surface analysis indicates that both materials are non-rigid aggregates with
mesoporosity attributed to interparticular cavities which agrees with the SEM and TEM images.
However, SEM/TEM also shows that the particle shapes differ significantly, being plate-like for
ThO_Ox, and sphere-like for ThO_TSA. The powders retained CO2 adsorbed well above 600°C, and it
seems the adsorbed water has a significant effect on the CO2 adsorption. ThO_TSA reached the
saturation point earlier than ThO_Ox, suggesting a lower gas adsorption capacity. Therefore, the 2-
step alkali precipitation route is recommended for long ThO2 powder storage periods.
Details
Original language | English |
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Qualification | Master of Science |
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Awarding Institution | - Uhasselt - Hasselt University
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Supervisors/Advisors | |
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Award date | 8 Jun 2020 |
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Publisher | - UHasselt - Universiteit Hasselt
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Publication status | Published - 19 Jun 2020 |
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