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Behaviour of rare confined gases in a high-temperature ceramic matrix: modelling through semi-empirical approaches

Jack Arayro has defended his thesis on 18th December 2015 at CINAM of Marseille (France).​

Document type > *Mémoire/HDR/Thesis

Keywords >

Research Unit > IRSN/PSN-RES/SEMIA/LPTM

Authors > ARAYRO Jack

Publication Date > 18/12/2015

Summary

Uranium dioxide UO2 is the standard fuel in nuclear pressurized water reactors (PWR).
During the operation of the reactor the fuel pellets undergo thermal and mechanical stresses.
For this reason it is very important to understand these thermomechanical properties of this
system both in normal operation conditions and accidental situations (300 to 2000K). During
fission reactions of uranium, rare gases such as xenon are produced within the fuel. Due
to their low solubility, these gases will either be released or form intra- and inter-granular
bubbles inside the UO2. The presence of these bubbles in the fuel has an impact on the
thermomechanical properties of the latter. We focus in this thesis on the study of intragranular
bubbles and their impact on the thermomechanical properties of UO2, through modeling at the
atomic scale. At this scale, intragranular bubbles take the shape of an octahedron, presenting
mainly (111) and (100) facets. Given the complexity of the study of the stability of this
octahedron, we have simplified the problem in order to study it in a more systematic way
and to decouple the various effects. First, the stability of (100) and (111) extended surfaces of
UO2 and microscructural modifications generated by their relaxation were studied. In a second
step, we dermined adsorption isotherms of xenon on these relaxed surfaces, and compared them to the incorporation ones inside an empty box in order to isolate surface effects. A specific attention has been given to the microstructure of xenon in these systems. Finally, an analysis of the mechanical properties (pressure and stress profiles near by the surface) was achieved in order to get the pertinent quantities that will fed-up micromechanical models at higher scale.

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