Microstructural evolution of uranium dioxide following compression creep tests: An EBSD and image analysis study

Abstract

International audienceSintered UO2 pellets with relatively large grains (similar to 25 pm) are tested at 1500 degrees C under a compressive stress of 50 MPa, at different deformation levels up to 12%. Electron Back Scattered Diffraction (EBSD) is used to follow the evolution, with deformation, of grains (size, shape, orientation) and sub-grains. Image analyses of SEM images are performed to characterize emergence of a population of micron size voids. For the considered microstructure and test conditions, the results show that the deformation process of UO2 globally corresponds to grain boundary sliding, partly accommodated by a dislocational creep within the grains, leading to a highly sub-structured state

Influence of strain conditions on the grain sub-structuration in crept uranium dioxide pellets

“…2b). Damages in the form of inter-granular cavities, have been observed in certain previous studies performed on UO 2 pellets with grain sizes varying from 9 to 36 mm [8,12]. In this study, such damages were only observed at the highest strain rate and level (sample D9), in the central part of the pellet, as illustrated in Fig.…”

“…Fig. 2b), whereas numerous ones were observed by other authors in pellets deformed under conditions similar to those used in the present work [8,12]. This difference could be related in part to the size of our pellets.…”

“…These cavities are globally elongated in a direction parallel to the compression axis, in accordance with results given in Refs. [8,12].…”

A new characterization approach for studying relationships between microstructure and creep damage mechanisms of uranium dioxide

“…Densities were measured by an immersion method. Grain sizes were measured by EBSD on surfaces of about 0.5 mm 2 , considering a 5 critical disorientation angle for grain boundaries detection [14].…”

“…These pellets were submitted to compression creep tests at relatively high stress levels at 1500 C, performed up to mean deformations of the order of 8%. Their microstructures were characterized before and after mechanical test, mainly by scanning electron microscopy (SEM), coupled with image analysis, and electron backscattered diffraction (EBSD), on the basis of a methodology that has been previously implemented on other UO 2 samples [14]. The potential of this approach to determine quantified microstructural characteristics, before and especially after creep tests, is more particularly evaluated.…”