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

Abstract

h i g h l i g h t s Four different UO 2 pellets batches are microstructurally compared, before and after compression creep tests. Development of sub-boundaries within the original grains, in crept samples, is quantified by EBSD. Links are observed between the intra-granular pores population of the as-sintered samples, their creep rate and their sub-structured state, after mechanical tests.

Sub-boundaries induced by dislocational creep in uranium dioxide analyzed by advanced diffraction and channeling electron microscopy

“…It opens the way to apply Accurate-ECCI on submicron sized grains [27]. Dislocations in creep deformed UO 2 can now be observed by A-ECCI as demonstrated in [28] while in the past they were only analyzed by TEM [3,4]. Furthermore, continuous progress in EBSD detectors and diffraction patterns analysis offer now improved angular resolution to reliably quantify the low angle boundaries and the subsequent network of geometrically necessary dislocations (GND) [29][30][31][32][33].…”

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

“…Small round fabrication voids are observed in intra-and inter-granular locations. The surface fraction of these voids was evaluated at 1.7% by image analysis using the AnalySIS image software [13,14]. This value is slightly different from that expected from density measurements (i.e.…”

“…Complementary details concerning the testing machine characteristics can be found in Refs. [8,13,20]. The cooling rate, after all tests, was 17 C per min.…”

Effects of U-Mo Irradiation Creep Performance on the Thermo-Mechanical Coupling Behavior in U-Mo/Al Monolithic Fuel Assemblies

“…Complicated in-pile thermo-mechanical behavior appears in U-Mo/Al monolithic fuel assemblies (Miller et al, 2010;Kim et al, 2012;Deng et al, 2017), which mainly depends on the following contributions: 1) the deformations (Miller et al, 2010;Kim and Hofman, 2011;Kim et al, 2013;Meyer et al, 2014;Zhao et al, 2015) induced by irradiation swelling and creep of fuel foil (Kim et al, 2013;Kim and Hofman, 2011); 2) the plasticity and thermal creep performances of cladding (Yan et al, 2017;Jian et al, 2019a); 3) formation of porous fuel structure due to the fission-gas-resulted bubbles (Rest, 2010;Meyer et al, 2014); 4) the acceleration of fission gas swelling driven by grain recrystallization (Rest, 2010); 5) the degradations of thermo-mechanical properties and macroscale strength owing to the formed porous structure, pore pressure and the possible creep damage in the fuel foil (Rest, 2010;Robinson et al, 2008;Iltis et al, 2016;Yan et al, 2017;Salvato et al, 2018;Jian et al, 2019a;Schulthess et al, 2019); 6) the complex mechanical interactions across all the parts, including the fuel plates, the outside Al plates and the side plates (Deng et al, 2017). On one hand, the irradiation creep strains will relax the stresses in the fuel foils or the other parts.…”

“…On one hand, the irradiation creep strains will relax the stresses in the fuel foils or the other parts. On the other hand, the high creep strains will result in creep damage and degradation of fuel strength (Iltis et al, 2016;Jian et al, 2019a). It is necessary to examine the effects of fuel creep performance on the thermal-mechanical behavior in U-Mo/Al fuel assemblies, which will supply a basis for advanced fuel design.…”