The predicted shapes of voids and Xe bubbles in UO2

Abstract

Morphology is a fundamental attribute when investigating voids and bubbles in UO 2 . This study uses molecular dynamics and Monte Carlo simulations to predict the lowest energy shapes for voids and bubbles in UO 2 . The energies of the {100}, {110} and {111} surfaces have been calculated and used to predict the equilibrium void shape from Wulff construction. This equilibrium shape is compared to low energy faceted voids exhibiting different relative proportions of each family of terminating surfaces. It is found that the equilibrium Wulff shape does not represent the lowest energy morphology for nm void sizes at temperatures between 300 K and 1200 K. Furthermore, the lowest energy faceted voids are slightly more energetically favourable than spherical voids, and as Xe is added, and bubble pressure increases, the faceted morphology becomes even more favourable than the spherical shape.

Tomographic Study of Mesopore Formation in Ceria Nanorods

“…We distinguish (a) patches of high concentrations of any point defects (vacancies and interstitials), possibly combined with lattice swelling; 19 (b) agglomeration of these defects into clusters of ordered and neighboring point defects without forming voids; 11 , 20 and (c) micropores of sub-2 nm sized voids of irregular shape randomly distributed over all the volume. 10 , 13 , 21 , 22 (d) corresponds to internal mesopores of 2–10 nm size with well-faceted geometry, often termed “negative particles”, which are the topic of the present work; 13 , 23 , 24 , 28 (e) refers to surface pores (indents, recesses, and etch pits); 20 , 25 − 27 and (f) refers to through pores (nanochannels and wormhole shapes). 14 , 29 , 30 While cases (a, b) are commonly found as result of irradiation experiments, (c–f) more commonly stem from chemical processes, including etching, phase separation, reactions, and heat treatments.…”