Defect energetics and Xe diffusion in UO2 and ThO2

First-principles design of next-generation nuclear fuels

“…The migration energies of single vacancies in ThO 2 (see Table II ) are predicted to be signifi cantly higher than those in UO 2 . 15 The assisting infl uence of a V O was not observed in the movement of a Th vacancy. DFT studies thus predict that point defects are less easily created as well as less mobile in ThO 2 than in UO 2 .…”

“…Therefore, based on the defect energetics, it is expected that fi ssion gas atoms are less mobile in ThO 2 than in UO 2 . Further calculations were conducted to understand diffusion behavior of fi ssion gas atoms in ThO 2 and UO 2 , and it was reported 15 that Xe, which is one of the highest fractional released fi ssion gases in UO 2 , is more likely to diffuse in UO 2 than in ThO 2 . Figure 3a and 3b show the electron charge distribution of UO 2 and ThO 2 , respectively, and clearly illustrate the different behavior of Xe in the two oxides.…”

“…Various actinide compounds, including UC and U-Pu-C alloys, have also recently been investigated as candidate fuels for next-generation reactors. 20,21 The intricate nature of the 5 f electrons in the actinides is crucial to understanding nuclear fuel properties such as chemical bonding, heat conductivity, 22 fi ssion gas behavior, 11,12,[14][15][16][17][18][19] and the surface interaction with molecules 23 relevant to fuel corrosion. 24 Hence, understanding actinide electronic structure is a prerequisite for understanding the behavior of nuclear fuel materials.…”

“…In fact, fi rstprinciples studies based on density functional theory (DFT) have already greatly contributed by supplying fundamental electronic-structure knowledge [1][2][3][4][5][6][7][8] and the material properties of defect-containing nuclear fuels. [9][10][11][12][13][14][15][16][17][18][19][20] Among all fuel materials, UO 2 and PuO 2 have been most extensively studied both experimentally and computationally. This is especially true for UO 2 , the standard nuclear fuel for light water reactors.…”

Energetics of halogen impurities in thorium dioxide

“…Conversely, thoria has been less well studied. Some atomic scale modelling studies on trapping and diffusion of the volatile fission products (Xe, Br, Rb and Cs) [18,20] have been reported but these only considered the incorporation of impurity atoms in neutral point defects and neutral clusters of defects, leaving aside the possibility of incorporation in charged defect configurations. A more extensive study of Xe and Kr has been made [21], which did consider charged as well as neutral defect sites.…”