Study of Ba and Zr stability inUO2±xby density functional calculations

Abstract

Barium and zirconium behavior in nuclear fuels is investigated using density functional theory ͑DFT͒. More particularly, incorporation and solution energies of Ba and Zr in preexisting trap sites of UO 2 ͑vacancies, interstitials, U-O divacancy, and Schottky trio defects͒ are calculated using the projector-augmented-wave method as implemented in the Vienna ab initio simulation package ͑VASP͒. Correlation effects are taken into account within the DFT+ U approach. Our results are discussed in relation to those based on conventional functionals and with available experimental data. For both functionals, zirconium is found to be much more soluble than barium. However, the most favorable solution site depends on the treatment of correlation effects, the difference between DFT+ U and DFT based results being more pronounced for Zr than for Ba. We also demonstrate that the solution process for more complex phases like BaO, ZrO 2 , BaUO 3 , and BaZrO 3 are very sensitive to the correct description of correlation effects in UO 2 .

Progress in understanding fission-product behaviour in coated uranium-dioxide fuel particles

“…between 1973 and 2173 K), some experimental observations seem to evidence the same thermodynamic behaviour [36] Ab initio calculations [42] have recently shown that incorporation of caesium in slightly hyperstoichiometric UO 2+x could be favoured in case of increase of uranium vacancy concentration which happens in fuel submitted to irradiation (exactly as for zirconium, as previously discussed). Nevertheless, incorporation (or solution) energy of caesium in uranium vacancy [42] is considerably lower than for zirconium [37]. For that reason, its behaviour is expected to be different from that of zirconium.…”

U and Xe transport in UO2±x: Density functional theory calculations

“…In order to simplify the calculation of defect properties the latter two contributions are ignored in the present study. Recent reports have shown that the LDA/GGA+U methodology correctly describes many of the relevant properties of UO 2 and UO 2+x 42,[44][45][46][47][48][49][50][51][52][53][54][55][56] . In accordance with earlier LDA+U studies the U and J values were set to U = 4.5 eV and J = 0.51 eV 46 .…”

Fission products stability in uranium dioxide

“…In order to better describe the localization of the f electrons of uranium in this compound, the GGA+U functional can be considered [12,13]. Very recently, we showed that the use of GGA+U functional leads to a better agreement with experimental data for solution energies of fission products, namely Ba, Zr, Cs and Mo in urania [14][15][16]. In this contribution, we extend our calculations of solution energies with GGA+U functional to He and other important FP for safety like Kr, Xe, I, Te, Ru, Sr and Ce.…”